Ampacity
Flexible cord ratings with two current-carrying conductors (column B): 16 AWG 13 A, 14 AWG 18 A, 12 AWG 25 A, 10 AWG 30 A. The plug and receptacle usually limit a cord set to 15 A anyway.
Extension cord gauge chart by amps & length
Extension cord gauge chart: a cord must carry the current and keep the voltage up. 16 AWG is rated 13 A, 14 AWG 18 A, 12 AWG 25 A (Table 400.5(A)(1)). A 13 A saw needs 16 AWG at 50 ft and 12 AWG at 100 ft to stay under 5 % drop at 120 V.
04 · Extension cord gauge
13 A tool, 50 ft cord · 120 V, under 5 % drop
USE:
16 AWG EXTENSION CORD (16/3) · 13 A CORD RATING · 50 FT MAX
Cord gauge
16 AWG
3-conductor
Cord rating
13 A
Table 400.5(A)(1)
Length
50 ft
A 13 A load 50 ft from the outlet needs at least 16 AWG cord to stay under 5 % drop at 120 V and within the cord’s 13 A rating.
- Cord rating 13 A ≥ 13 A400.5(A)(1)
Cord
- Gauge
- 16 AWG
- Drop at this size
- 4.44 %stranded copper at 20 °C
Extension cord tables 25 rows
Sort any column, print a shop sheet, download CSV. Click a row to load it in the calculator.
| Actions | ||||||
|---|---|---|---|---|---|---|
| 600 | 16 AWG | 16 AWG | 16 AWG | 14 AWG | ||
| 960 | 16 AWG | 16 AWG | 14 AWG | 12 AWG | ||
| 1200 | 16 AWG | 16 AWG | 14 AWG | 12 AWG | ||
| 1440 | 16 AWG | 16 AWG | 12 AWG | 12 AWG | ||
| 1560 | 16 AWG | 16 AWG | 12 AWG | 10 AWG | ||
| 1800 | 14 AWG | 14 AWG | 12 AWG | 10 AWG | ||
| 1920 | 14 AWG | 14 AWG | 12 AWG | 10 AWG | ||
| 2400 | 12 AWG | 12 AWG | 10 AWG | 8 AWG |
Cord ratings (column B, two current-carrying conductors): 16 AWG 13 A, 14 AWG 18 A, 12 AWG 25 A, 10 AWG 30 A. Plugs limit most cord sets to 15 A.
| Actions | ||||||
|---|---|---|---|---|---|---|
| 600 | 16 AWG | 16 AWG | 14 AWG | 12 AWG | ||
| 960 | 16 AWG | 16 AWG | 12 AWG | 10 AWG | ||
| 1200 | 16 AWG | 14 AWG | 12 AWG | 10 AWG | ||
| 1440 | 16 AWG | 14 AWG | 10 AWG | 8 AWG | ||
| 1560 | 16 AWG | 14 AWG | 10 AWG | 8 AWG | ||
| 1800 | 14 AWG | 12 AWG | 10 AWG | 8 AWG | ||
| 1920 | 14 AWG | 12 AWG | 10 AWG | 8 AWG | ||
| 2400 | 12 AWG | 12 AWG | 8 AWG | 6 AWG |
Cord ratings (column B, two current-carrying conductors): 16 AWG 13 A, 14 AWG 18 A, 12 AWG 25 A, 10 AWG 30 A. Plugs limit most cord sets to 15 A.
| 18 AWG | 7 A | 10 A | 7.95 |
|---|---|---|---|
| 16 AWG | 10 A | 13 A | 4.99 |
| 14 AWG | 15 A | 18 A | 3.14 |
| 12 AWG | 20 A | 25 A | 1.98 |
| 10 AWG | 25 A | 30 A | 1.24 |
| 8 AWG | 35 A | 40 A | 0.778 |
| 6 AWG | 45 A | 55 A | 0.491 |
| 4 AWG | 60 A | 70 A | 0.308 |
| 2 AWG | 80 A | 95 A | 0.194 |
Correct for ambient temperatures other than 30 °C with Table 310.15(B)(1); more than three current-carrying conductors in one cord use 400.5(A)(2).
05 / Field guide
Two limits,
one cord.
An extension cord has to carry the current without overheating and deliver enough voltage that the tool keeps its speed. NEC Table 400.5(A)(1) gives the first limit; resistance and length give the second, and on long cords it is the one that decides.
Length
The chart keeps the drop under 5 % at 120 V with stranded copper at room temperature. A 13 A saw takes 16 AWG at 25 ft, 16 AWG at 50 ft, 12 AWG at 100 ft and 10 AWG at 150 ft.
V drop = 2 × L × I × R 5 % of 120 V = 6 V
Use and abuse
Uncoil a cord before running a heater or compressor on it; a coiled cord cannot shed heat. Cords are temporary wiring (400.12): they are not a substitute for a circuit.
Reading the jacket
The letters on a cord tell you where it can go. S is service grade, J junior (300 V), T thermoplastic, O an oil-resistant jacket (OO adds oil-resistant insulation), W weather-rated for outdoor use. SJTW is a common outdoor cord; SJOOW is a tougher rubber cord for job sites. The numbers give the gauge and conductor count: 12/3 is three 12 AWG conductors, including the ground.
Outdoors and in wet places
Outdoors, use a cord whose jacket letters end in W and plug it into a GFCI-protected receptacle; dwelling outdoor receptacles must have GFCI protection (210.8(A)(3)). Keep connections off wet ground or in a listed cover, and never run a cord through a doorway, window or under a rug, where damage goes unseen and the cord cannot shed heat. Replace a cord with a cut jacket rather than taping it.
Generators and RVs
A 30 A, 120/240 V generator inlet (NEMA L14-30) takes a four-conductor cord: two hots, a neutral and a ground. Only two conductors carry current at a time on a balanced load, so 10 AWG cord, rated 30 A in column B, is the usual choice. A 30 A RV cord (TT-30) is 10/3; a 50 A RV cord is 6/3 plus 8 AWG, sold as a finished cord set.
Questions
Answered plainly.
01What gauge extension cord for a 15 amp tool?
+−
14 AWG up to 25 ft, 14 AWG to 50 ft and 12 AWG to 100 ft.
02Is a 16 gauge extension cord safe?
+−
For lamps, chargers and small tools up to 13 A on short runs, yes. Not for heaters, compressors or saws on long runs.
03What size cord for a space heater?
+−
A 1500 W heater draws 12.5 A; most makers say not to use a cord at all. If you must, use a heavy 12 or 14 AWG cord, short and uncoiled.
04What does 12/3 mean on a cord?
+−
12 AWG conductors, three of them (hot, neutral and ground). Only two carry current, so the cord uses column B of Table 400.5(A)(1).
05Why does my saw bog down on a long cord?
+−
Voltage drop. Motors draw more current when the voltage falls, which makes the drop worse; use a heavier gauge or a shorter cord.
06What does SJTW mean on an extension cord?
+−
Service grade, junior (300 V), thermoplastic jacket, weather-rated. It is suitable for outdoor use; for job sites a rubber SJOOW cord lasts longer.
07What cord for a 30 amp generator?
+−
A 10/4 cord for a 120/240 V L14-30 inlet, or 10/3 for a 120 V TT-30 RV outlet; 10 AWG cord is rated 30 A with two current-carrying conductors.