About the Wire Gauge Calculator
Wire Gauge Calculator converts between the American Wire Gauge (AWG) number of a wire and its metric size. Enter an AWG number such as 12 or 4/0 to see the diameter in millimetres and inches, the cross-section area in mm², the size in circular mils and the resistance of a copper wire per kilometre and per 1,000 feet. Or enter a diameter in millimetres or an area in mm² to find the nearest AWG size, with a note on whether it is an exact standard size. The range covers 4/0 (0000) through 40. The values come from the AWG formula, which is the basis of the standard tables, so they match published charts to the rounding shown. Resistance is for solid copper at 20 degrees Celsius. The tool does not give safe current ratings, because those depend on insulation, temperature and installation.
Updated September 2026
How to use the Wire Gauge Calculator
- 1Choose whether you know the AWG number, the diameter in mm or the area in mm².
- 2Type the value, or tap one of the common gauge buttons.
- 3Read the AWG, diameter, area and circular mils.
- 4Look at the resistance per kilometre and per 1,000 feet for copper.
- 5If you started from a size in mm or mm², check whether the result is an exact size or the nearest one.
How the AWG scale works
The AWG scale is based on the number of steps that were once needed to draw a wire down to size: a thinner wire went through more drawing dies, so it has a bigger number. The scale is exact and geometric. From 4/0 (diameter 0.46 inches) to 36 AWG (0.005 inches) there are 39 steps, and each step changes the diameter by about 12.2 percent.
That gives some useful rules of thumb: every 3 gauges the area doubles or halves, every 6 gauges the diameter doubles or halves, and every 10 gauges the area changes by a factor of about ten.
Typical uses
- 24 to 28 AWG: phone, network and small signal wires.
- 22 to 18 AWG: hobby electronics, speaker wire and low-power lighting.
- 16 to 14 AWG: extension cords and small appliances.
- 12 to 10 AWG: household circuits in the US, such as outlets and small motors.
- 8 AWG and thicker: cooker circuits, sub-panels, car batteries, welding cable and service cables.
Resistance and length
Thinner wire has more resistance, and copper at 20 degrees has about 5.2 ohms per kilometre at 3.31 mm² (12 AWG) and 21 ohms per kilometre at 0.82 mm² (18 AWG). That is why long runs of thin wire lose voltage. The resistance shown per kilometre and per 1,000 feet lets you estimate the loss yourself: multiply by the length in those units and by the current to get the voltage.
Wire made of other metals has other resistance. Aluminium has about 1.6 times the resistance of copper for the same size, which the Voltage Drop Calculator takes into account.
Tips and related tools
When you buy cable in a country that uses square millimetres, choose the standard size that is at least as large as the area you need, not the nearest one, unless the result says it is exact. To work out power, current and voltage from each other, use Watts, Amps and Volts Calculator or Ohm's Law Calculator.
Unit Converter converts lengths between millimetres and inches, and Resistor Color Code Calculator reads the resistors that often go with such wires in electronics projects.
Features
- AWG to diameter, area and circular mils
- Diameter or area to the nearest AWG
- 4/0 (0000) to 40 AWG
- Copper resistance per km and per 1,000 ft
- Shows if a size is exact or nearest
- Tap buttons for common gauges
- Table of common sizes
Frequently asked questions
What is AWG?
American Wire Gauge is a system for naming the size of round wire. A higher number means a thinner wire: 24 AWG is thin, like a phone cable, and 10 AWG is thick, like a wire for a power outlet. Each step of 6 gauges roughly halves the diameter, and 3 gauges roughly halve the area.
How do I convert AWG to mm?
Use the formula diameter in mm = 0.127 × 92^((36 − n) ÷ 39), where n is the gauge. For 12 AWG that gives 2.053 mm, and the area is 3.31 mm². Type the gauge above to get the values without doing the maths.
How do I convert mm² to AWG?
Work out the diameter from the area, then apply the reverse of the formula. As a quick guide, 1.5 mm² is about 15 AWG, 2.5 mm² about 13 AWG, 4 mm² about 11 AWG and 6 mm² about 9 AWG. The tool finds the nearest gauge and tells you whether it is an exact match.
What does 4/0 AWG mean?
Sizes larger than 1 AWG are named 1/0, 2/0, 3/0 and 4/0, said 'one-aught' to 'four-aught'. Also written 0, 00, 000 and 0000. 4/0 AWG has a diameter of 11.68 mm and an area of 107.2 mm². You can type either form.
Can I use this to choose a wire for a circuit?
Not by itself. The size a circuit needs depends on the current, the length, the type of insulation and how the wire is installed, and local wiring rules set the limits. Use Voltage Drop Calculator to check how much voltage a run loses, and a current rating table from your regulations for the safe current.
Why are stranded wires different?
The AWG number refers to the total copper cross-section, so a stranded wire of the same gauge as a solid one has the same area, but its overall diameter is a little larger because of gaps between the strands. The resistance shown is for the copper area.