AWG Wire Size Chart & Calculator by Amperage
The AWG (American Wire Gauge) system is an inverse logarithmic scale: the higher the number, the thinner the wire. Every 6 gauge steps, the cross-sectional area halves. AWG 14 (2.08 mm²) is the minimum for 15 A household branch circuits per the NEC (National Electrical Code); AWG 12 (3.31 mm²) is required for 20 A kitchen circuits. Undersizing wire causes resistive heating, insulation damage, and fire hazards. This calculator applies NEC 310.15 ampacity tables and the standard 80%/125% derating rule for continuous loads.
AWG wire size by ampacity (75°C copper, NEC): **AWG 14 = 15 A**, AWG 12 = 20 A, AWG 10 = 30 A, AWG 8 = 40 A, AWG 6 = 55 A, AWG 4 = 70 A, AWG 2 = 95 A. For continuous loads (≥3 hours), multiply the load by 1.25 before selecting the gauge — e.g., 16 A continuous → AWG 12 (20 A rated). Higher AWG number = thinner wire.
When to use this calculator
- Sizing residential branch circuits: AWG 14 (15 A) or AWG 12 (20 A) per NEC 210.52.
- Selecting wire gauge for a 240 V electric dryer drawing 30 A — requires AWG 10 minimum.
- Solar panel wiring: correct gauge for a 40 A DC string combiner run to avoid >2% voltage drop.
- Automotive wiring: choosing AWG for a 60 A alternator output cable with temperature derating.
- Industrial motor feeder sizing: applying NEC 430.22 for a 20 HP, 230 V single-phase motor.
Worked Example — 15 A Bedroom Circuit
- Input: 15 A, General installation (75°C)
- Lookup: AWG 14 is rated 15 A at 75°C (NEC Table 310.15(B)(16))
- Cross-section: 2.08 mm² — diameter: 1.63 mm
- If load is continuous (≥3 h): 15 A × 1.25 = 18.75 A → upsize to AWG 12 (20 A)
How it works
3 min readAWG Wire Size by Amperage — Quick Reference Table
| AWG | Diameter (mm) | Area (mm²) | Max 60°C | Max 75°C | Max 90°C | Typical Use |
|---|---|---|---|---|---|---|
| 18 | 1.02 | 0.82 | 7 A | 10 A | 14 A | Low-voltage lighting |
| 16 | 1.29 | 1.31 | 10 A | 13 A | 18 A | Extension cords |
| 14 | 1.63 | 2.08 | 15 A | 20 A | 25 A | 15 A branch circuits |
| 12 | 2.05 | 3.31 | 20 A | 25 A | 30 A | 20 A kitchen circuits |
| 10 | 2.59 | 5.26 | 30 A | 35 A | 40 A | Dryers, A/C units |
| 8 | 3.26 | 8.37 | 40 A | 50 A | 55 A | Ranges, EV chargers |
| 6 | 4.11 | 13.30 | 55 A | 65 A | 75 A | 60 A subpanels |
| 4 | 5.19 | 21.15 | 70 A | 85 A | 95 A | Large HVAC feeders |
| 2 | 6.54 | 33.62 | 95 A | 115 A | 130 A | 100 A service entry |
| 1/0 | 8.25 | 53.48 | 125 A | 150 A | 170 A | 150 A service entry |
| 2/0 | 9.27 | 67.43 | 145 A | 175 A | 195 A | 200 A service panels |
Single copper conductor, per NEC Table 310.15(B)(16).
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How It Is Calculated
The AWG scale is defined by two anchor points: AWG 0000 (4/0) = 0.46 inches diameter and AWG 36 = 0.005 inches diameter, with 39 steps in between. Every 6 gauge steps, the cross-sectional area halves (or doubles going down).
Core Formula — AWG to Physical Dimensions
Diameter (inches) = 0.005 × 92^((36 − AWG) / 39)
Diameter (mm) = 25.4 × Diameter (inches)
Area (mm²) = π/4 × Diameter(mm)²
OR = 0.012668 × 92^((36 − AWG) / 19.5)Ampacity Derating for Continuous Loads (NEC 210.19 / 310.15)
For continuous loads (≥3 hours): Required Ampacity = Load (A) × 1.25Example: A 15 A continuous load requires a conductor rated for at least 18.75 A, so AWG 12 (20 A rated) is selected, not AWG 14 (15 A rated).
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Common Sizing Scenarios
15 A Household Circuit
Non-continuous 15 A at 120 V: AWG 14 (2.08 mm², 1.63 mm diameter). Protected by a 15 A breaker.
