BYTETOOLS

Ohm's Law Calculator

Solve Ohm's law online: enter any two of voltage, current, resistance or power and get the other two instantly, with mV, mA, kΩ and kW unit prefixes.

12 V
Voltage
2 A
Current
6 Ω
Resistance
24 W
Power

How it was solved

Derived with I = V ÷ R and P = V² ÷ Rfrom Ohm's law (V = I × R) and the power law (P = V × I).

What is the Ohm's Law Calculator?

The ByteTools Ohm's Law Calculator solves the classic V–I–R–P wheel. Pick any two known quantities — voltage, current, resistance or power — and the calculator derives the remaining two from V = I × R and P = V × I.

  • Solves any pair: V&I, V&R, V&P, I&R, I&P or R&P
  • Unit prefixes for every quantity (m, k, M)
  • Shows the exact formula used for each derived value
  • Power dissipation always included
  • Guards against divide-by-zero and negative inputs
  • 100% private — runs entirely in your browser

How to use the Ohm's Law Calculator

  1. 1

    Choose which two quantities you know (for example voltage and resistance).

  2. 2

    Enter each value and pick its unit prefix (mV, V, kV, mA, A, mΩ, Ω, kΩ, MΩ…).

  3. 3

    Read the other two quantities, derived from V = IR and P = VI.

  4. 4

    Check the formulas shown under the result to see how each value was computed.

  5. 5

    Click Copy to grab all four values.

About the Ohm's Law Calculator

The ByteTools Ohm's Law Calculator solves the classic V–I–R–P wheel. Pick any two known quantities — voltage, current, resistance or power — and the calculator derives the remaining two from V = I × R and P = V × I. Unit prefixes are handled for you, so you can mix millivolts, kilohms, milliamps and watts freely.

It is built for electronics hobbyists, electricians, and physics students checking circuit values before touching a soldering iron. The exact formula used for each derived quantity is printed under the result, so you can follow the algebra rather than just trusting a number.

Everything is computed instantly with JavaScript, 100% locally in your browser. No values are uploaded or stored anywhere, so the calculator is private, works offline, and never sends your circuit details to a server.

Frequently asked questions

What is Ohm's law?

Ohm's law states that the current through a conductor is proportional to the voltage across it: V = I × R, where V is voltage in volts, I is current in amps and R is resistance in ohms. Combined with the power law P = V × I, any two of the four quantities determine the other two.

How do I calculate resistance from voltage and current?

Divide voltage by current: R = V ÷ I. For example, a 12 V supply pushing 2 A through a load means the load resistance is 12 ÷ 2 = 6 Ω. The calculator does this automatically and also reports the power, P = 12 × 2 = 24 W.

How is power calculated from resistance?

If you know voltage and resistance, power is P = V² ÷ R. If you know current and resistance, it is P = I² × R. The calculator picks the right variant for whichever pair you entered and shows the formula it used.

Does Ohm's law work for all components?

It holds for ohmic components such as resistors and most wiring at constant temperature. Diodes, LEDs, filament bulbs and other non-linear devices do not follow a fixed V/I ratio, so for those the calculated resistance is only valid at that specific operating point.

Can I use AC values in this calculator?

Yes, for purely resistive AC circuits using RMS voltage and current the same formulas apply. For circuits with significant inductance or capacitance you need impedance and power factor, which this simple resistive calculator does not model.

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