{"success":true,"version":"v1","request":{"tool":"list_calculators","category":"engineering"},"result":{"entity_type":"calculator_list","status":"completed","count":25,"calculators":[{"calculator_id":"led-resistor","entity_type":"calculator","name":"LED Resistor Calculator","category":"engineering","tool_name":"calculate_led_series_resistor","description":"Computes the current-limiting series resistor for one or more LEDs in series from the supply voltage, LED forward voltage and desired current, then picks the nearest E12 and E24 preferred values, a safe (rounded-up) E24 value and the resistor power rating.","use_when":"You are wiring an LED (or a string of LEDs in series) to a DC supply and need the resistor value, a standard part value and its wattage.","do_not_use_when":"LEDs are in parallel (each branch needs its own resistor), you drive high-power LEDs with a constant-current driver, or you only need Ohm's law (use ohms-law).","required_inputs":["supply_voltage_v"],"optional_inputs":["led_forward_voltage_v","led_current_ma","leds_in_series"],"urls":{"html":"https://tttkmbb.com/engineering/led-resistor","markdown":"https://tttkmbb.com/engineering/led-resistor.md","schema":"https://tttkmbb.com/api/v1/calculators/led-resistor","api":"https://tttkmbb.com/api/v1/calculate/led-resistor"}},{"calculator_id":"voltage-divider","entity_type":"calculator","name":"Voltage Divider Calculator","category":"engineering","tool_name":"calculate_voltage_divider","description":"Computes the output voltage of a two-resistor divider (Vout = Vin·R2/(R1+R2)), the current through the chain and the power in each resistor, or solves for R2 when a target output voltage is given.","use_when":"You need the voltage at the junction of two series resistors, the R2 that produces a target voltage, or the power each resistor must handle.","do_not_use_when":"The output is loaded by a low-impedance load (the load parallels R2 and lowers Vout), you need a regulated supply, or you are limiting LED current (use led-resistor).","required_inputs":["input_voltage_v","r1_ohm"],"optional_inputs":["r2_ohm","target_output_voltage_v"],"urls":{"html":"https://tttkmbb.com/engineering/voltage-divider","markdown":"https://tttkmbb.com/engineering/voltage-divider.md","schema":"https://tttkmbb.com/api/v1/calculators/voltage-divider","api":"https://tttkmbb.com/api/v1/calculate/voltage-divider"}},{"calculator_id":"resistor-color-code","entity_type":"calculator","name":"Resistor Color Code Calculator","category":"engineering","tool_name":"convert_resistor_color_code","description":"Decodes the colour bands of a 4-band or 5-band resistor (IEC 60062) into its resistance, tolerance and min/max values, or encodes a resistance value into the 4-band (or 5-band) colour sequence.","use_when":"You need to read a resistor's bands (band colours in, ohms out) or find the bands for a given resistance value.","do_not_use_when":"The part is an SMD resistor with a printed numeric code, a 6-band resistor (temperature coefficient band is ignored), or you need the resistor value for a circuit (use led-resistor or voltage-divider).","required_inputs":[],"optional_inputs":["band1","band2","band3","multiplier","tolerance","resistance_ohm"],"urls":{"html":"https://tttkmbb.com/engineering/resistor-color-code","markdown":"https://tttkmbb.com/engineering/resistor-color-code.md","schema":"https://tttkmbb.com/api/v1/calculators/resistor-color-code","api":"https://tttkmbb.com/api/v1/calculate/resistor-color-code"}},{"calculator_id":"rc-time-constant","entity_type":"calculator","name":"RC Time Constant Calculator","category":"engineering","tool_name":"calculate_rc_time_constant","description":"Computes the time constant τ = R·C of a resistor–capacitor circuit, the times to reach 63.2 %, 95 % and 99 % of the final voltage (and the 5τ 'full charge' convention), the −3 dB cutoff frequency 1/(2πRC), and optionally the charge level after a given time.","use_when":"You need how fast a capacitor charges or discharges through a resistor, or the corner frequency of a simple RC low-pass/high-pass filter.","do_not_use_when":"The circuit contains an inductor (use lc-resonance), the capacitor is driven by a constant-current source, or you only need the combined