Ohm's law calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- Ohm's law: V = I × R. Power: P = V × I = I² × R = V² ÷ R.
- With the two values you entered, the other two follow from these formulas.
| Inputs | Answer |
|---|---|
| Voltage V: 12; Current I: 2; Resistance R: ; Power P: | V = 12 volts, I = 2 amps, R = 6 ohms, P = 24 watts. |
| Voltage V: 230; Current I: ; Resistance R: 46; Power P: | V = 230 volts, I = 5 amps, R = 46 ohms, P = 1,150 watts. |
| Voltage V: ; Current I: 5; Resistance R: ; Power P: 1200 | V = 240 volts, I = 5 amps, R = 48 ohms, P = 1,200 watts. |
How to use it
Ohm's law relates voltage V, current I and resistance R: V = I × R. Power is P = V × I, which also equals I² × R and V² ÷ R. Enter any two of the four quantities and the calculator works out the other two: 12 V and 2 A give 6 Ω and 24 W.
The formulas apply to resistive DC circuits; AC circuits with reactance and power factor need more.
Frequently asked questions
What is Ohm's law?
Voltage equals current times resistance (V = I × R).
How do I find power?
Multiply voltage by current (P = V × I).
What if I know power and resistance?
V = √(P × R) and I = √(P ÷ R); the calculator does this for you.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
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General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.