Home energy · electrical safety
Extension cord gauge, by amps and length.
Enter the device load and the cord length. The tool looks up the minimum wire gauge in a published table and warns when the load falls outside it.
Short answer
Minimum gauge depends on both amps and length. A 15 A load on a 100 ft cord needs 12 AWG, while the same load on a 50 ft cord needs 14 AWG. A smaller AWG number is a thicker wire.
Load and cord
Result
Worked example
A saw rated 15 A on a 100 ft cord: the 100 ft row lists 14 to 15 A at 12 gauge, so the minimum is 12 AWG. A 10 A load on a 150 ft cord falls in the 8 to 10 A row of the 150 ft table, which is 12 AWG. A 1,200 W tool at 120 V is 10 A; on a 50 ft cord that is 16 AWG in the table. A cord length between rows uses the next longer row.
Formula, assumptions and sources
The table is the University of Texas at Austin EHS extension cord factsheet, which says it is adapted from the OSHA eTool on flexible cords and credits the cord-size chart to The Home Depot. Rows: 25 ft and 50 ft: up to 13 A 16 gauge, 14 to 15 A 14 gauge, 16 to 20 A 12 gauge (heavy duty) or 10 gauge (extra heavy duty). 100 ft: up to 10 A 16, 11 to 13 A 14, 14 to 15 A 12, 16 to 20 A 10. 150 ft: up to 7 A 14, 8 to 10 A 12, 11 to 15 A 10. Amps are rounded up to the next whole number and length up to the next table row. The factsheet also says cords must be three-wire, and the OSHA construction standard requires hard or extra-hard usage ratings. Loads above the table or lengths over 150 ft are outside it; the tool says so rather than guess. Cord insulation, outdoor rating and damage matter as much as gauge.
Source: University of Texas at Austin EHS, Factsheet: Extension Cords (table credited to The Home Depot) (opened 2026-10-08)
Source: U.S. Consumer Product Safety Commission, Reducing Fire Hazards for Portable Electric Heaters (opened 2026-10-08)
Safety and limits
This is a planning aid, not professional advice. Electrical and HVAC work can cause fire, shock and carbon monoxide hazards; have a licensed professional size, install and inspect equipment.
FAQ
What gauge extension cord do I need for 15 amps?
On a 25 or 50 ft cord, 14 gauge; on 100 ft, 12 gauge; on 150 ft, 10 gauge, according to the table used here.
Is a lower gauge number thicker?
Yes. 10 AWG is thicker than 16 AWG and carries more current over a longer distance.
Can I run a space heater on an extension cord?
The CPSC heater safety sheet says never to power the heater with an extension cord or power strip. This tool does not make that safe.