★ CONSTRUCTION · REFERENCE TABLE · WORKSHOP SAFETY
A 15 amp tool on a 50 ft cord needs 14 AWG. Thinner cords run hot and starve the tool; longer runs and higher amps need heavier gauge. Enter your tool's amps and cord length and the chart gives you the gauge.
Gauge is the thickness of the copper inside the cord, and AWG numbers run backwards: lower means thicker. This chart matches your tool's amps and your cord's length to the gauge that keeps the cord cool and the tool at full power.
The rule is simple and it runs through every cell: heavier gauge (a lower AWG number) for longer runs and higher amps. A thin, long cord resists the current, and that resistance shows up as heat in the cord and lost voltage at the tool — the tool runs slower, weaker, and hotter than it should. The table below reproduces the Electrical Safety Foundation International (ESFI) extension-cord guidance exactly: each cell is the range of tool amps that gauge covers at that length. Read it by finding the gauge whose range contains your tool's amps at your cord length; where two gauges cover the same band (12 AWG and 10 AWG both cover 16–20 A at 25–50 ft), the thinner gauge is the recommendation. If your length falls between two columns, use the next longer column. Source: Electrical Safety Foundation International (ESFI) extension cord gauge table. Always follow the markings on your cord and your tool manufacturer's instructions where they differ — manufacturer markings take precedence over this general table.
| Cord gauge | 25–50 ft | 100 ft | 150 ft |
|---|---|---|---|
| 16 AWG | 1–13 A | 1–10 A | Not listed |
| 14 AWG | 14–15 A | 11–13 A | 1–7 A |
| 12 AWG | 16–20 A | 14–15 A | 8–10 A |
| 10 AWG | 16–20 A | 16–20 A | 11–15 A |
How to read it. Find your tool's amps on its nameplate, find your cord length, and find the gauge whose range contains those amps. A 15 A circular saw on a 50 ft cord meets 14 AWG — the calculator's default, and the cell this page's lookup returns, because 14 AWG covers 14–15 A at 25–50 ft. An 8 A tool on a 100 ft cord needs 16 AWG (1–10 A at 100 ft), a 15 A tool on a 100 ft cord needs 12 AWG (14–15 A at 100 ft), and a 20 A tool on a 50 ft cord needs 12 AWG (16–20 A at 25–50 ft; 10 AWG also covers that band). If your tool and length have no cell — for example 18 A at 150 ft, where no gauge is listed for 16–20 A — this chart stops: use a shorter cord or check the manual and consider a dedicated circuit rather than a longer cord.
Line 1 — the tool. A 15 A tool needs a gauge whose ESFI range contains 15 A.
Line 2 — the length. A 50 ft run uses the 25–50 ft column (a 40 ft run lands in it too; a 75 ft run rounds up to the 100 ft column).
Line 3 — the cell. In the 25–50 ft column, 14 AWG covers 14–15 A, so the answer is 14 AWG.
Line 4 — the check. Never use a cord rated below the tool's amps: a 16 AWG cord on this job would be undersized, whatever its length.
At 100 ft a 15 A tool already needs 12 AWG, and at 150 ft it needs 10 AWG (11–15 A at 150 ft) — voltage drop is no longer a footnote but the problem: the tool sees noticeably less than 120 V, motors strain and overheat, and the cord itself runs warm along its whole length. Beyond 150 ft the ESFI table lists nothing, and that silence is the answer: the better move is a closer outlet, a shorter run, or a dedicated circuit, and the tool manual's maximum cord length, where it gives one, overrides this chart. Never daisy-chain two extension cords to reach further: every connection adds resistance and a failure point.
Gauge is only half the cord. Indoor cords (light jackets, often marked for indoor use) are not weatherproof and must never be used outside, where rain, sun, and abrasion break them down. Outdoor cords carry a heavier, weather-resistant jacket and are marked for outdoor use (look for a W marking) — they cost more for the same gauge, and that is the part you should not economize on. A cord used outdoors must also plug into a GFCI-protected outlet, and the connection between cord and tool should stay dry and off the ground.
| Output | Formula | What it means |
|---|---|---|
| ESFI range | Gauge range containing tool amps | 14 AWG covers 14–15 A at 25–50 ft at the defaults — the cell you read. |
| Length column | Cord length, rounded up | 25–50 ft at the defaults — the column you read down. |
| Recommended gauge | Gauge whose range contains tool amps | 14 AWG at the defaults — the cord to buy or reach for. |
| Undersized warning | Gauge thinner than the cell | A thinner cord runs hot and starves the tool — upsize, do not push through. |
This chart reproduces the ESFI table exactly: four gauges by three length columns, and it is deliberately conservative at the boundaries — a 60 ft run rounds up to the 100 ft column, and a tool-and-length combination with no listed cell (such as 18 A at 150 ft) is not answered with a guess. Real ampacity also depends on the cord's temperature rating, whether it is coiled (a coiled cord traps its own heat), ambient temperature, and whether the tool draws its rated amps continuously or in bursts — a coiled cord on a hot day needs more margin than this chart shows. The markings on your cord and your tool manufacturer's instructions take precedence over this general table, and local electrical codes govern fixed wiring, which this page does not cover. Error policy: empty, zero, or negative inputs, tools above 20 A, lengths above 150 ft, and combinations the ESFI table does not list are reported as errors rather than answered.
Bright Side Kit. "Extension Cord Gauge Chart: Pick the Right AWG Size." https://brightoolbox.com/extension-cord-gauge-chart/ Accessed October 24, 2026.14 AWG. In the ESFI table, 14 AWG covers 14–15 A at 25–50 ft. The same 15 A tool needs 12 AWG at 100 ft (14–15 A at 100 ft) and 10 AWG at 150 ft (11–15 A at 150 ft).
Yes, within the chart: a shorter run genuinely needs less copper, which is why the same 15 A tool needs 14 AWG at 25–50 ft but 12 AWG at 100 ft. What you must never do is use a cord rated below the tool's amps at any length, or a gauge whose ESFI range does not contain your tool's amps at your length.
Warmth means the cord is resisting the current — usually because it is undersized for the tool, too long for its gauge, coiled up (which traps heat), or damaged. Stop, uncoil it, let it cool, and check the chart: an undersized cord must be replaced with a heavier gauge, not kept in service.
No. Indoor cords lack the weather-resistant jacket outdoor cords carry, and rain, sun, and abrasion break them down. Outdoor cords are marked for outdoor use; use one, on a GFCI-protected outlet, with the connection kept dry.
Voltage drop becomes the main problem: the tool gets less than full voltage, runs weak and hot, and the cord warms along its length. A 15 A tool needs 12 AWG at 100 ft and 10 AWG at 150 ft, and beyond 150 ft the ESFI table lists nothing — prefer a closer outlet or dedicated circuit, and never daisy-chain two cords to reach further.
Thicker. AWG runs backwards: 10 AWG is much thicker copper than 16 AWG, carries more current, and costs more. When the chart says to go heavier, it means a lower AWG number.
12 AWG at 25–50 ft (16–20 A; 10 AWG also covers that band) and 10 AWG at 100 ft (16–20 A). At 150 ft no gauge is listed for 16–20 A, so a 20 A tool on a 150 ft cord is not covered by the table. A 20 A tool also needs a 20 A-rated cord end and circuit — the gauge alone does not make an undersized plug safe.