Convert Inches to mm
Convert inches to millimeters instantly — exact factors, common-value table, nothing uploaded.
Common conversions
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Inches to millimeters, imperial specs in metric parts
When an imperial drawing meets a metric workshop, everything funnels through one number: 1 inch = 25.4 millimeters, exactly. Half an inch is 12.7 mm, a quarter inch is 6.35 mm, and every fraction in between is just multiplication.
This page presets the converter to inches → millimeters. Type 0.375 (a 3/8 fitting) and you get 9.525 mm immediately — no table hunting, no rounding games.
Because the factor is exact, converted dimensions are as precise as the original spec. The quick table below covers the common fractions and round inches; the converter handles everything else as you type, entirely in your browser.
Quick conversion table
Common values at a glance — computed locally with exact standard factors.
| Value (in) | Converted (mm) |
|---|---|
| 1 | 25.4 |
| 2 | 50.8 |
| 5 | 127 |
| 10 | 254 |
| 25 | 635 |
| 50 | 1270 |
| 100 | 2540 |
How to convert inches to mm
Enter inches as a decimal
Convert fractions first: 3/4 becomes 0.75, 5/32 becomes 0.15625.
Read the result in mm
Exact multiplication by 25.4 — no approximation at any step.
Flip direction anytime
The swap button turns this into mm-to-inches without losing your value.
FAQs about this conversion
How many mm is 1 inch exactly?
Exactly 25.4 mm — the definition has been fixed internationally since 1959.
What is 1/4 inch in mm?
0.25 in × 25.4 = 6.35 mm. Common metric drills at 6 mm and 6.5 mm bracket it closely.
Do I need to worry about US vs imperial inches?
No — since 1959 US and imperial inches are the same unit, 25.4 mm exactly.
Other conversions
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