Does it pick a standard cable size for me?

No. It returns the required area and evaluates the candidate you enter. Selecting the next standard size from a manufacturer table remains your decision.

Is this an IEC/NEC compliance check?

No. It is a preliminary, criteria-driven calculation. No code table, installation-method factor or protection coordination rule is embedded.

What does the margin percentage mean?

It is how far the derated ampacity exceeds the design current, so you can see whether the candidate cable is comfortable or marginal.

ProfessionalAvailable now

Cable Sizing

Determine cable sizes from defined inputs.

Electrical Design SuiteStep 3 of 6

This calculator is part of a paid level

Unlock this calculator with a single purchase; access stays on your account for life.

View levels and pricing Free calculators in this category

A cable has to satisfy two independent checks: enough cross-section for the voltage drop you allow, and enough derated current-carrying capacity for the design current. This tool performs both in one pass using your own resistivity, derating factor and candidate ampacity.

Method and assumptions

S(mm²) = k × I × L × ρ ÷ ΔV_allowed, k=2 single-phase, k=√3 three-phase
Derated ampacity = candidate × derating%
Margin% = (derated − I_design) ÷ I_design × 100

The candidate ampacity and derating factor are taken from the user's own approved supplier table or code, never assumed.
A preliminary decision-support estimate: the result does not replace an approved design calculation or review by a competent authority.
All percentages and inputs are user-defined; the calculation is purely arithmetic and assumes no particular code or specification.

Frequently asked questions

Does it pick a standard cable size for me?: No. It returns the required area and evaluates the candidate you enter. Selecting the next standard size from a manufacturer table remains your decision.
Is this an IEC/NEC compliance check?: No. It is a preliminary, criteria-driven calculation. No code table, installation-method factor or protection coordination rule is embedded.
What does the margin percentage mean?: It is how far the derated ampacity exceeds the design current, so you can see whether the candidate cable is comfortable or marginal.

Next step

Free calculators are open to everyone. Project saving and PDF/Excel reports come with Professional, and integrated workflows with Premium.