Wire ampacity calculator

Apply supplied correction factors to a table ampacity and compare the result with your termination limit.

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Base ampacity from applicable table (amps)

Applicable temperature correction factor

More inputs and assumptions

Applicable conductor grouping factor

Termination or equipment current limit (amps)

Answer

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Apply supplied correction factors to a table ampacity and compare the result with your termination limit.

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Precision and calculation record

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Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

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Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Adjusted table ampacity is base amps times both entered factors; the result is capped by the supplied termination or equipment limit. Example inputs are an arithmetic scenario, not code-table recommendations. Obtain every value from the applicable wiring code, conductor insulation rating, installation conditions and equipment instructions. This page does not select wire size, breaker rating or a compliant circuit; additional rules and limits may apply.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-29

Using Wire ampacity calculator

Apply supplied correction factors to a table ampacity and compare the result with your termination limit.

Next: Wire size calculator

Next: Voltage drop calculator

A worked example

For base ampacity from applicable table (amps) = 40, applicable temperature correction factor = 0.91, applicable conductor grouping factor = 0.8, termination or equipment current limit (amps) = 35, lower calculated limit (amps) = 29.12.

Before you use the result

Example results for base ampacity from applicable table (amps)

These examples use Applicable temperature correction factor: 0.91; Applicable conductor grouping factor: 0.8; Termination or equipment current limit (amps): 35. They are reference calculations, not recommended settings.

Base ampacity from applicable table (amps)	Lower calculated limit (amps)
20	14.56
40	29.12
80	35

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