value of several capacitors (use capacitors-series-parallel).","required_inputs":["resistance_ohm","capacitance_uf"],"optional_inputs":["time_s"],"urls":{"html":"https://tttkmbb.com/engineering/rc-time-constant","markdown":"https://tttkmbb.com/engineering/rc-time-constant.md","schema":"https://tttkmbb.com/api/v1/calculators/rc-time-constant","api":"https://tttkmbb.com/api/v1/calculate/rc-time-constant"}},{"calculator_id":"capacitors-series-parallel","entity_type":"calculator","name":"Capacitors in Series and Parallel Calculator","category":"engineering","tool_name":"calculate_capacitors_series_parallel","description":"Computes the total capacitance of a list of capacitors 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rc-time-constant).","required_inputs":[],"optional_inputs":["inductance_uh","capacitance_pf","frequency_hz"],"urls":{"html":"https://tttkmbb.com/engineering/lc-resonance","markdown":"https://tttkmbb.com/engineering/lc-resonance.md","schema":"https://tttkmbb.com/api/v1/calculators/lc-resonance","api":"https://tttkmbb.com/api/v1/calculate/lc-resonance"}},{"calculator_id":"battery-runtime","entity_type":"calculator","name":"Battery Runtime Calculator","category":"engineering","tool_name":"estimate_battery_runtime","description":"Estimates how long a battery runs a load from its capacity (mAh, Ah or Wh), nominal voltage, the load in watts or amperes, and the usable depth of discharge (80 % for lithium-ion, 50 % for lead-acid by default).","use_when":"You want to know how many hours a power bank, UPS, solar or vehicle battery will supply a given load, or size a battery for a required runtime.","do_not_use_when":"The load is intermittent or very high-rate (Peukert losses reduce lead-acid capacity above the 20-hour rate), or you need charging time (use battery-charge-time).","required_inputs":[],"optional_inputs":["capacity_mah","capacity_ah","capacity_wh","voltage_v","load_w","load_a","battery_type","depth_of_discharge_percent"],"urls":{"html":"https://tttkmbb.com/engineering/battery-runtime","markdown":"https://tttkmbb.com/engineering/battery-runtime.md","schema":"https://tttkmbb.com/api/v1/calculators/battery-runtime","api":"https://tttkmbb.com/api/v1/calculate/battery-runtime"}},{"calculator_id":"battery-charge-time","entity_type":"calculator","name":"Battery Charge Time Calculator","category":"engineering","tool_name":"estimate_battery_charge_time","description":"Estimates the time to charge a battery from its capacity in Ah, the charger current, the charge efficiency (default 85 %) and the starting state of charge, and reports the charging C-rate.","use_when":"You need to know how long a phone, e-bike, car or solar battery takes to charge with a given charger current, or the C-rate that a charger imposes.","do_not_use_when":"You need the runtime of a battery under load (use battery-runtime) or an exact lithium-ion CC/CV profile (the constant-voltage tail makes the last 20 % slower than this linear estimate).","required_inputs":["capacity_ah","charge_current_a"],"optional_inputs":["charge_efficiency_percent","start_charge_percent"],"urls":{"html":"https://tttkmbb.com/engineering/battery-charge-time","markdown":"https://tttkmbb.com/engineering/battery-charge-time.md","schema":"https://tttkmbb.com/api/v1/calculators/battery-charge-time","api":"https://tttkmbb.com/api/v1/calculate/battery-charge-time"}},{"calculator_id":"wire-voltage-drop","entity_type":"calculator","name":"Wire Voltage Drop Calculator","category":"engineering","tool_name":"calculate_wire_voltage_drop","description":"Computes the resistance of a copper or aluminium conductor from its AWG gauge or cross-section and one-way length, then the voltage drop, percentage drop, voltage 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battery-runtime).","required_inputs":["panel_watts","peak_sun_hours_per_day"],"optional_inputs":["panel_count","performance_ratio","price_per_kwh"],"urls":{"html":"https://tttkmbb.com/engineering/solar-panel-output","markdown":"https://tttkmbb.com/engineering/solar-panel-output.md","schema":"https://tttkmbb.com/api/v1/calculators/solar-panel-output","api":"https://tttkmbb.com/api/v1/calculate/solar-panel-output"}},{"calculator_id":"decibel","entity_type":"calculator","name":"Decibel