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How Many Amps Can a 16-Gauge Extension Cord Handle?

Plan on about 10 amps for a typical 16-gauge outdoor extension cord, which is roughly 1,200 watts at 120 volts. The National Electrical Code (NEC) allows a bit more on paper, but the number stamped on the cord's jacket is the one that actually governs, and on the common longer cords that number is usually 10 amps. Two things trim it further: a load that runs for hours should sit at about 80 percent of the rating, so closer to 8 amps, and a long cord can lose enough voltage over the distance to matter before it ever reaches its amp limit. If the number you need is higher than that, the answer is a heavier cord, not a longer 16-gauge one.

Amps are only half the story on a long run. Enter your cord's length and the load it carries in the Extension Cord Voltage Drop Calculator to see whether the voltage still holds at the far end, because that is what usually maxes out a thin cord first.

What the rating actually is

A 16-gauge cord describes the thickness of the copper inside: the bigger the gauge number, the thinner the wire, and the less current it can carry before it heats up. For flexible cords, the code puts the allowable current in NEC Table 400.5(A)(1). A 16 AWG cord with two current-carrying conductors, which is a standard hot-neutral-ground extension cord, is listed at 13 amps; where three conductors carry current the same size drops to 10 amps.

In the store, though, the printed rating on a 16-gauge cord is very often 10 amps, sometimes shown as a wattage like 1,250 watts, because the listing agency accounts for the cord's length and how it is used. That printed number is the one to follow. When your cord says 10 amps, treat it as a 10-amp cord even though the table would allow 13.

A plain worked example

Say the cord is stamped 10 amps and you want to run a stretch of decorations off it. Watts divide by volts to give amps, so first turn each item's wattage into amps at 120 volts:

Light strings, 480 W total ÷ 120 V = 4.0 A

Two inflatable blowers, 480 W total ÷ 120 V = 4.0 A

Running total = 4.0 + 4.0 = 8.0 A

Eight amps on a 10-amp cord is right at the 80 percent line the code uses for anything left running for hours (10 A × 0.80 = 8 A), so that display is a sensible full load for the cord and nothing more should go on it. Now add a fog machine:

Previous total = 8.0 A

Fog machine, 600 W ÷ 120 V = 5.0 A

New total = 8.0 + 5.0 = 13.0 A

Thirteen amps sits right at the code's 13-amp table ceiling for this size and well past the cord's own 10-amp stamp. On a 16-gauge cord that load heats the copper, softens the jacket, and can start a fire long before the breaker at the panel ever notices, because the breaker protects the house wiring, not your thin cord. The fix is to split the load across two circuits or step up to a 12-gauge cord, which the code lists at up to 25 amps for the same two-conductor case.

Why length quietly lowers the answer

A cord's amp rating assumes a reasonable length. Stretch a thin cord out across the yard and the resistance of all that copper drops the voltage before it reaches the load, so lights dim and motors run hot even though the current is still under the amp limit. Using the resistance the NEC lists for 16 AWG copper in Chapter 9, Table 8, a 100-foot 16-gauge cord carrying that same 8 amps loses:

Drop = 2 × amps × resistance × (length ÷ 1000)

Drop = 2 × 8 A × 4.89 Ω × (100 ÷ 1000)

Drop ≈ 7.8 V, about 6.5% of 120 V

That 6.5 percent is past the 5 percent most equipment is happy with, so at 100 feet the 16-gauge cord is effectively full on voltage drop while it still has amps to spare. Shorten the run, split the load, or move up to a heavier gauge. The Extension Cord Voltage Drop Calculator runs this for your exact cord and load, and the Wire Ampacity Calculator shows the same current-versus-conductor-size idea for permanent building wire.

The short version

  • Plan on 10 amps for a common 16-gauge cord, about 1,200 watts at 120 volts. Follow the number printed on the jacket.
  • Keep an all-evening load near 8 amps, the 80 percent line for anything running for hours.
  • Long runs max out on voltage, not amps. Around 100 feet a 16-gauge cord is already losing more than 5 percent.
  • Need more? Go heavier, not longer. A 12-gauge cord carries far more current for the same run.

NEC reference

NEC 2020. Flexible-cord ampacity is Table 400.5(A)(1): 16 AWG is listed at 13 amps with two current-carrying conductors and 10 amps with three, and 12 AWG at 25 and 20 amps for the same two cases. The 80 percent figure for a load running three hours or more mirrors the continuous-load rule in 210.19(A) and 210.20(A); a continuous load is defined in Article 100. The 4.89 ohms per 1,000 feet used for the 16 AWG voltage-drop example is the direct-current resistance for solid uncoated copper in Chapter 9, Table 8. Watts equal volts times amps is the power relationship, not a code value. Cord markings reflect the product's UL listing, which can be more restrictive than the table, and the printed rating governs.

Results are for reference only. Verify against the applicable adopted edition of the NEC and consult a licensed electrician for code compliance.

Get the full guide

NEC Code Quickstart

This guide covers one calculation. NEC Code Quickstart walks all twelve exam calculations start to finish, each with a worked example and the exact code reference: ampacity and derating, breaker sizing, voltage drop, box and conduit fill, grounding, dwelling load, range and dryer demand, motor circuits, and transformer current. Written for the 2023 NEC with notes for the 2026 edition.

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