AWG to mm² Wire Gauge Converter
Free AWG to mm² wire gauge converter. Bidirectional conversion with NEC ampacity tables. Calculate wire diameter, resistance, and current capacity for copper and aluminum conductors.
NEC Ampacity Reference Table
| AWG | mm² | 60°C Cu | 75°C Cu | 90°C Cu | 60°C Al | 75°C Al | 90°C Al |
|---|
Based on NEC Table 310.16. Not more than three current-carrying conductors in raceway, cable, or earth (directly buried), based on ambient temperature of 30°C (86°F).
What is AWG (American Wire Gauge)?
AWG (American Wire Gauge), also known as Brown & Sharpe wire gauge, is a standardized wire gauge system used in North America since 1857. It defines the diameter and cross-sectional area of solid, round, non-ferrous electrical wire.
The AWG scale is logarithmic, meaning each step represents a constant ratio of diameters. The governing formula is:
dn = 0.005 inch × 92(36-n)/39
where n is the AWG number (negative for large gauges: 4/0 = -3, 3/0 = -2, 2/0 = -1, 1/0 = 0). A change of 3 AWG numbers roughly halves or doubles the cross-sectional area. A change of 6 AWG numbers roughly halves or doubles the diameter. A change of 10 AWG numbers corresponds to a factor of 10 in cross-sectional area.
NEC Ampacity Table (Table 310.16)
The National Electrical Code (NEC) Table 310.16 specifies the maximum allowable ampacity (current-carrying capacity) for copper and aluminum conductors at different temperature ratings. The table above provides these values at a glance.
- 60°C column: Used for conductors rated 60°C (e.g., TW, UF types) and for circuits under 100A per NEC 110.14(C)(1).
- 75°C column: The most common column for industrial applications. Used for THW, THWN, and most modern wire types rated 75°C or higher in equipment rated 75°C.
- 90°C column: Used for THHN, XHHW, and other high-temperature wires — but only for derating calculations per NEC 110.14(C). Terminations are still limited to the 60°C or 75°C column.
Common Use Cases
- Panel Wiring (Industrial Control): AWG 14–18 is typical for PLC I/O and control panel wiring. AWG 12 for power distribution within panels.
- Building Electrical: AWG 14 for 15A lighting circuits, AWG 12 for 20A receptacle circuits, AWG 10 for 30A circuits (dryers, water heaters).
- Automotive Wiring: AWG 16–22 for sensors and signal wiring, AWG 10–14 for high-current accessories. Automotive ampacity differs from NEC due to higher temperature ratings and shorter runs.
- Marine Wiring: Follows ABYC standards. Generally use the 105°C rated wire and derate per ABYC E-11 tables. Marine wiring typically uses tinned copper for corrosion resistance.
- Solar PV Systems: AWG 10–14 for module interconnections, larger for combiner box to inverter runs. Must account for continuous duty (125% factor per NEC 690).
Frequently Asked Questions
What is the difference between AWG and mm²?
AWG is a North American gauge system based on the wire's diameter (logarithmic scale). mm² (square millimeters) is the metric measurement of the actual cross-sectional area of the conductor. While AWG uses arbitrary gauge numbers, mm² directly states the conductor area. For example, AWG 12 = 3.309 mm². The table above provides conversions for all common sizes.
How do I choose the right wire gauge for my project?
Determine the expected load current (Amps), then select a wire gauge whose ampacity (from the NEC table) exceeds that current. Consider: (1) breaker rating must be less than or equal to wire ampacity, (2) voltage drop for long runs (use our Voltage Drop Calculator), (3) ambient temperature derating, (4) number of conductors in conduit, and (5) termination temperature ratings.
Why does wire gauge get smaller as the number gets bigger?
The AWG system was originally based on the number of drawing operations needed to produce the wire. AWG 0 (1/0) was the starting point, and each subsequent gauge number represented an additional drawing pass through progressively smaller dies. So AWG 40 went through 40 drawing operations, making it extremely thin. The numbers 00 (2/0), 000 (3/0), and 0000 (4/0) represent wires larger than the baseline that went through fewer drawing passes.
Can I use aluminum wire instead of copper?
Yes, but aluminum has higher resistance and lower ampacity than copper of the same gauge. For example, AWG 12 copper handles 25A at 75°C, but AWG 12 aluminum handles only 20A at 75°C. When using aluminum, you typically need to go up one or two AWG sizes for the same current capacity. Aluminum also requires proper anti-oxidation compound and connections rated for aluminum (CO/ALR or CU/AL).
What about stranded vs. solid wire?
The AWG system applies to both solid and stranded wire. For the same AWG, stranded wire has a slightly larger overall diameter due to air gaps between strands, but the cross-sectional area of copper is the same. Ampacity ratings in NEC Table 310.16 apply to both solid and stranded conductors of the same AWG size.