Wire size calculator by voltage drop
Set the length, current, voltage and allowed drop, and the tool suggests the standard size, which matters most on long runs.
Loading the tool…
Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter supply type, conductor, one-way cable length, current, supply voltage and maximum allowed drop.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
A = k × L × I × ρ ÷ (V × drop% ÷ 100), with k = 2 for DC and single-phase and √3 for three-phase; then the first standard size at or above A is chosen.
Example
Inputs: Supply type = AC single-phase, Conductor = Copper, One-way cable length = 30 m, Current = 16 A, Supply voltage = 230 V. Result: Suggested standard size: 2.5 mm²; Minimum calculated area: 2.399 mm²; Actual drop with standard size: 6.621 V.
Limits and caveats
- Sizes by voltage drop only and does not check current-carrying capacity (ampacity) or short-circuit rating; check those against IEC 60364-5-52 or your local code and use the larger size.
- Ignores reactance, which matters for large cables.
Questions about this tool
Is this size enough to carry the current?
Not necessarily. This tool only guarantees the voltage drop; the current may need a larger size depending on installation method and ambient heat.
What are the standard cable sizes?
Per IEC 60228: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120 mm² and up.
What percentage should I enter?
3% is common for final circuits; some codes allow up to 5% from the origin to the load.