To convert mm to inches you need to divide the value in mm by 25.4 as there are this many millimeters in an inch.
MM to Inches Converter (mm → in) – Free Online Calculator & Complete Guide
MM to Inches Converter turns any value in millimeters (mm) into inches (in) using the exact rule inches = millimeters ÷ 25.4. This page explains the formula in simple words, shows step-by-step examples, gives quick charts, answers common questions, and shares pro tips for rounding and real-world use. Whether you’re shopping, building, or reading specs, you’ll get fast, accurate results—every time.
Quick answer (for the featured snippet)
How do you convert mm to inches?
Use the exact formula: inches = millimeters ÷ 25.4.
Example: 90 mm ÷ 25.4 = 3.5433 in (≈ 3 9/16 in).
Why you need an MM to Inches Converter
Millimeters are standard in the metric world (parts, 3D prints, VESA patterns, global size charts). Inches are common in U.S. customary/imperial contexts (woodworking, screens, many retail specs). When specs don’t match your measuring tools, precise conversion prevents wrong orders, returns, and rework. A good converter should be instant, mobile-friendly, and transparent about the math so you can trust the output.
The exact formula (no approximations)
By international definition: 1 inch = 25.4 millimeters. Because this is exact, dividing any mm value by 25.4 gives the correct answer in inches. After that, choose a display style (decimals or fractions) that matches your task.
Formula: inches = millimeters ÷ 25.4
Examples:
- 50 mm → 50 ÷ 25.4 = 1.9685 in → show as 1.97 in (2 d.p.) or ≈ 2 in (nearest 1/16″)
- 90 mm → 90 ÷ 25.4 = 3.5433 in → 3.54 in (2 d.p.) or ≈ 3 9/16 in
Mini mm → inches chart (10 to 200 mm)
| mm | in (≈) | mm | in (≈) |
|---|---|---|---|
| 10 | 0.3937 | 110 | 4.3307 |
| 20 | 0.7874 | 120 | 4.7244 |
| 30 | 1.1811 | 130 | 5.1181 |
| 40 | 1.5748 | 140 | 5.5118 |
| 50 | 1.9685 | 150 | 5.9055 |
| 60 | 2.3622 | 160 | 6.2992 |
| 70 | 2.7559 | 170 | 6.6929 |
| 80 | 3.1496 | 180 | 7.0866 |
| 90 | 3.5433 | 190 | 7.4803 |
| 100 | 3.9370 | 200 | 7.8740 |
Need another value? Use mm ÷ 25.4 or the converter on this page.
FAQ MM to Inches Converter
Is 25.4 mm exactly 1 inch?
Yes. By definition 1 in = 25.4 mm (exact), so ÷ 25.4 is always correct.
What is the best way to convert mm to inches?
Use inches = millimeters ÷ 25.4. Example: 90 mm ÷ 25.4 = 3.5433 in.
Should I display decimals or fractions?
Use 2 decimals for shopping/specs; use nearest 1/16″ (or 1/64″ for fine work) for woodworking and plans.
Why do different sites show slightly different numbers?
Rounding at different steps. Do your math at full precision and round once at the end. That keeps totals consistent.
Is 25 mm the same as 1 inch?
No. 25 mm ≈ 0.9843 in. You need 25.4 mm for exactly 1 in.
How do I convert inches back to millimeters?
Multiply inches by 25.4. Example: 12 in × 25.4 = 304.8 mm.
What’s the quickest mental estimate without a calculator?
Divide by 25 for a rough value, then shave a little off (because the real divisor is 25.4). Confirm with ÷ 25.4 before cutting or ordering.
Can I show feet + inches?
Yes. Convert to total inches first, then split: feet = floor(in ÷ 12), remainder = in − feet × 12. Round the remainder last.
Conclusion
You only need one rule to convert perfectly: inches = millimeters ÷ 25.4. From that exact definition, choose the output style that suits your job—two decimals for specs, fractional inches for builds—then round once at the end and allow a little clearance for real-world fits. Add feet-and-inches formatting for large values, keep your page fast and mobile-friendly, and be transparent about the calculation. With this approach, your millimeters to Inches Converter page will be more useful, more trustworthy, and better positioned to rank.