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Ohm's Law Calculator

Solves Ohm's law V = I·R for whichever of voltage, current or resistance is omitted and reports the electrical power dissipated (P = V·I).

When to use

You know two of voltage, current and resistance in a DC or purely resistive circuit and need the third and the power.

Do not use when: The load is reactive (inductors or capacitors require impedance, not resistance), you want energy cost over time (use electric-power), or you need the equivalent resistance of several resistors (use resistors-series-parallel).

Formula

V = I × R; I = V / R; R = V / I; P = V × I = I² × R = V² / R

Inputs

Parameter	Type	Unit	Required	Description
`voltage_v`	number	V	no	Potential difference across the component in volts. Omit to solve for it. Range: ≥ 0
`current_a`	number	A	no	Current through the component in amperes (1 mA = 0.001 A). Omit to solve for it. Range: ≥ 0
`resistance_ohm`	number	Ω	no	Resistance in ohms (1 kΩ = 1000 Ω). Omit to solve for it. Range: > 0

Outputs

Output	Type	Unit	Description
`solved_for`	string		Which quantity was computed: voltage_v, current_a or resistance_ohm.
`voltage_v`	number	V	V = I × R.
`current_a`	number	A	I = V / R.
`current_ma`	number	mA	Current in milliamperes.
`resistance_ohm`	number	Ω	R = V / I.
`power_w`	number	W	Power dissipated P = V × I.

Example

12 V across 220 Ω: {"voltage_v":12,"resistance_ohm":220} → {"solved_for":"current_a","current_a":0.054545,"current_ma":54.545,"power_w":0.6545}

2 A through 50 Ω: {"current_a":2,"resistance_ohm":50} → {"solved_for":"voltage_v","voltage_v":100,"power_w":200}

GET https://tttkmbb.com/api/v1/calculate/ohms-law?voltage_v=12&resistance_ohm=220

Machine access

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

Sources

HyperPhysics – Ohm's law (reference)
Wikipedia – Ohm's law (reference)

FAQ

Does Ohm's law apply to AC circuits?

Only for purely resistive loads. With inductance or capacitance the relation becomes V = I·Z with complex impedance Z, and the power depends on the phase angle.

Why does the power matter?

A resistor must be rated above the dissipated power (e.g. 0.65 W needs at least a 1 W resistor) or it overheats.

Related calculators

Electric Power Calculator — Power, energy and running cost of an appliance.
Resistors in Series and Parallel Calculator — Equivalent resistance of several resistors.