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Electric Power Calculator

Computes electrical power from voltage and current (or the current drawn by a known power at a given voltage), the equivalent resistance, and, with hours of use and a tariff, the energy in kWh and its cost.

When to use

You need the wattage or amperage of an appliance, whether it fits a circuit rating, or how much energy and money it uses over a period.

Do not use when: The load has a power factor below 1 (motors, some electronics: P = V·I·cos φ), you only need V, I and R relations (use ohms-law), or you want a multi-appliance bill (use electricity-cost).

Formula

power_w = voltage_v × current_a (or current_a = power_w / voltage_v); resistance_ohm = voltage_v / current_a; energy_kwh = power_w × usage_hours / 1000; energy_cost = energy_kwh × price_per_kwh

Inputs

Parameter	Type	Unit	Required	Description
`voltage_v`	number	V	yes	Supply voltage in volts (e.g. 230 in Europe, 120 in North America, 12 for automotive). Range: > 0
`current_a`	number	A	no	Current drawn in amperes. Give either current_a or power_w. Range: ≥ 0
`power_w`	number	W	no	Rated power in watts. Give either current_a or power_w. Range: ≥ 0
`usage_hours`	number	h	no	Optional operating time; enables the energy output. Range: ≥ 0
`price_per_kwh`	number	per kWh	no	Optional tariff in your currency per kilowatt-hour; enables the cost output. Range: ≥ 0

Outputs

Output	Type	Unit	Description
`power_w`	number	W	P = V × I.
`power_kw`	number	kW	Power in kilowatts.
`current_a`	number	A	I = P / V.
`resistance_ohm`	number	Ω	R = V / I for a purely resistive load.
`energy_kwh`	number	kWh	P × usage_hours / 1000 (only when usage_hours is given).
`energy_cost`	number		energy_kwh × price_per_kwh (only when usage_hours and price_per_kwh are given).

Example

230 V, 6.5 A for 2 h at 0.30 per kWh: {"voltage_v":230,"current_a":6.5,"usage_hours":2,"price_per_kwh":0.3} → {"power_w":1495,"power_kw":1.495,"current_a":6.5,"resistance_ohm":35.3846,"energy_kwh":2.99,"energy_cost":0.9}

1500 W heater on 120 V: {"voltage_v":120,"power_w":1500} → {"power_w":1500,"current_a":12.5,"resistance_ohm":9.6}

GET https://tttkmbb.com/api/v1/calculate/electric-power?voltage_v=230&current_a=6.5&usage_hours=2&price_per_kwh=0.3

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/electric-power (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/electric-power · Markdown: https://tttkmbb.com/physics/electric-power.md · JSON definition: https://tttkmbb.com/physics/electric-power.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="electric-power"
OpenAPI operationId: calculate_electric_power
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

HyperPhysics – Electric power (reference)
Wikipedia – Electric power (reference)

FAQ

Is the nameplate wattage the actual consumption?

It is the maximum rating. Thermostat-controlled appliances (heaters, fridges) draw it only part of the time, so real energy use is lower.

What about three-phase or AC loads?

For single-phase AC the formula gives apparent power (VA); real power is V·I·cos φ. Three-phase power is √3 × V_line × I × cos φ and is not covered here.

Related calculators

Ohm's Law Calculator — Voltage, current and resistance relations.
Electricity Cost Calculator — Running cost of several appliances over a period.
Work & Power Calculator — Mechanical power from work and time.