Calculator","category":"engineering","tool_name":"convert_decibels","description":"Converts between a linear ratio and decibels using 10·log10 for power quantities or 20·log10 for amplitude quantities (voltage, current, sound pressure), and between dBm and milliwatts (0 dBm = 1 mW).","use_when":"You need to express a gain, loss or signal ratio in dB, turn a dB figure back into a ratio, or convert an RF power level between dBm and mW/W.","do_not_use_when":"You need to add two sound levels or account for distance attenuation, or you need plain logarithms (use logarithm).","required_inputs":[],"optional_inputs":["quantity","linear_value","decibel_value"],"urls":{"html":"https://tttkmbb.com/engineering/decibel","markdown":"https://tttkmbb.com/engineering/decibel.md","schema":"https://tttkmbb.com/api/v1/calculators/decibel","api":"https://tttkmbb.com/api/v1/calculate/decibel"}},{"calculator_id":"horsepower-torque-rpm","entity_type":"calculator","name":"Horsepower, Torque and RPM Calculator","category":"engineering","tool_name":"solve_horsepower_torque_rpm","description":"Solves the rotational power relation for whichever of power, torque or rotational speed is missing (HP = torque_lb_ft × rpm / 5252; kW = torque_nm × rpm / 9549) and reports the results in hp, PS, kW, lb·ft and N·m.","use_when":"You know two of engine/motor power, torque and rpm (from a dyno sheet or a datasheet) and need the third, or want to convert a torque-at-rpm figure to horsepower.","do_not_use_when":"You only need a unit conversion of power (use power) or torque (use torque) without rpm, or you need road speed from rpm (use gear-ratio-speed).","required_inputs":[],"optional_inputs":["power_hp","power_kw","torque_lb_ft","torque_nm","rpm"],"urls":{"html":"https://tttkmbb.com/engineering/horsepower-torque-rpm","markdown":"https://tttkmbb.com/engineering/horsepower-torque-rpm.md","schema":"https://tttkmbb.com/api/v1/calculators/horsepower-torque-rpm","api":"https://tttkmbb.com/api/v1/calculate/horsepower-torque-rpm"}},{"calculator_id":"stopping-distance","entity_type":"calculator","name":"Stopping Distance Calculator","category":"engineering","tool_name":"calculate_stopping_distance","description":"Computes the reaction (thinking) distance, braking distance and total stopping distance of a vehicle from its speed, the driver's reaction time and either a road-condition friction coefficient or a given deceleration, in metres and feet.","use_when":"You want to know how far a car travels before it stops from a given speed on dry, wet, snowy or icy roads, or the effect of reaction time.","do_not_use_when":"You need the deceleration itself from speeds and times (use acceleration), or the energy dissipated in braking (use kinetic-energy).","required_inputs":["speed_km_h"],"optional_inputs":["reaction_time_s","road_condition","friction_coefficient","deceleration_m_s2"],"urls":{"html":"https://tttkmbb.com/engineering/stopping-distance","markdown":"https://tttkmbb.com/engineering/stopping-distance.md","schema":"https://tttkmbb.com/api/v1/calculators/stopping-distance","api":"https://tttkmbb.com/api/v1/calculate/stopping-distance"}},{"calculator_id":"engine-displacement","entity_type":"calculator","name":"Engine Displacement Calculator","category":"engineering","tool_name":"calculate_engine_displacement","description":"Computes engine displacement from bore, stroke and cylinder count (V = π/4 × bore² × stroke × cylinders) in cc, litres and cubic inches, plus the per-cylinder volume and bore/stroke ratio.","use_when":"You know an engine's bore and stroke and need its displacement, or want to check the effect of overboring or a stroker crank.","do_not_use_when":"You need the compression ratio (use compression-ratio) or a rotary/Wankel engine (displacement is defined differently).","required_inputs":["bore_mm","stroke_mm"],"optional_inputs":["cylinders"],"urls":{"html":"https://tttkmbb.com/engineering/engine-displacement","markdown":"https://tttkmbb.com/engineering/engine-displacement.md","schema":"https://tttkmbb.com/api/v1/calculators/engine-displacement","api":"https://tttkmbb.com/api/v1/calculate/engine-displacement"}},{"calculator_id":"compression-ratio","entity_type":"calculator","name":"Compression