About Cable Size Calculator

CableSizeCalculator.com is a small set of free tools built to answer one practical question quickly: what cable size do I actually need for this load, distance and voltage?

How the calculators work

Each tool runs two checks, current-carrying capacity (ampacity) and voltage drop, against standard published reference tables and formulas, then recommends the larger of the two resulting sizes. The ampacity figures are modelled on commonly published NEC (NFPA 70, Table 310.16) and general IEC-style conductor tables; the voltage-drop calculation uses standard copper and aluminium resistivity values. AWG and mm² sizes are converted using the standard AWG geometric formula rather than a fixed lookup table, so the converter works for any size, not just a short list.

These are simplified, general-purpose references. They can't capture every local code amendment, unusual installation method, or manufacturer-specific de-rating, so we're explicit about that on every results panel: use this as a fast first estimate, then confirm against your local electrical code and, for anything beyond a small DIY task, a licensed electrician.

Where we're heading

We're expanding coverage of specific, genuinely different sizing scenarios: motor and industrial feeder tables, conduit fill, and standards-specific views (NEC vs. IEC vs. BS 7671), rather than duplicating the same calculator under lots of near-identical page titles. Three-phase AC sizing is already live on the three-phase calculator. If there's a specific sizing scenario you'd like to see covered, let us know.

Spotted an error?

If a result looks wrong, or you know of a more accurate reference value we should be using, please get in touch. We'd rather fix it than leave it.