What wire gauge for 20 amps?
12 AWG copper NM-B is rated 20 A at 60°C.
Wire sizing starts with **load amps**. For resistive loads: **Amps = Watts ÷ Volts**.
**Continuous loads** (heaters, dryers running 3+ hours) use a **125% factor** before matching wire ampacity.
**Example — 1,920 W space heater at 120 V:**
1,920 ÷ 120 = **16 A**
16 × 1.25 = **20 A design**
Minimum copper NM-B (60°C): **12 AWG** (20 A)
**Ampacity reference (copper NM-B, 60°C):**
14 AWG = 15 A · 12 AWG = 20 A · 10 AWG = 30 A · 8 AWG = 40 A
Local code, conduit fill, ambient temperature, and installation method can require larger wire. This calculator is an estimate — verify with a licensed electrician.
Concise answers for common searches — definitions, steps, and comparisons.
12 AWG copper NM-B is rated 20 A at 60°C.
The calculator converts watts to amps (or accepts amps directly), applies a 125% continuous-load factor when enabled, and selects the smallest AWG from a 60°C copper NM-B ampacity table.
Formula
Design amps = Load amps × 1.25 (if continuous) → minimum AWG where ampacity ≥ design ampsUse watts + voltage for appliances, or enter amps directly if you know circuit current.
Enable continuous (125% sizing) for heaters, dryers, and equipment that runs 3+ hours.
Result shows smallest copper wire gauge whose ampacity meets the design load.
Use the Voltage Drop Calculator if the wire run exceeds ~50 ft.
Pair with the Breaker Size Calculator — breaker must not exceed wire ampacity.
Input
1,920 W · 120 V · continuousOutput
12 AWGInput
15 A · non-continuousOutput
14 AWGCommon real-world scenarios where this tool saves time.
1,920 W at 120 V → 16 A → 12 AWG with continuous sizing.
5,500 W at 240 V → ~23 A → 10 AWG with continuous factor.
15 A non-continuous load → 14 AWG minimum.
Step-by-step chains that connect related tools for common tasks.
| AWG | Ampacity | Typical breaker |
|---|---|---|
| 14 | 15 A | 15 A |
| 12 | 20 A | 20 A |
| 10 | 30 A | 30 A |
| 8 | 40 A | 40 A |
Local code, ambient temperature, and conduit fill may require larger wire.
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12 AWG copper NM-B is rated 20 A at 60°C — the standard pairing for a 20 A breaker on branch circuits.
No — 14 AWG is limited to 15 A ampacity. Undersized wire is a fire hazard.
Ampacity sets minimum gauge; long runs may need larger wire to limit voltage drop below 3–5%.
This is a DIY estimate using common ampacity tables. Permits and inspections require a licensed electrician.
14 AWG copper NM-B at 60°C is the standard minimum for a 15 A branch circuit with a 15 A breaker.
Load watts, amps, and voltage values are processed only in your browser — EverydayTools does not store circuit inputs.
Estimate only — not NEC certification, permit approval, or licensed electrical design. Verify with local code and inspection.
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Reviewed on 2026-03-01.
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