Wire Gauge Calculator
Look up AWG wire specs or find the minimum gauge for your current requirements.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Wire Gauge Calculator
This tool works in two modes: look up the specifications for a known AWG gauge, or find the minimum gauge needed for a given current load.
- Choose a mode. Select "Look up by AWG gauge" to see specs for a specific wire size, or "Find gauge by amperage" to get a recommendation based on current.
- Enter your value. Either select the AWG gauge from the dropdown, or enter the current in amps your circuit will carry.
- Read the results. You get the gauge, wire diameter in mm and inches, resistance per 1000 feet, and maximum safe ampacity for chassis wiring.
About AWG Wire Gauges
The American Wire Gauge (AWG) system assigns numbers to wire sizes, with a counterintuitive convention: larger numbers mean thinner wire. AWG 40 is extremely thin (used in windings and sensors), while AWG 0000 (4/0) is a very thick wire used in high-current power distribution.
The ampacity values shown are for chassis wiring (copper conductors in free air). For wiring inside conduit or bundled cables, derate by 80%. For building wiring, always consult the National Electrical Code (NEC) and local codes, as conduit fill, temperature ratings, and insulation type all affect allowed current.
Frequently Asked Questions
What AWG wire do I need for a 20 amp circuit?
For a 20 amp household circuit in the US, the NEC requires a minimum of 12 AWG copper wire with a 20 amp breaker. AWG 12 has a chassis wiring ampacity of 20 A. For 15 amp circuits, AWG 14 is the minimum. Always use wire rated for the breaker size, and use the next larger wire (lower AWG number) for runs over 50 to 100 feet to minimize voltage drop.
What is the difference between AWG and mm² wire sizing?
AWG (American Wire Gauge) is the standard used in the US, while mm² (cross-sectional area in square millimeters) is used in Europe and most other countries. Common conversions: AWG 14 ≈ 2.5 mm², AWG 12 ≈ 4 mm², AWG 10 ≈ 6 mm², AWG 8 ≈ 10 mm². For precise conversions, use the diameter from this calculator to compute the cross-sectional area (π × r²).
Does wire length affect the gauge I should use?
Yes. Longer wire runs have more resistance, causing voltage drop that reduces available voltage at the load. For runs over 50 feet, consider using a wire one or two gauges heavier (lower AWG number) than the minimum for ampacity. Use the Voltage Drop Calculator to determine how much voltage is lost on your specific run and whether it is within acceptable limits (typically less than 3% for power circuits).
Can I use a thicker wire than required?
Yes, using a thicker wire (lower AWG number) than the minimum required is always safe and often beneficial. It reduces voltage drop, generates less heat, and handles future load increases. The only downsides are higher material cost and that thicker wire can be harder to route through conduit or small spaces. There is no electrical penalty for over-sizing wire.