Calculating your resistance (r) is straightforward once you know the Ohm's Law formula and what each input means. This guide explains the method in plain language, walks through a manual calculation, and gives worked examples you can follow — then you can do it instantly with the Ohm's Law Calculator.
What is Ohm's Law?
The Ohm's Law calculation tells you your resistance (r) from a few simple inputs. The figure you are solving for here is the resistance (r).
The Ohm's Law formula
The core formula is:
Resistance (R) = Voltage (V) ÷ Current (I)Here is what each input means:
- Voltage (V) — a value measured in V. Example: 12 V.
- Current (I) — a value measured in A. Example: 2 A.
How to calculate it step by step
- Write down the voltage (v) (for example, 12 V).
- Write down the current (i) (for example, 2 A).
- Apply the formula above to get your resistance (r).
- Double-check the result with the Ohm's Law Calculator.
Worked examples
Example 1
| Input / Output | Value |
|---|---|
| Voltage (V) | 12 V |
| Current (I) | 2 A |
| Resistance (R) | 6.000 |
| Power (P) | 24.000 |
With voltage (v) of 12 V and current (i) of 2 A, the resistance (r) works out to 6.000.
Example 2
With voltage (v) of 24 V and current (i) of 2 A, the resistance (r) works out to 12.000.
| Result | Value |
|---|---|
| Resistance (R) | 12.000 |
| Power (P) | 48.000 |
Example 3
With voltage (v) of 6 V and current (i) of 2 A, the resistance (r) works out to 3.000.
| Result | Value |
|---|---|
| Resistance (R) | 3.000 |
| Power (P) | 12.000 |
Tips for an accurate result
- Keep your units consistent — mixing, say, months with years or grams with kilograms is the most common source of error.
- Round only at the very end. Rounding inputs early can shift the final answer noticeably.
- Re-run the numbers whenever an input changes, rather than estimating from an old result.
Prefer not to do the maths by hand? — the Ohm's Law Calculator does it instantly, for free, with the formula and a worked example built in.
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