inch to mm Converter
Convert inch to mm instantly. This page also covers inches to mm, inches to millimeters, and convert inches to mm — same factor: 1 in = 25.4 mm exactly. Type a decimal or a fraction (1/2, 5/8, 1 1/2, 2 1/2).
- Millimeters
- 25.4
- Decimal inches
- 1.0000
- Nearest 1/64
- 1 in (exact on 1/64)
- Feet + inches
- 0 ft 1.000 in
The inches fraction result is rounded to the nearest 1/64 fraction.
inch to mm conversion
The international inch is defined exactly as 25.4 mm. For inch to mm conversion use:
1 in = 25.4 mm · 1 mm = 0.0393701 in
Step-by-step conversion (example: 1 inch)
- Start with the length in inches: 1 in.
- Multiply by 25.4: 1 × 25.4 = 25.4 mm.
- Reverse check: 25.4 ÷ 25.4 = 1 — the conversion round-trips cleanly.
Another example: 5 inches × 25.4 = 127 mm; 10 inches = 254 mm.
inch to mm calculator
Use the bidirectional calculator at the top. Type inches as a decimal or a fraction; millimeters update from the same engine as the mm to inches hub. 1 mm = 0.0394 in.
inch to mm chart
Fractional inches first (the high-volume shop sizes), then whole inches. Linked rows have dedicated pages. 2 1/2 inches to mm is the same length as 2.5 in ( 63.5 mm).
| Inches | Millimeters | Page |
|---|---|---|
| 1/64 in | 0.3969 mm | use converter |
| 1/32 in | 0.7937 mm | use converter |
| 1/16 in | 1.5875 mm | use converter |
| 1/8 in | 3.175 mm | use converter |
| 1/4 in | 6.35 mm | 1/4 inch to mm |
| 5/16 in | 7.9375 mm | 5/16 inch to mm |
| 3/8 in | 9.525 mm | 3/8 inch to mm |
| 1/2 in | 12.7 mm | 1/2 inch to mm |
| 5/8 in | 15.875 mm | 5/8 inch to mm |
| 3/4 in | 19.05 mm | 3/4 inch to mm |
| 7/8 in | 22.225 mm | use converter |
| 1 in | 25.4 mm | use converter |
| 1 1/4 in | 31.75 mm | 1 1/4 inches to mm |
| 1 1/2 in | 38.1 mm | 1 1/2 inches to mm |
| 1 5/8 in | 41.275 mm | 1 5/8 inches to mm |
| 2 1/2 in | 63.5 mm | 2 1/2 inches to mm |
| Inches | Millimeters |
|---|---|
| 1 inch | 25.4 mm |
| 2 inches | 50.8 mm |
| 3 inches | 76.2 mm |
| 4 inches | 101.6 mm |
| 5 inches | 127 mm |
| 6 inches | 152.4 mm |
| 7 inches | 177.8 mm |
| 8 inches | 203.2 mm |
| 9 inches | 228.6 mm |
| 10 inches | 254 mm |
| 12 inches | 304.8 mm |
Common conversions
Dedicated fraction pages. Each reuses the same 25.4 mm inch. High-volume sizes: 1 1/2 inches to mm and 2 1/2 inches to mm (2.5 in).
Related length converters
References
Conversion on this page uses the international inch (exactly 25.4 mm). Primary sources:
- NIST — SI Units: Length — since the 1959 yard agreement, the standard inch is exactly equivalent to 25.4 mm.
- Federal Register Notice 59-5442 (PDF) — July 1, 1959 announcement of the international yard and the inch = 25.4 mm exactly.
- NIST Guide to the SI, Appendix B — conversion factors based on the international foot/inch (1 in = 0.0254 m exactly).
FAQ
1 1/2 inches is 38.1 mm ; 2 1/2 inches is 63.5 mm ; 1/4 inch is 6.35 mm ; 1/2 inch is 12.7 mm ; 5/8 inch is 15.875 mm ; 5/16 inch is 7.9375 mm ; 1.5 inch is 38.1 mm ; 1 1/4 inches is 31.75 mm ; 1 5/8 inches is 41.275 mm ; 3/8 inch is 9.525 mm ; 3/4 inch is 19.05 mm .
How many millimeters in an inch
One inch is equal to 25.4 millimeters exactly. That is the international-inch definition (1959 yard agreement / Federal Register 59-5442), not a rounded measurement.
How many inches in a millimeter
One millimeter is 1 ÷ 25.4 = 0.03937 in (0.0394 in to four decimals). Reverse of inch to mm: divide millimeters by 25.4.
How to convert inches to millimeters
Multiply the inch value by 25.4. Example: 5 in × 25.4 = 127 mm; 10 in × 25.4 = 254 mm. Convert a fraction to a decimal first: 1/2 in = 0.5 in = 12.7 mm.
How many mm in an inch?
There are 25.4 mm in an inch. 25 mm is 0.4 mm short of 1 inch (25 mm = 0.9843 in).
How to convert 10 inches to millimeters
Multiply 10 inches by 25.4: 10 × 25.4 = 254 mm.
How many mm is 1/2 inch?
1/2 inch is 12.7 mm exactly (0.5 × 25.4). 12 mm is 0.7 mm smaller; 13 mm is 0.3 mm larger.