About ohm's law calculator
Ohm's law links voltage, current and resistance in a circuit: V = I × R. Enter any two of the values (including power) and the tool finds the others.
Formulas
- Voltage V = I × R.
- Current I = V ÷ R.
- Resistance R = V ÷ I.
- Power P = V × I, which also equals I² × R and V² ÷ R.
Example
A 12 V supply across a 6 Ω resistor gives 2 A of current and 24 W of power.
Safety
Calculations do not replace safe practice. Mains electricity is dangerous; have a qualified electrician do wiring work.
Another worked example
A heater connected to 230 V draws 5 A. By Ohm's law its resistance is 230 ÷ 5 = 46 Ω and its power is 230 × 5 = 1,150 W. If you only know the power and the voltage, the current is 1,150 ÷ 230 = 5 A.
Remember
Ohm's law applies to resistive loads. Motors and electronics have more complex behaviour, so their ratings on the label are the better guide.
