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Extension Cord Gauge Calculator

Voltage drop on a 120 V extension cord.

Compute the voltage drop and percentage drop on a copper extension cord given AWG, one-way length, and current draw. Drops over 5% may stop tools from running properly.

Marcus Laurent By Marcus Laurent
Published Last reviewed 1 min read

Inputs

ft
A

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

V_drop = 2 · I · L · R_per_ft (AWG dependent). Drop % = V_drop / 120 × 100.

In depth

Compute the voltage drop and percentage drop on a copper extension cord given AWG, one-way length, and current draw. Drops over 5% may stop tools from running properly.