Inch (Diameter) to Millimeter (Diameter) Converter

Wire Gauge Converter

2 units available

Decimals:

From

To

25.4

1 in = 25.4 mm

Formula:

mm = in × 25.4

With your value: 1 in = 25.4 mm

Other Inch (Diameter) to Millimeter (Diameter) conversions

2 in to mm 3 in to mm 4 in to mm 5 in to mm 6 in to mm 7 in to mm 8 in to mm

Inch (Diameter) to Millimeter (Diameter) Conversion Table

Inch (Diameter) (in)	Millimeter (Diameter) (mm)
0.5	12.7
1	25.4
2	50.8
5	127
10	254
15	381
20	508
25	635
50	1,270
100	2,540
250	6,350
500	12,700
1000	25,400

Millimeter (Diameter) to Inch (Diameter) Conversion Table

Millimeter (Diameter) (mm)	Inch (Diameter) (in)
0.5	0.019685
1	0.03937
2	0.07874
5	0.19685
10	0.393701
15	0.590551
20	0.787402
25	0.984252
50	1.968504
100	3.937008
250	9.84252
500	19.685039
1000	39.370079

Where these values come from

Every factor on this page is traced to the document that defines it. See the full provenance dataset or our methodology.

Inch (Diameter) (in)

Wire Gauge

Exact conversion

AWG diameters follow a geometric series between 0.4600 in (AWG 4/0) and 0.0050 in (AWG 36), as specified in ASTM B258.

Source: ASTM B258, Standard Specification for Nominal Diameters of Solid Round Wires

ASTM International · Reviewed 2026-07-01

Millimeter (Diameter) (mm)

Wire Gauge

Exact conversion

AWG diameters follow a geometric series between 0.4600 in (AWG 4/0) and 0.0050 in (AWG 36), as specified in ASTM B258.

Source: ASTM B258, Standard Specification for Nominal Diameters of Solid Round Wires

ASTM International · Reviewed 2026-07-01

How to Convert Inch (Diameter) to Millimeter (Diameter)

To convert from Inch (Diameter) (in) to Millimeter (Diameter) (mm), multiply the value by 25.4.

Formula: mm = in × 25.4

Reverse: in = mm × 0.0393700787

Step-by-Step Example

Start with your value in Inch (Diameter). For example: 5 in
Multiply by the conversion factor: 5 x 25.4
The result is: 127 mm

About Inch (Diameter)

The inch (diameter) (in) is a unit of wire sizing. One inch (diameter) equals 25.4 square millimetre of cross-sections. UnitConvertLab converts it against every other wire gauge unit using this exact definition, so results are reproducible to full double precision rather than rounded lookup tables.

Common uses: wire gauge calculations, engineering and science, education.

About Millimeter (Diameter)

The millimeter (diameter) (mm) is a unit of wire sizing. One millimeter (diameter) equals 1 square millimetre of cross-section. UnitConvertLab converts it against every other wire gauge unit using this exact definition, so results are reproducible to full double precision rather than rounded lookup tables.

Common uses: wire gauge calculations, engineering and science, education.

Frequently Asked Questions

How many Millimeter (Diameter) are in 1 Inch (Diameter)?

There are exactly 25.4 Millimeter (Diameter) in 1 Inch (Diameter). This means the conversion factor from Inch (Diameter) to Millimeter (Diameter) is 25.4.

What is the formula to convert Inch (Diameter) to Millimeter (Diameter)?

The formula to convert Inch (Diameter) to Millimeter (Diameter) is: mm = in × 25.4. For example, to convert 10 Inch (Diameter) to Millimeter (Diameter), you would multiply 10 by 25.4.

What is a Inch (Diameter)?