20 A Kitchen Circuit
NEC 210.11(C)(1) mandates 20 A small-appliance circuits: AWG 12 (3.31 mm²). Protected by a 20 A breaker.
30 A Electric Dryer (240 V)
Running current 24 A × 1.25 (continuous) = 30 A. AWG 10 (5.26 mm²) at 75°C column satisfies this. Paired with a 30 A double-pole breaker.
40 A Solar Combiner (DC, 50 ft)
String current 32 A. For <2% voltage drop at 48 V over 100 ft round trip: AWG 8 (8.37 mm²) handles both ampacity and drop.
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Common Sizing Errors
1. Ignoring the continuous load rule (×1.25): A 16 A continuous load needs AWG 12, not AWG 14.
2. Mixing temperature ratings: Using the 90°C column when terminals are rated 60°C or 75°C — NEC 110.14(C) requires the lowest rating in the circuit.
3. Forgetting conduit fill derating: 4–6 conductors in conduit = 80%; 7–9 = 70%; 10–20 = 50%.
4. Confusing AWG with mm² (IEC): AWG 14 = 2.08 mm², not 1.5 mm². They are not interchangeable.
5. Ignoring voltage drop on long runs: Ampacity tables prevent overheating, not voltage sag. Calculate ΔV = 2 × L × I × R for runs over 100 ft.
Frequently asked questions
What does AWG stand for, and why does a larger number mean a thinner wire?
AWG stands for American Wire Gauge, a standardized system dating to 1857. The numbering reflects the number of drawing dies needed: more draws = thinner wire = higher number. AWG 4/0 (thickest common size) = 11.68 mm diameter; AWG 36 = 0.127 mm. Every 6 AWG steps, the cross-sectional area halves.
What AWG wire do I need for 15 amps?
For a standard 15 A non-continuous circuit (e.g., a bedroom outlet), you need AWG 14 (2.08 mm², diameter 1.63 mm), protected by a 15 A breaker. If the load runs continuously for 3+ hours, multiply by 1.25 — 15 A × 1.25 = 18.75 A — and you'd need AWG 12 (20 A rated).
What AWG wire do I need for 20 amps?
AWG 12 (3.31 mm², diameter 2.05 mm) is required for 20 A circuits. AWG 14 is explicitly prohibited on 20 A breaker circuits. NEC 210.11(C)(1) mandates AWG 12 for kitchen small-appliance branch circuits.
How does the NEC 80% (125%) rule affect wire sizing for continuous loads?
Per NEC 210.19(A)(1), any load operating for 3+ hours must be calculated at 125% of actual current. Equivalently, a wire may only carry 80% of its rated ampacity for continuous loads. Example: a 16 A continuous load requires a 20 A-rated conductor — AWG 12, not AWG 14.
What is the difference between AWG 14 and 1.5 mm² wire? Can I substitute them?
No — they are NOT interchangeable. AWG 14 = 2.08 mm², which is larger than the European IEC 1.5 mm² (diameter 1.38 mm). The closest metric equivalent to AWG 14 is 2.5 mm². Substituting 1.5 mm² for AWG 14 in a 15 A circuit creates a fire hazard and violates NEC.
Does aluminum wire need a different AWG than copper?
Yes. Aluminum has ~61% the conductivity of copper, so it must be sized about 2 AWG numbers larger. AWG 12 copper = 20 A (75°C); AWG 12 aluminum = only 15 A. For a 20 A aluminum circuit, use AWG 10. Aluminum also requires anti-oxidant compound and CO/ALR-rated devices per NEC 310.106(B).
How do I calculate voltage drop for a long wire run?
ΔV = 2 × L × I × R_per_ft, where L is one-way run length and R_per_ft is conductor resistance (AWG 12 copper = 0.001588 Ω/ft; AWG 10 = 0.000999 Ω/ft). For a 100 ft run at 15 A on AWG 12: ΔV = 2 × 100 × 15 × 0.001588 = 4.76 V (~4% of 120 V). To stay under 3%, upsize to AWG 10.
Can I use the same AWG wire for DC circuits (solar, EV) as for AC circuits?
The physical wire is identical, but code requirements differ. NEC Article 690 (Solar PV) and Article 625 (EV charging) apply to DC. DC arcing does not self-extinguish at zero-crossing like AC, so OCPD ratings and insulation voltage ratings must be verified separately. AWG 10 rated for 30 A AC can be used on a 30 A DC solar string, but verify breaker and conduit requirements.