Wire Sizing Calculator
Calculate the correct wire gauge for any electrical circuit using NEC ampacity tables. Supports copper and aluminum conductors with all temperature ratings.
Use Calculator in AppWhat is Wire Sizing?
Wire sizing is the process of selecting the correct conductor gauge (AWG) for an electrical circuit based on the load current, temperature rating, and installation conditions. Proper wire sizing is essential for safety and NEC code compliance.
Undersized wire can overheat, causing insulation damage, fire hazards, and equipment failure. Oversized wire wastes money and can make installation difficult. The NEC provides ampacity tables to help electricians select the right conductor size.
NEC Table 310.16 - Copper Conductor Ampacity
Allowable ampacities for insulated copper conductors rated 0 through 2000 volts, not more than 3 current-carrying conductors in raceway or cable, ambient temperature of 30°C (86°F).
| Wire Size (AWG) | 60°C (TW, UF) | 75°C (THW, THWN) | 90°C (THHN, XHHW) |
|---|---|---|---|
| 14 AWG | 15A | 15A | 15A* |
| 12 AWG | 20A | 20A | 20A* |
| 10 AWG | 30A | 35A | 40A |
| 8 AWG | 40A | 50A | 55A |
| 6 AWG | 55A | 65A | 75A |
| 4 AWG | 70A | 85A | 95A |
| 3 AWG | 85A | 100A | 115A |
| 2 AWG | 95A | 115A | 130A |
| 1 AWG | 110A | 130A | 145A |
| 1/0 AWG | 125A | 150A | 170A |
| 2/0 AWG | 145A | 175A | 195A |
*NEC 240.4(D) limits 14 AWG to 15A, 12 AWG to 20A, and 10 AWG to 30A regardless of ampacity.
Ambient Temperature Correction Factors
When the ambient temperature exceeds 30°C (86°F), ampacity must be reduced using correction factors from NEC Table 310.15(B)(1).
| Ambient Temp (°C) | 60°C Wire | 75°C Wire | 90°C Wire |
|---|---|---|---|
| 31-35°C | 0.91 | 0.94 | 0.96 |
| 36-40°C | 0.82 | 0.88 | 0.91 |
| 41-45°C | 0.71 | 0.82 | 0.87 |
| 46-50°C | 0.58 | 0.75 | 0.82 |
Conduit Fill Adjustment Factors
When more than 3 current-carrying conductors are bundled together, ampacity must be reduced per NEC 310.15(C)(1).
Wire Sizing Example
Problem:
Size the conductors for a 60A circuit using THHN copper wire in a conduit with 6 current-carrying conductors at an ambient temperature of 40°C.
Solution:
Required ampacity = 60A ÷ (0.91 × 0.80) = 60 ÷ 0.728 = 82.4A
From Table 310.16 (90°C column): 4 AWG = 95A
Use 4 AWG THHN copper conductors
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