Calculator for Ohm's Law

Formula

V = I × R, and P = V × I. From those two, all other forms follow: I = V ÷ R, R = V ÷ I, P = I² × R, P = V² ÷ R. The Check chip dey calculate the answer again through the other relation to confirm say both agree.

Example wey show the calculation

To find current with V = 12 V and R = 4 Ω: I = V ÷ R = 12 ÷ 4 = 3.00 A. Power = V × I = 12 × 3 = 36.00 W. Check with the other form: P = V² ÷ R = 144 ÷ 4 = 36.00 W. Both agree.

Where e fit work and limits

This one cover DC and resistive AC. E assume say voltage and current dey in phase and resistance remain constant. E no cover reactive AC circuits (inductors, capacitors and phase shift) or resistance wey change with temperature. Filament lamp resistance dey rise sharply as e hot, so cold resistance fit give wrong current estimate. Zero resistance na short circuit: ideal model get no bounded current, so the page no divide by zero or show infinity. Real circuits get some resistance and supply wey get current limit.

Version of di formula: 7b0965da4757 · Example don get check: 2026-10-31

Questions wey people dey ask often

Which two values I need?

If you know any two of voltage, current and resistance, you fit find the third. Power go follow from voltage and current. Choose the unknown above and enter the two wey you know.

Why the page no accept zero resistance?

Na because I = V ÷ R with R = 0 na short circuit. Ideal model predict infinite current. Real power supplies go limit current or fail. No finite answer dey, so the page dey explain am.

This one work for AC mains?

For resistive loads like heaters and incandescent lamps, yes: use RMS voltage and current. For motors or electronics wey get inductance or capacitance, use impedance and calculations wey account for phase instead.

Wetin the power rating warning mean?

Resistor dey turn power to heat. A result of 36 W through a 0.25 W resistor fit destroy am. Always compare calculated power with the component power rating; no check only resistance value.

Volts, amps, ohms: which unit scale I suppose use?

We dey use base SI units: volts, amps, ohms and watts. For milliamps, divide by 1,000 first (500 mA = 0.5 A). For kilohms, multiply by 1,000 (4.7 kΩ = 4700 Ω).

I fit calculate power directly?

Yes. Choose Power, then enter voltage and current. The page dey show the implied resistance (V ÷ I) as check value too.

Other tools wey relate to dis

• Calculator for electricity cost — cost of the power wey a device dey use over time
• Tool to convert length units — milliamps, kilohms and other unit scales
• Converter for temperature — how resistance dey change with temperature