Ohm's Law Calculator
Fill in any two of the four values and leave the others empty.
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The formulas
- Ohm's law: V = I × R, so I = V ÷ R and R = V ÷ I.
- Power: P = V × I = I² × R = V² ÷ R.
With any two of the four quantities, the other two can be found.
Examples
- An LED circuit: 12 V across a 220 Ω resistor gives 12 ÷ 220 = 0.0545 A (54.5 mA) and 0.65 W, so a 1-watt resistor is needed, not the common ¼-watt one.
- A 1,000 W kettle on 230 V draws 4.35 A and has a resistance of about 53 Ω when hot.
Safety
Choose resistors and wires rated above the power and current you calculate. Mains electricity (230 V in Pakistan) is dangerous: use this for learning and low-voltage electronics, and have house wiring done by a qualified electrician. For alternating current with motors or capacitors, real power also depends on the power factor.
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How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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