Extension Cord Size Chart: Gauge by Length & Amps 2026

How extension cord size is worked out

An extension cord is sized by the smallest gauge that fits both numbers at once: the cord must carry the tool’s amps, and it must carry them over the whole length. The table lists five standard gauges, thinnest first: 18 AWG carries 10 A over 25 ft, 16 AWG carries 13 A over 50 ft, 14 AWG carries 15 A over 100 ft, 12 AWG carries 20 A over 150 ft, and 10 AWG carries 30 A over 200 ft. The lookup walks the table from the thinnest gauge up and takes the first gauge whose max amps are at least the tool’s amps and whose max length is at least the cord’s length. If no gauge fits both, no standard cord does the job.

At the defaults — 50 ft, 12 A — 18 AWG fails on both counts: it carries only 10 A and reaches only 25 ft. 16 AWG carries 13 A, which is at least 12 A, and reaches 50 ft, which is at least 50 ft — so the answer is 16 AWG, rated for general household use.

The table is a sizing guide for ordinary extension cords, not a wire-stripping chart and not a voltage-drop chart: it does not list how much insulation to strip or how many volts a cord loses, and it is guidance, not NEC code — check the tool manual for the gauge the maker calls for.

The worked example, line by line

Setup: 50 ft, 12 A, reverse gauge 14 AWG.

Line 1 — the amps test. The tool draws 12 A. 18 AWG carries 10 A, which is less than 12 A, so 18 AWG fails the amps test.

Line 2 — the length test. The cord is 50 ft long. 18 AWG reaches 25 ft, which is less than 50 ft, so 18 AWG fails the length test too.

Line 3 — the next gauge. 16 AWG carries 13 A, which is at least 12 A, and reaches 50 ft, which is at least 50 ft — so the answer is 16 AWG, rated for general household use.

Line 4 — the reverse. A 14 AWG cord handles up to 100 ft at 15 A, and a 12 AWG cord handles up to 150 ft at 20 A.

Every branch, checked

25 ft / 8 A: 18 AWG carries 10 A, which is at least 8 A, and reaches 25 ft, which is at least 25 ft — so the answer is 18 AWG, light-duty indoor only. A short cord for a light tool is the one place the thinnest gauge is right.

100 ft / 13 A: 18 AWG fails both tests and 16 AWG reaches only 50 ft, so the answer is 14 AWG, which carries 15 A over 100 ft. A long run needs thicker wire even for a modest tool.

150 ft / 18 A: 14 AWG carries only 15 A, so the answer is 12 AWG, which carries 20 A over 150 ft. A heavy tool at a long distance needs the thicker cord.

25 ft / 15 A: 18 AWG carries only 10 A and 16 AWG only 13 A, so the answer is 14 AWG, which carries 15 A over 100 ft. A hungry tool needs thicker wire even on a short cord.

200 ft / 20 A: only 10 AWG reaches 200 ft, and it carries 30 A, so the answer is 10 AWG, for large equipment. This is the thickest standard cord in the table.

250 ft / 10 A: no gauge in the table reaches 250 ft — the longest standard cord is 200 ft — so the answer is no standard cord: use a shorter cord or a dedicated circuit. A cord that long is not a cord job at all.

Reverse — the gauges: 14 AWG handles up to 100 ft at 15 A, and 12 AWG handles up to 150 ft at 20 A. If you already own the cord, the reverse tells you how far it reaches and how much tool it can feed.

What the defaults assume

The model assumes the cord is an ordinary outdoor-rated extension cord in good condition, the tool draws its rated amps the whole time it runs, and the cord is fully uncoiled while it is used. It assumes one tool on one cord: two tools on one cord add their amps together, and the lookup must use the total. It leaves out the voltage drop in volts and the temperature of the cord — this is a sizing guide, not a voltage-drop chart, and it is guidance, not NEC code. Rounding convention: lengths and amps are whole numbers, gauges are standard AWG sizes, and all figures are computed from the table, not rounded.

Output · formula · meaning

Who uses this

• The homeowner running a saw to the back fence: they learn a 50 ft cord at 12 A needs 16 AWG — so they know the thin indoor cord in the garage is not the one to use, and they know 16 AWG is the thinnest cord that is still safe.
• The renovator on a 100 ft run: they learn 100 ft at 13 A needs 14 AWG — so they know the 50 ft cord they own is too short and too thin, and they buy the 14 AWG cord before the tool starves halfway through the cut.
• The gardener with a 150 ft run to the shed: they learn 150 ft at 18 A needs 12 AWG — so they know a heavy tool at a long distance needs the thicker cord, and they do not burn out the tool on a thin one.
• The buyer who already owns a 14 AWG cord: they learn 14 AWG handles up to 100 ft at 15 A — so they know the cord they own reaches the far corner and feeds the saw, and they do not buy a cord they do not need.

Accuracy & limitations

The math is exact for the table: the lookup takes the first gauge whose max amps are at least the tool’s amps and whose max length is at least the cord’s length, walking from the thinnest gauge up. What the model cannot do is read your tool’s plate for you: check the amps on the tool or in the manual, and use the rated amps, not the amps on the box. It is guidance, not NEC code — check the tool manual for the gauge the maker calls for, and never use a cord that is damaged, coiled tight while it runs, or rated for indoor use outdoors. 18 AWG is light-duty indoor only. For the wire inside the walls, see AWG wire ampacity chart; for the gauge of a fixed run, see wire gauge chart.