What this calculator does
Ohm’s law works out voltage, current, resistance and power from any two. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaV = I·R · P = V·I = I²R = V²/R
The inputs explained
| Field | What to enter |
|---|---|
| Known quantity 1 | A number. Starts at 12. |
| is | Choose from Voltage (V), Current (A), Resistance (Ω), Power (W). |
| Known quantity 2 | A number. Starts at 0.5. |
| is | Choose from Voltage (V), Current (A), Resistance (Ω), Power (W). |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with known quantity 1
Every other input is held at the calculator’s starting values while known quantity 1 varies. Select any row to load that scenario into the calculator.