Ratio Calculator","category":"engineering","tool_name":"calculate_compression_ratio","description":"Computes the static compression ratio of a piston engine from bore, stroke, combustion chamber volume and the optional piston dish/dome, deck clearance and head gasket volumes: CR = (swept + clearance) / clearance.","use_when":"You are building or modifying an engine and need the compression ratio after changing heads, pistons, gaskets or deck height.","do_not_use_when":"You need dynamic (effective) compression ratio, which depends on intake valve closing timing, or plain displacement (use engine-displacement).","required_inputs":["bore_mm","stroke_mm","chamber_volume_cc"],"optional_inputs":["piston_volume_cc","deck_clearance_mm","head_gasket_thickness_mm","head_gasket_bore_mm"],"urls":{"html":"https://tttkmbb.com/engineering/compression-ratio","markdown":"https://tttkmbb.com/engineering/compression-ratio.md","schema":"https://tttkmbb.com/api/v1/calculators/compression-ratio","api":"https://tttkmbb.com/api/v1/calculate/compression-ratio"}},{"calculator_id":"tire-size","entity_type":"calculator","name":"Tire Size Calculator","category":"engineering","tool_name":"calculate_tire_size","description":"Parses a metric tire code such as 225/45R17 into section width, aspect ratio and rim size, computes sidewall height, overall diameter, circumference and revolutions per kilometre and mile, and optionally compares a second size (diameter difference and speedometer error).","use_when":"You want the dimensions of a tire from its sidewall code, or want to check whether an alternative size keeps the overall diameter (and speedometer) within a few percent.","do_not_use_when":"The tire uses a flotation size (31x10.50R15) or an old alphanumeric code, or you need road speed from rpm and gearing (use gear-ratio-speed).","required_inputs":["tire_code"],"optional_inputs":["compare_tire_code"],"urls":{"html":"https://tttkmbb.com/engineering/tire-size","markdown":"https://tttkmbb.com/engineering/tire-size.md","schema":"https://tttkmbb.com/api/v1/calculators/tire-size","api":"https://tttkmbb.com/api/v1/calculate/tire-size"}},{"calculator_id":"gear-ratio-speed","entity_type":"calculator","name":"Gear Ratio and Speed 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horsepower-torque-rpm).","required_inputs":["engine_rpm","gear_ratio","final_drive_ratio"],"optional_inputs":["tire_diameter_mm","tire_code","speed_km_h"],"urls":{"html":"https://tttkmbb.com/engineering/gear-ratio-speed","markdown":"https://tttkmbb.com/engineering/gear-ratio-speed.md","schema":"https://tttkmbb.com/api/v1/calculators/gear-ratio-speed","api":"https://tttkmbb.com/api/v1/calculate/gear-ratio-speed"}},{"calculator_id":"beam-deflection","entity_type":"calculator","name":"Beam Deflection Calculator","category":"engineering","tool_name":"calculate_beam_deflection","description":"Computes the maximum deflection, bending moment and shear force of a prismatic beam for four standard cases (simply supported with a mid-span point load or a uniform load, cantilever with an end point load or a uniform load) from span, load, elastic modulus and second moment of area, using the Euler–Bernoulli closed-form formulas.","use_when":"You need the mid-span or tip deflection of a steel, aluminium or timber beam under one point load or a uniformly distributed load, or want to check a deflection limit such as L/360.","do_not_use_when":"The beam carries several or off-centre loads, has overhangs, fixed ends or continuous supports (superpose cases or use structural software), or you need bending stress (divide the moment by the section modulus).","required_inputs":["beam_case","span_m","load","moment_of_inertia_cm4"],"optional_inputs":["elastic_modulus_gpa"],"urls":{"html":"https://tttkmbb.com/engineering/beam-deflection","markdown":"https://tttkmbb.com/engineering/beam-deflection.md","schema":"https://tttkmbb.com/api/v1/calculators/beam-deflection","api":"https://tttkmbb.com/api/v1/calculate/beam-deflection"}},{"calculator_id":"pipe-flow","entity_type":"calculator","name":"Pipe Flow Calculator (Hazen–Williams)","category":"engineering","tool_name":"calculate_pipe_flow_hazen_williams","description":"Computes the flow