Power & Electrical
Basic Voltage Drop Calculator
Estimate voltage drop from current, run length, resistance per metre and supply voltage.
Basic estimate only. Real cable design depends on installation method, temperature, grouping, conductor material and local regulations.
Notes and next steps
How it works
Estimate voltage drop from current, run length, supply voltage and resistance per metre.
Formula used: Voltage drop = current × length × resistance per metre. Percentage = drop ÷ supply voltage × 100.
Worked example
20 A × 25 m × 0.0073 Ω/m = 3.65 V drop, about 1.59% of 230 V.
Common mistakes
- Using the wrong resistance value.
- Forgetting installation method and temperature.
- Treating a basic estimate as final design.