Ohm's Law Calculator

How it works

Ohm’s law relates voltage, current and resistance; the power law adds dissipated power. Any two of the four quantities fix the other two:

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

From power and resistance alone, the calculator takes a square root: V = √(P × R) and I = √(P / R).

Inputs

• Type in any two fields. The two fields you edited last are the inputs; the other two are computed and shown dimmed.
• SI prefixes work everywhere: p n u (µ) m k M G T. Resistor notation works too: 4k7 = 4.7 kΩ, 2R2 is not supported yet.
• A trailing unit is ignored, so 12V and 20mA are fine.

Assumptions and limits

• DC, or AC RMS values with a purely resistive load. Reactive loads need impedance and power factor.
• Results are rounded to 4 significant digits for display; copy gives the same rounded value.

References

• Ohm’s law — Wikipedia