Inches to MM Converter
Convert inches to millimeters instantly — perfect for engineering, hardware, and precision measurements.
Conversion table
| Measurement | Millimeters | Centimeters | Meters |
|---|---|---|---|
| 0.5 | 12.7 mm | 1.27 cm | 0.0127 m |
| 1 | 25.4 mm | 2.54 cm | 0.0254 m |
| 1.5 | 38.1 mm | 3.81 cm | 0.0381 m |
| 2 | 50.8 mm | 5.08 cm | 0.0508 m |
| 2.5 | 63.5 mm | 6.35 cm | 0.0635 m |
| 3 | 76.2 mm | 7.62 cm | 0.0762 m |
| 4 | 101.6 mm | 10.16 cm | 0.1016 m |
| 5 | 127 mm | 12.7 cm | 0.127 m |
| 6 | 152.4 mm | 15.24 cm | 0.1524 m |
| 7 | 177.8 mm | 17.78 cm | 0.1778 m |
| 8 | 203.2 mm | 20.32 cm | 0.2032 m |
| 9 | 228.6 mm | 22.86 cm | 0.2286 m |
| 10 | 254 mm | 25.4 cm | 0.254 m |
| 12 | 304.8 mm | 30.48 cm | 0.3048 m |
| 15 | 381 mm | 38.1 cm | 0.381 m |
💡 Precision Tips
- Multiply inches by 25.4 to get mm — this is an exact conversion.
- Common fractions: 1/16" = 1.588 mm, 1/8" = 3.175 mm, 1/4" = 6.35 mm.
- Drill bits: #30 = 3.26 mm, 1/8" = 3.175 mm, #7 = 5.11 mm.
- Sheet metal gauge: 18 ga = 1.27 mm, 16 ga = 1.52 mm, 14 ga = 1.90 mm.
How to Convert Inches to Millimeters
The Inches to MM Formula
Common Inches to MM Conversions
- 1/16" = 1.5875 mm — smallest common fraction
- 1/8" = 3.175 mm — common in hardware and plumbing
- 1/4" = 6.35 mm — very common bolt and screw size
- 3/8" = 9.525 mm — close to 10mm metric
- 1/2" = 12.7 mm — standard pipe and hardware size
- 1" = 25.4 mm exactly — the fundamental conversion
Drill Bit Size Conversions
- 1/16" = 1.588 mm — smallest common drill bit
- 3/32" = 2.381 mm — fine pilot holes
- 1/8" = 3.175 mm — standard pilot hole
- 3/16" = 4.763 mm — medium-small holes
- 1/4" = 6.350 mm — standard through-holes
- 3/8" = 9.525 mm — large through-holes
Inches to MM Examples
Step-by-step conversions
Convert 3/8" bolt to mm
- 3/8 = 0.375 inches
- 0.375 × 25.4 = 9.525 mm
- Closest metric: 10 mm bolt
- Difference: 10 - 9.525 = 0.475 mm
- NOT interchangeable for precision
3/8" = 9.525 mm (≈ 10 mm metric)
Convert 2.5" pipe diameter to mm
- 2.5 × 25.4 = 63.5 mm
- Standard metric pipe: 65 mm
- Or DN65 (nominal diameter)
- 2.5" is a common US pipe size
2.5" = 63.5 mm
Frequently Asked Questions
How many mm is 1 inch?
1 inch equals exactly 25.4 millimeters. This is an exact definition established by international agreement in 1959, not an approximation.
How do I convert inch fractions to mm?
Convert the fraction to decimal first, then multiply by 25.4. Examples: 1/8" = 0.125 × 25.4 = 3.175 mm. 5/16" = 0.3125 × 25.4 = 7.938 mm. 3/4" = 0.75 × 25.4 = 19.05 mm.
Can I use a 10mm wrench on a 3/8" bolt?
A 3/8" bolt is 9.525 mm, so a 10mm wrench is 0.475 mm larger — it may work but can round off bolt heads over time. For precision work, always use the correct size. Metric and imperial wrenches are close but not interchangeable.
What is a mil or thou?
A mil (also called thou) is 1/1000 of an inch = 0.0254 mm = 25.4 micrometers. It's used in manufacturing, PCB design, and thin material measurements. To convert mils to mm, multiply by 0.0254.
How thick is 1mm in inches?
1 mm = 0.03937 inches ≈ 1/25 of an inch, or about 39.4 mils. For context, a credit card is about 0.76 mm (0.030") thick, and a US dime is about 1.35 mm (0.053") thick.
What are standard drill bit sizes in mm?
US drill bits come in fractional inches (1/16" increments), number sizes (#1-80), and letter sizes (A-Z). Common conversions: 1/8" = 3.175 mm, 1/4" = 6.35 mm, 3/8" = 9.525 mm, 1/2" = 12.7 mm. Metric drill bits go in 0.5mm increments: 3.0, 3.5, 4.0, 4.5, 5.0 mm, etc.