velocity, friction head loss and pressure drop of water in a full-flowing round pipe from flow rate, internal diameter, length and the Hazen–Williams roughness coefficient C, plus an estimated Reynolds number and a velocity check.","use_when":"You are sizing a water supply, irrigation, fire-protection or pump discharge line and need the friction loss for a given flow, or want to check that the velocity stays in the usual 0.6–2.5 m/s range.","do_not_use_when":"The fluid is not water at ordinary temperature (oil, gas, glycol mixtures: use Darcy–Weisbach with the fluid's viscosity), flow is laminar, or the pipe is partly full (open-channel flow).","required_inputs":["flow_rate","pipe_diameter_mm","pipe_length_m"],"optional_inputs":["flow_unit","hazen_williams_c"],"urls":{"html":"https://tttkmbb.com/engineering/pipe-flow","markdown":"https://tttkmbb.com/engineering/pipe-flow.md","schema":"https://tttkmbb.com/api/v1/calculators/pipe-flow","api":"https://tttkmbb.com/api/v1/calculate/pipe-flow"}},{"calculator_id":"horizontal-tank-volume","entity_type":"calculator","name":"Horizontal Tank Volume Calculator","category":"engineering","tool_name":"calculate_horizontal_tank_volume","description":"Computes the liquid volume in a horizontal cylindrical tank from its diameter, length and the measured liquid depth, using the circular-segment area for flat ends and adding two spherical-cap segments for hemispherical ends, plus total capacity, fill percentage and remaining ullage.","use_when":"You need to convert a dipstick or sight-glass reading on a horizontal fuel, water, oil or chemical tank into litres or gallons, or want the tank's total capacity.","do_not_use_when":"The tank stands vertically or is rectangular (volume is simply area × depth; use cylinder or rectangular-prism), has dished or elliptical (2:1) heads, or is not level.","required_inputs":["diameter_m","length_m","liquid_level_m"],"optional_inputs":["end_type"],"urls":{"html":"https://tttkmbb.com/engineering/horizontal-tank-volume","markdown":"https://tttkmbb.com/engineering/horizontal-tank-volume.md","schema":"https://tttkmbb.com/api/v1/calculators/horizontal-tank-volume","api":"https://tttkmbb.com/api/v1/calculate/horizontal-tank-volume"}},{"calculator_id":"timer-555","entity_type":"calculator","name":"555 Timer Calculator","category":"engineering","tool_name":"calculate_555_timer","description":"Computes the output frequency, period, high and low times and duty cycle of a 555 timer in astable (oscillator) mode from R1, R2 and C, or the pulse width of the monostable (one-shot) mode from R and C, using the equations of the NE555 datasheet.","use_when":"You are choosing resistor and capacitor values for a 555 oscillator, LED blinker, PWM source or one-shot pulse and need the resulting frequency, duty cycle or pulse duration.","do_not_use_when":"The circuit uses a diode across R2 or a separate control-voltage input (different timing), a CMOS 555 at very high frequency where propagation delay matters, or you need an RC filter or charging time (use rc-time-constant).","required_inputs":["mode","c_microfarads"],"optional_inputs":["r1_ohms","r2_ohms","r_ohms"],"urls":{"html":"https://tttkmbb.com/engineering/timer-555","markdown":"https://tttkmbb.com/engineering/timer-555.md","schema":"https://tttkmbb.com/api/v1/calculators/timer-555","api":"https://tttkmbb.com/api/v1/calculate/timer-555"}},{"calculator_id":"op-amp-gain","entity_type":"calculator","name":"Op-Amp Gain Calculator","category":"engineering","tool_name":"calculate_op_amp_gain","description":"Computes the voltage gain (as a ratio and in dB) of the four basic operational-amplifier circuits from the feedback and input resistors, and optionally the output voltage for a given input, clipped to the supply rails.","use_when":"You are designing or checking an op-amp stage and need the gain from resistor values, the resistor ratio for a target gain, or the expected output voltage and whether it will saturate.","do_not_use_when":"Frequency response, bandwidth or slew-rate limits matter (this is the ideal DC gain), the circuit is a filter, integrator or instrumentation amplifier, or you only need a passive divider (use