gauge to mil Converter
A 14 gauge wire is about 64.08 mils thick, and 64.08 mils is 1.628 mm.
Quick answer: Multiply 5 by 92 raised to the power of (36 minus the gauge) over 39. For example, 14 AWG is 64.084 mils, 12 AWG is 80.808 mils and 18 AWG is 40.303 mils.
The gauge to mil formula
Diameter in mils equals 5 times 92 raised to the power of (36 minus the gauge) divided by 39.
A mil is one thousandth of an inch.
Take 14 AWG. 5 × 92^((36 − 14) ÷ 39) gives 64.084 mils.
Take 12 AWG. 5 × 92^((36 − 12) ÷ 39) gives 80.808 mils.
What a mil is
A mil, also called a thou, is one thousandth of an inch. It equals 0.0254 mm, or 25.4 micrometres (Wikipedia: Thousandth of an inch).
The AWG rule gives 0.005 inches for 36 gauge, which is 5 mils, and each lower gauge number multiplies the size by about 1.1229 (Engineering ToolBox: AWG wire gauge vs circular mils).
How to convert gauge to mil step by step
- Confirm that the wire uses the American Wire Gauge.
- Subtract the gauge number from 36 and divide by 39.
- Raise 92 to that power and multiply by 5 for mils.
- Multiply the mils by 0.0254 for millimetres.
Example 1: 14 AWG
- Start with 14 AWG.
- 5 × 92^((36 − 14) ÷ 39) = 64.084.
- The thickness is 64.084 mils.
14 AWG = 64.084 mils
Example 2: 12 AWG
- Start with 12 AWG.
- 5 × 92^((36 − 12) ÷ 39) = 80.808.
- The thickness is 80.808 mils.
12 AWG = 80.808 mils
Example 3: 18 AWG
- Start with 18 AWG.
- 5 × 92^((36 − 18) ÷ 39) = 40.303.
- The thickness is 40.303 mils.
18 AWG = 40.303 mils
The three examples below use common sizes.
Each one shows the sum in full.
gauge to mil conversion table
| Gauge | Diameter (mils) | Diameter (mm) |
|---|---|---|
| 4 AWG | 204.31 mils | 5.189 mm |
| 6 AWG | 162.02 mils | 4.115 mm |
| 8 AWG | 128.49 mils | 3.264 mm |
| 10 AWG | 101.9 mils | 2.588 mm |
| 12 AWG | 80.808 mils | 2.053 mm |
| 14 AWG | 64.084 mils | 1.628 mm |
| 16 AWG | 50.821 mils | 1.291 mm |
| 18 AWG | 40.303 mils | 1.024 mm |
| 20 AWG | 31.961 mils | 0.8118 mm |
| 22 AWG | 25.347 mils | 0.6438 mm |
| 24 AWG | 20.101 mils | 0.5106 mm |
| 26 AWG | 15.941 mils | 0.4049 mm |
| 28 AWG | 12.641 mils | 0.3211 mm |
The highlighted row is the default of the calculator. The last column gives mm.
A quick mental shortcut for gauge to mil
Remember that 36 AWG is 5 mils and 24 AWG is about 20 mils.
Every 6 gauge steps halve or double the number of mils.
Mil is not mm
In North America a mil means one thousandth of an inch. It is also used as a short form of millimetre, and a millimetre is about 39 mils (Wikipedia: Thousandth of an inch).
The word thou avoids the mix up.
Worked values
A 10 AWG wire is about 101.9 mils, and a 12 AWG wire is about 80.8 mils.
An 18 AWG wire is about 40.3 mils, and a 22 AWG wire is about 25.3 mils.
Mils and circular mils
Circular mils are the diameter in mils squared (Engineering ToolBox: AWG wire gauge vs circular mils). So 64.08 mils gives about 4,107 circular mils for 14 AWG.
The circular mils page works this out for any diameter.
Where thou is used
Wire, foil, film and sheet are often quoted in thou in non-metric countries (Wikipedia: Thousandth of an inch).
Use the mm column when a drawing is in metric.
Quick conversion answers
| Conversion | Result |
|---|---|
| 14 AWG | 64.084 mils |
| 12 AWG | 80.808 mils |
| 18 AWG | 40.303 mils |
| 10 AWG | 101.9 mils |
Where this conversion is used
Cable and PCB specs quote wire and trace sizes in thou.
Makers compare wire to a thou gauge or feeler set.
Common mistakes to avoid
- Reading mil as millimetre. A mm is about 39 mils.
- Assuming a higher gauge is thicker. A higher gauge is thinner.
- Mixing mils with circular mils. One is length and the other is area.
- Using the formula for sheet steel. Steel has its own table.
Related converters
Odd gauge sizes
3 AWG is 229.4 mils. 5 AWG is 181.9 mils. 7 AWG is 144.3 mils.
9 AWG is 114.4 mils. 11 AWG is 90.74 mils. 13 AWG is 71.96 mils.
15 AWG is 57.07 mils. 17 AWG is 45.26 mils. 19 AWG is 35.89 mils.
Thin wire sizes in mils
24 AWG is 20.1 mils. 26 AWG is 15.94 mils. 28 AWG is 12.64 mils.
30 AWG is 10.03 mils. 32 AWG is 7.95 mils. 34 AWG is 6.305 mils.
Worked examples in mils
Take 14 AWG. Subtract 14 from 36 to get 22, and 22 divided by 39 is about 0.5641. Then 92 to that power is about 12.82, and times 5 gives about 64.08 mils.
Take 16 AWG. The same steps give 92 to the power of 0.5128, which is about 10.16, and times 5 gives about 50.8 mils.
From mils to millimetres
Multiply the mils by 0.0254. So 64.08 mils is about 1.628 mm, and 50.82 mils is about 1.291 mm.
A 22 AWG wire at about 25.35 mils is about 0.644 mm. The mm column in the table does this step for you.
A quick mil chart
A 10 AWG wire is about 101.9 mils and a 12 AWG wire is about 80.8 mils. An 18 AWG wire is about 40.3 mils and a 20 AWG wire is about 32.0 mils.
A 24 AWG wire is about 20.1 mils and a 28 AWG wire is about 12.6 mils. A 30 AWG wire is about 10.0 mils.
Notice that 30 AWG is half of 24 AWG, which fits the six step rule.
Frequently asked questions
How many mils is 14 gauge wire?
About 64.08 mils.
How many mils is 12 gauge wire?
About 80.8 mils.
What is a mil?
One thousandth of an inch, or 0.0254 mm.
Is a mil the same as a mm?
No. A millimetre is about 39 mils.
How many mils is 36 gauge?
Exactly 5 mils by the AWG rule.
How do I go from mils back to gauge?
Use the mils to gauge calculator.
Sources
- Wikipedia: Thousandth of an inch (en.wikipedia.org)
- Engineering ToolBox: AWG wire gauge vs circular mils (engineeringtoolbox.com)
