MM to Inches Converter
Convert millimeters to inches instantly — essential for engineering, manufacturing, and precision work.
Conversion table
| Measurement | Inches (decimal) | Inches (fraction) | Centimeters |
|---|---|---|---|
| 0.5 | 0.0197 in | ≈ 1/64" | 0.05 cm |
| 1 | 0.0394 in | ≈ 3/64" | 0.1 cm |
| 1.5 | 0.0591 in | ≈ 1/16" | 0.15 cm |
| 2 | 0.0787 in | ≈ 5/64" | 0.2 cm |
| 2.5 | 0.0984 in | ≈ 3/32" | 0.25 cm |
| 3 | 0.1181 in | ≈ 1/8" | 0.3 cm |
| 4 | 0.1575 in | ≈ 5/32" | 0.4 cm |
| 5 | 0.1969 in | ≈ 13/64" | 0.5 cm |
| 6 | 0.2362 in | ≈ 15/64" | 0.6 cm |
| 7 | 0.2756 in | ≈ 9/32" | 0.7 cm |
| 8 | 0.315 in | ≈ 5/16" | 0.8 cm |
| 9 | 0.3543 in | ≈ 23/64" | 0.9 cm |
| 10 | 0.3937 in | ≈ 25/64" | 1 cm |
| 12 | 0.4724 in | ≈ 15/32" | 1.2 cm |
| 15 | 0.5906 in | ≈ 19/32" | 1.5 cm |
💡 Precision Tips
- 1 inch = exactly 25.4 mm — divide mm by 25.4 to get inches.
- Quick estimate: divide mm by 25 for a rough inch value.
- Common wrench sizes: 10mm ≈ 3/8", 13mm ≈ 1/2", 19mm ≈ 3/4".
- 1 mil (thou) = 0.001 inches = 0.0254 mm — used in manufacturing.
How to Convert MM to Inches
The MM to Inches Formula
Common MM to Inches Conversions
- 1 mm = 0.03937 in = ~1/25" — about the thickness of a credit card
- 3.175 mm = 1/8 inch exactly
- 6.35 mm = 1/4 inch exactly
- 12.7 mm = 1/2 inch exactly
- 19.05 mm = 3/4 inch exactly
- 25.4 mm = 1 inch exactly — the key reference value
Wrench & Socket Size Equivalents
- 8 mm ≈ 5/16" (0.3125") — small bolt
- 10 mm ≈ 3/8" (0.375") — very common automotive
- 13 mm ≈ 1/2" (0.5") — standard bolt size
- 17 mm ≈ 11/16" (0.6875") — lug nuts, larger bolts
- 19 mm ≈ 3/4" (0.75") — common lug nut size
- 22 mm ≈ 7/8" (0.875") — large industrial bolts
MM to Inches Examples
Step-by-step conversions
Convert 10mm wrench to inches
- 10 ÷ 25.4 = 0.3937 inches
- Nearest fraction: 0.3937 × 16 = 6.3
- Round to 6/16 = 3/8" (0.375")
- Difference: 0.3937 - 0.375 = 0.019"
- 3/8" wrench fits ~10mm bolts
10 mm = 0.394" ≈ 3/8" (close but not exact)
3D print layer height: 0.2mm
- 0.2 ÷ 25.4 = 0.00787 inches
- In mils: 0.2 × 39.37 = 7.87 mils
- This is ~8 thou (thousandths)
- Common range: 0.1-0.3 mm (4-12 thou)
0.2 mm = 0.008" = 7.87 mils
Frequently Asked Questions
How many inches is 1 mm?
1 millimeter equals 0.03937 inches, or approximately 1/25 of an inch. To convert mm to inches, divide by 25.4. To convert inches to mm, multiply by 25.4.
How do I convert mm to fractional inches?
Divide mm by 25.4 to get decimal inches. Then multiply by the denominator you want (16 for 16ths, 32 for 32nds, 64 for 64ths) and round. Example: 10 mm = 0.3937" × 32 = 12.6/32 ≈ 13/32".
What is 25.4 mm in inches?
25.4 mm equals exactly 1 inch. This is the exact definition — 1 inch = 25.4 mm was established by international agreement in 1959.
Is a 10mm wrench the same as 3/8 inch?
Very close but not exact. 10mm = 0.3937" while 3/8" = 0.375" — a difference of 0.019" (0.47 mm). A 3/8" wrench can usually fit a 10mm bolt, but it may be slightly loose. For precision work, use the correct metric or imperial tool.
What is a mil or thou?
A mil (also called thou) is 1/1000 of an inch = 0.0254 mm. It's used in manufacturing for thin materials like sheet metal, wire gauge, paint thickness, and PCB traces. 1 mm = 39.37 mils.
How do I measure mm without a metric ruler?
If you only have an imperial ruler: 1/16" ≈ 1.6 mm, 1/8" ≈ 3.2 mm, 1/4" ≈ 6.4 mm, 1/2" ≈ 12.7 mm, 1" = 25.4 mm. For precise work, use a digital caliper that displays both mm and inches.