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Cable Size Calculator

Estimate AWG cable size from amps, voltage, run length, conductor material, derating factors, voltage drop, and simplified ampacity limits.

Published

Voltage drop
Voltage drop
3.09 V
Voltage drop percentage
2.57%

Arithmetic worksheet only. Enter resistance from the conductor manufacturer; this does not size conductors or determine ampacity or code compliance.

V
A
ft
Ω/1000 ft

Results update as you type.

Cable Size Calculator

Estimate AWG cable size from amps, voltage, run length, conductor material, derating factors, voltage drop, and simplified ampacity limits.

Inputs and method

Enter voltage, current, one-way run length, and candidate-conductor resistance in ohms per 1,000 feet. For a two-conductor path, voltage drop is 2 × current × resistance × one-way length ÷ 1,000; percentage drop divides that result by system voltage.

Calculations retain full floating-point precision until the labeled display step. Counts and packages use an explicit upward ceiling only where a whole purchase unit is required.

Interpreting the estimate

Use the result as a planning value and keep input precision consistent with the measurements or source data you have. Small displayed differences can come from final-place rounding; intermediate values are not rounded.

Assumptions and limits

This worksheet does not choose wire size, determine ampacity, or establish electrical-code compliance. Obtain resistance from current manufacturer data and have electrical work designed and checked for the applicable installation.

Empty or invalid inputs, prohibited negatives, zero denominators, impossible relationships, and unsupported options do not produce a potentially misleading numeric result.

Sources

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Cable Size Calculator updated at