About voltage calculator
Voltage is the electrical pressure that pushes current through a circuit. You can find it from current and resistance or from power and current.
Formulas
- V = I × R.
- V = P ÷ I.
Example
A device drawing 0.5 A through a 20 Ω resistor drops 10 V. A 60 W lamp drawing 0.26 A is on roughly 230 V.
Another worked example
A 15 Ω resistor carrying 2 A has a voltage across it of 15 × 2 = 30 V. A device that uses 100 W while drawing 0.5 A must be on 100 ÷ 0.5 = 200 V.
Voltage drop
Long, thin cables lose some voltage as current flows, so a device far from the supply may receive less than the nominal voltage. Use a thicker cable for long runs.
