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Cord Tool

Extension Cord Size Calculator

// CHOOSE A PRACTICAL COPPER EXTENSION CORD GAUGE FROM AMPS, RUN LENGTH, SUPPLY VOLTAGE, AND VOLTAGE-DROP TARGET //

CORD_INPUTS

Uses a round-trip conductor path for single-phase portable loads.

Enter the real running current, not only the breaker size.

Distance from receptacle to load in feet.

Tight targets help motors, compressors, pumps, and sensitive electronics.

Allowed drop
3.60 V
Load basis
12.0 A
Length basis
75 ft
CORD_SIZE_RESULT
Recommended minimum
12 AWG

Passes 12.0 A and 3% drop target.

Estimated drop
2.38%

2.86 V on the selected cord size.

This recommendation is a practical planning minimum for a copper extension cord at the entered load and length.

16 AWG
Planning current screen: 13 A max
Drop
7.23 V
Drop %
6.02%
Status
No
14 AWG
Planning current screen: 15 A max
Drop
4.54 V
Drop %
3.79%
Status
No
12 AWG
Planning current screen: 20 A max
Drop
2.86 V
Drop %
2.38%
Status
Pass
10 AWG
Planning current screen: 30 A max
Drop
1.80 V
Drop %
1.50%
Status
Pass
8 AWG
Planning current screen: 40 A max
Drop
1.13 V
Drop %
0.94%
Status
Pass
HOW_THIS_TOOL_WORKS

The calculator checks common copper cord sizes from 16 AWG through 8 AWG.

Each option must pass both the entered current and the selected voltage-drop target.

Voltage drop uses round-trip conductor length, which is why a 100-foot cord is calculated as 200 feet of conductor path.

WHEN_TO_UPSIZE

Motors, compressors, pumps, and pressure washers usually benefit from a 2% to 3% drop target.

Portable heaters and other long-running loads should use real running current, not a rounded estimate.

If plugs feel warm or the tool starts sluggishly, shorten the run or move up another gauge.

IMPORTANT_LIMITS

This is a planning tool, not a substitute for the cord manufacturer rating or the equipment instructions.

Do not use extension cords as permanent wiring through walls, ceilings, floors, or concealed spaces.

Large generators, welders, and specialty flexible cable systems may need cord types and conductor sizes beyond this simplified range.

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