Inches to Millimeters (in to mm) Converter

Enter inches, including decimals such as 0.375 for 3/8, to get millimeters.

1 inch = 25.4 mm exactly

From
To
25.4
Try:
Step-by-stepin โ†’ mm
11 in = 25.4 mmformula
21 ร— 25.4substitute
325.4 mmresult
URLiunitconverter.com/length/inches-to-millimeters?value=1Open
1 in in every unit
mm
Millimeter
1 mm = 0.1 cm
25.4 mm
cm
Centimeter
1 cm = 10 mm
2.54 cm
m
Meter
SI base unit
0.0254 m
km
Kilometer
1 km = 1,000 m
0.0000254 km
in
Inch
1 in = 2.54 cm exactly
1 in
ft
Foot
1 ft = 12 in
0.083333333 ft
yd
Yard
1 yd = 3 ft
0.027777778 yd
mi
Mile
1 mi = 5,280 ft
0.000015782828 mi

Inches to Millimeters Formula

millimeters = inches ร— 25.4

One inch is 25.4 millimeters, by definition, so the conversion is exact. For example, 1 in ร— 25.4 = 25.4 mm.

Nominal Sizes Are Not Actual Sizes

Some imperial sizes are names, not measurements. Converting the name gives the wrong answer.

ItemName suggestsActual size
2ร—4 lumber (dried, planed)50.8 ร— 101.6 mm1.5 ร— 3.5 in = 38.1 ร— 88.9 mm
ยฝโ€ณ pipe (NPS), outside diameter12.7 mm0.840 in = 21.3 mm
ยพโ€ณ pipe (NPS), outside diameter19.1 mm1.050 in = 26.7 mm

US Letter vs A4 Paper

North America uses Letter paper, sized in inches. Most other countries use A4, sized in millimeters. A4 is narrower and taller.

PaperInchesMillimeters
US Letter8.5 ร— 11 in215.9 ร— 279.4 mm
A48.27 ร— 11.69 in210 ร— 297 mm

Inches to Millimeters Table

Inches (in)Millimeters (mm)
0.0625 in1.5875 mm
0.125 in3.175 mm
0.1875 in4.7625 mm
0.25 in6.35 mm
0.3125 in7.9375 mm
0.375 in9.525 mm
0.5 in12.7 mm
0.625 in15.875 mm
0.75 in19.05 mm
0.875 in22.225 mm
1 in25.4 mm
1.5 in38.1 mm
2 in50.8 mm
3 in76.2 mm
6 in152.4 mm
12 in304.8 mm

Common Questions

How many millimeters are in an inch?
Exactly 25.4 mm.
What is 1/4 inch in mm?
1/4 inch is 6.35 mm.
What is 3/8 inch in mm?
3/8 inch is 9.525 mm.
Why isn't a 2ร—4 two inches by four inches?
The name is the rough-sawn size. After drying and planing, a 2ร—4 is 1.5 ร— 3.5 inches (38.1 ร— 88.9 mm).