voltage-divider).","required_inputs":["configuration"],"optional_inputs":["feedback_resistor_ohms","input_resistor_ohms","input_voltage_v","second_input_voltage_v","supply_voltage_v"],"urls":{"html":"https://tttkmbb.com/engineering/op-amp-gain","markdown":"https://tttkmbb.com/engineering/op-amp-gain.md","schema":"https://tttkmbb.com/api/v1/calculators/op-amp-gain","api":"https://tttkmbb.com/api/v1/calculate/op-amp-gain"}},{"calculator_id":"antenna-length","entity_type":"calculator","name":"Antenna Length Calculator","category":"engineering","tool_name":"calculate_antenna_length","description":"Computes the free-space wavelength for a frequency and the physical wire length of a half-wave dipole (with the length of each leg), a quarter-wave vertical, a full-wave loop or a 5/8-wave radiator, applying a velocity (end-effect) factor as in the 468/f ft rule.","use_when":"You are cutting wire or tubing for an amateur-radio, CB, FM, Wi-Fi, LoRa or ISM-band antenna and need the starting length for a given frequency.","do_not_use_when":"You need a Yagi, patch, helical or loaded (shortened) antenna design, impedance matching, or just the wavelength without an antenna (use wavelength-frequency).","required_inputs":["frequency_mhz"],"optional_inputs":["antenna_type","velocity_factor"],"urls":{"html":"https://tttkmbb.com/engineering/antenna-length","markdown":"https://tttkmbb.com/engineering/antenna-length.md","schema":"https://tttkmbb.com/api/v1/calculators/antenna-length","api":"https://tttkmbb.com/api/v1/calculate/antenna-length"}},{"calculator_id":"kva-kw-power-factor","entity_type":"calculator","name":"kVA, kW and Power Factor Calculator","category":"engineering","tool_name":"convert_kva_kw_power_factor","description":"Completes the AC power triangle from any two of apparent power (kVA), real power (kW), reactive power (kVAR) and power factor, reports the phase angle and, when a voltage is given, the single- or three-phase line current, plus the capacitor kVAR needed to correct the power factor to 0.95.","use_when":"You need to convert a transformer, generator or UPS kVA rating to usable kW, find the power factor or reactive power of a load, size a power-factor-correction capacitor bank, or get the current for a kVA load at a voltage.","do_not_use_when":"You have line voltage and current of a balanced three-phase load and want the full per-phase breakdown (use three-phase-power), or the load is DC or non-sinusoidal with strong harmonics (displacement and distortion power factor differ).","required_inputs":[],"optional_inputs":["apparent_power_kva","real_power_kw","power_factor","reactive_power_kvar","voltage_v","phases"],"urls":{"html":"https://tttkmbb.com/engineering/kva-kw-power-factor","markdown":"https://tttkmbb.com/engineering/kva-kw-power-factor.md","schema":"https://tttkmbb.com/api/v1/calculators/kva-kw-power-factor","api":"https://tttkmbb.com/api/v1/calculate/kva-kw-power-factor"}},{"calculator_id":"three-phase-power","entity_type":"calculator","name":"Three-Phase Power Calculator","category":"engineering","tool_name":"calculate_three_phase_power","description":"Computes real, apparent and reactive power of a balanced three-phase load from line voltage, line current and power factor, or the line current needed for a given real power, and reports the phase voltage and phase current for wye (star) or delta connection.","use_when":"You need the power drawn by a three-phase motor, heater or feeder from its current, the full-load current for a given kW, or the per-phase voltage and current for a wye or delta winding.","do_not_use_when":"The load is unbalanced (compute each phase separately), single-phase (use kva-kw-power-factor or electric-power), or you only know kVA and power factor without a voltage (use kva-kw-power-factor).","required_inputs":["mode"],"optional_inputs":["line_voltage_v","current_a","real_power_kw","power_factor","connection"],"urls":{"html":"https://tttkmbb.com/engineering/three-phase-power","markdown":"https://tttkmbb.com/engineering/three-phase-power.md","schema":"https://tttkmbb.com/api/v1/calculators/three-phase-power","api":"https://tttkmbb.com/api/v1/calculate/three-phase-power"}}]},"timestamp":"2026-09-24T01:52:11Z","next_actions":[],"links":{"docs":"https://tttkmbb.com/calculators.md"}}