What Gauge Extension Cord for 15 Amps?
Plain-English answer
For a true 15A temporary load, a short run may start at 14 AWG, but 12 AWG is often the more comfortable real-world answer once the cord gets longer, the load starts hard, or the setup feels less predictable.
At 100 feet, a full 15A load often pushes the planning answer to 10 AWG if you want voltage drop under better control.
The key idea is that breaker size alone does not choose the cord. Current, length, load type, cord quality, and voltage drop all matter. Extension cords are temporary tools, not substitute house wiring.
If you want the quickest tailored answer, use the Extension Cord Size Calculator.
Quick starting point
A 15A cord question usually means you are already near the upper end of common household extension-cord use. That is why short, light-duty answers stop being reliable fast. A cord that looks acceptable for a short shop-vac run can become a poor choice at 50 or 100 feet, especially on 120V loads.
For homeowner planning, think in three buckets: short runs may still fit 14 AWG, medium runs often push toward 12 AWG, and long 100-foot runs often make 10 AWG the better starting point for a real 15A load.
Worked examples
Example 1: 15A tool on a 25 ft cord
Say a tool is drawing the full 15A on 120V and the cord is only 25 ft long. Using a common 14 AWG cord resistance of about 2.525 ohms per 1000 ft:
V drop = (2 x 25 x 15 x 2.525) / 1000 = 1.89V
That is about 1.58% drop on 120V, which is why 14 AWG can still work as a short-run planning minimum. Even here, many homeowners still choose 12 AWG for a little more margin on hard-starting tools.
Example 2: Same 15A load on a 100 ft cord
Now keep the same load and stretch the cord to 100 ft.
14 AWG drop = (2 x 100 x 15 x 2.525) / 1000 = 7.58V
That is about 6.31% drop, which is already a weak planning result. Move up to 12 AWG and the drop is still about 3.97%. Move up again to 10 AWG and the drop lands around 2.50%. That is why a full 15A load at 100 ft often points to 10 AWG.
Common 15A cord cases at a glance
| Temporary setup | Typical load | Distance effect | Practical starting point |
|---|---|---|---|
| Short 25 ft full-load tool run | Near 15A | Usually modest | 14 AWG minimum, 12 AWG often nicer |
| 50 ft full-load temporary run | Near 15A | More noticeable | 12 AWG often the better answer |
| 100 ft full-load 120V run | Near 15A | Strong voltage-drop effect | 10 AWG often the better starting point |
| Long-running heater-like load | High, steady draw | Heat and drop both matter | Usually change approach instead of relying on a cord |
These are planning baselines only. Cord build quality, terminations, jacket rating, and the actual equipment instructions still matter.
Use the calculator before you buy the cord
The Extension Cord Size Calculator is the fastest way to test your actual amps, cord length, and drop target. If you want to inspect the voltage-loss side more directly, run the same setup through the Voltage Drop Calculator next.
What changes the answer?
- Actual load current: a 12A tool and a true 15A load do not deserve the same casual cord answer.
- Cord length: 25 ft, 50 ft, and 100 ft can change the recommendation by one or two sizes.
- Load type: motors and compressors can be less forgiving than simple lighting or electronics.
- Cord construction: cords with the same printed gauge do not all behave equally if one has weaker ends, poorer flexibility, or questionable labeling.
- 120V vs 240V: 120V loads usually feel voltage drop sooner.
When not to use an extension cord
Change approach if the cord is being used as everyday wiring for a room, shed, freezer, or heater, if it will stay in place for days at a time, or if the cord must stay coiled while carrying a high load. That is no longer a normal temporary-use setup.
Stop and rethink the plan if the equipment manual says to plug directly into a wall outlet, if the cord or plug gets warm, or if the setup already trips breakers. In those cases, a different outlet, a shorter run, or a proper branch circuit is usually the safer answer.
Related extension-cord planning tools
FAQ
Is 14 AWG enough for 15 amps?
Sometimes on a short temporary run, yes. But it is not the best blanket answer for every 15A setup. Length, motor startup, and voltage drop often push the better planning answer to 12 AWG or 10 AWG.
What gauge cord is better for 15 amps at 100 feet?
For a real 15A 120V load, 100 feet often pushes the practical answer toward 10 AWG. That is where voltage drop starts changing the decision in a big way.
Does a 15A breaker mean a 15A cord is automatically fine?
No. The breaker protects the house wiring. The cord still has to be suitable for the current, length, and equipment you are actually using.
Can I use a 15A extension cord for a space heater?
Usually the better answer is no. Space heaters are high, steady loads and many manufacturers want them plugged directly into a wall outlet. See Can You Run a Space Heater on an Extension Cord?.
Disclaimer: Results are informational estimates for learning and planning only. Always follow the applicable electrical code and consult a qualified licensed electrician for safety-critical work.