Ohm's Law Calculator

The formula this calculator uses

V = I x R

V

Voltage — the potential difference across the component, in volts

I

Current — the rate of charge flow through it, in amperes

R

Resistance — how strongly it opposes the flow, in ohms

P

Power — the rate of energy dissipation, in watts

How to check the result by hand

1. 1

   Identify which two quantities you actually know

   Ohm's law needs two of voltage, current and resistance. Write down the values you were given and mark the one you want, so the rearrangement is chosen rather than guessed.

2. 2

   Convert every value to base units first

   Turn milliamperes into amperes and kilohms into ohms before substituting. 3 milliamperes becomes 0.003 amperes; skipping this step is the source of most factor-of-a-thousand errors.

3. 3

   Apply the matching rearrangement

   Use I = V / R when you want current, R = V / I when you want resistance, and V = I x R when you want voltage. For 12 volts and 6 ohms, the current is 12 / 6 = 2 amperes.

4. 4

   Cross-check with the power forms

   Compute P = V x I, then confirm it against I^2 x R and V^2 / R. All three should give 24 watts here; a disagreement points to a slip in the earlier step.

5. 5

   Sanity-check the magnitude and the rating

   Ask whether the current is plausible for the circuit and whether the dissipated power sits inside the component's rating. A resistor that is correct on paper can still overheat in practice.