Millimeters to Inches
Convert millimeter to inch instantly — type a value and read the result, with the exact formula shown.
Reviewed by the CalcCafe editorial team · Last updated 1 July 2026 · How we test our tools
Example
1 mm = 0.03937008 in, 5 mm = 0.1968504 in, 10 mm = 0.3937008 in.
Common conversions: millimeter to inch
Quick reference for the mm → in values you are most likely to need, computed with the exact factor the converter above uses. It includes the specific values people most often look up (100 mm, 45 mm, 10 mm, 400 mm, 150 mm). See also the reverse converter: Inch to Millimeter.
| Millimeter (mm) | Inch (in) |
|---|
| 1 mm | 0.03937 in |
| 2 mm | 0.07874 in |
| 3 mm | 0.11811 in |
| 5 mm | 0.19685 in |
| 10 mm | 0.393701 in |
| 15 mm | 0.590551 in |
| 20 mm | 0.787402 in |
| 25 mm | 0.984252 in |
| 30 mm | 1.1811 in |
| 40 mm | 1.5748 in |
| 45 mm | 1.7717 in |
| 50 mm | 1.9685 in |
| 60 mm | 2.3622 in |
| 70 mm | 2.7559 in |
| 75 mm | 2.9528 in |
| 80 mm | 3.1496 in |
| 90 mm | 3.5433 in |
| 100 mm | 3.937 in |
| 150 mm | 5.9055 in |
| 200 mm | 7.874 in |
| 250 mm | 9.8425 in |
| 400 mm | 15.748 in |
| 500 mm | 19.685 in |
| 1,000 mm | 39.3701 in |
Inch to Millimeter
| Inch (in) | Millimeter (mm) |
|---|
| 1 in | 25.4 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 50 in | 1,270 mm |
| 100 in | 2,540 mm |
How it works
Inch = Millimeter × 0.03937008. Every value is converted through a single meter base unit using internationally defined conversion factors, so any from/to pair stays consistent.
Good to know
Going from millimeters to inches is one of the most common everyday conversions for anyone working between a metric spec sheet and an imperial toolbox. It comes up when you read a screw or bolt size stamped in mm but need to buy an imperial drill bit, when a phone or laptop is listed at 7.5 mm thick but you think in fractions of an inch, or when a 3D-printing model, PCB footprint, or piece of jewelry is dimensioned in millimeters and your calipers or ruler are marked in inches.
The two units sit on opposite sides of the measurement world. The millimeter is one-thousandth of a meter, the base length unit of the metric (SI) system used almost everywhere outside the United States. The inch is an imperial/US-customary unit, and since 1959 it has been defined as exactly 25.4 mm — so the relationship is not an approximation but a fixed legal definition. That makes 1 mm equal to exactly 0.03937008 in (the reciprocal of 25.4).
For quick mental math, a handy rule of thumb is that 25 mm is almost exactly 1 inch, so you can divide millimeters by 25 to get a fast estimate that runs only about 1.6% high. Two even simpler anchors worth memorizing: 1 mm is roughly 1/25 inch, and any round centimeter figure is easy too, since 10 mm sits right between 3/8 in (9.525 mm) and 13/32 in.
- Common pitfall: don't confuse millimeters with centimeters — a value given in cm is 10× larger, and mixing them up makes your inch result off by a factor of ten.
- Precision note: for fasteners and machining, round to at least 3 decimal places (thousandths of an inch), since shaving a result like 0.3937 in down to 0.39 in can already exceed a tight tolerance.
Frequently asked questions
How do you convert millimeter to inch?
Multiply the number of millimeters by 0.03937008 to get inches. For example, 1 mm = 0.03937008 in.
What is 1 millimeter in inches?
1 millimeter equals 0.03937008 inches (1 mm = 0.03937008 in).
How many millimeters are in 1 inch?
There are 25.4 millimeters in 1 inch.
Is this converter free and private?
Yes. It runs entirely in your browser, so your inputs never leave your device, there is no sign-up, and it works offline once loaded.
Are the conversions exact?
Conversions use internationally defined factors and are exact where the definitions are exact (for example, 1 inch = 2.54 cm). Displayed results are rounded for readability.
People also ask
What is 10 mm in inches?
10 mm equals 0.3937008 inches, which is just under 13/32 of an inch. A quick estimate is 10 divided by 25, giving about 0.4 in.
How many mm is 1/4 inch?
One quarter inch is 6.35 mm exactly, since a full inch is 25.4 mm and 25.4 divided by 4 equals 6.35.
Is 5 mm the same as 1/4 inch?
No. 5 mm is about 0.1969 in (roughly 13/64 in), while a true quarter inch is 6.35 mm, so 5 mm is noticeably smaller.
How do I convert mm to inches without a calculator?
Divide the millimeter value by 25.4, or for a fast rough answer divide by 25. For example, 50 mm is about 50/25 = 2 in (the exact value is 1.9685 in).
What is 3 mm in inches?
3 mm is 0.1181 in, which is very close to 1/8 inch (0.125 in) but slightly smaller. It is closest to a 1/8 in or 7/64 in fraction.
How thick is 2 mm in inches?
2 mm equals about 0.0787 in, or roughly 5/64 of an inch — close to the thickness of two stacked credit cards.
What size in inches is 20 mm?
20 mm is 0.7874 in, which is just under 51/64 in or about 25/32 in. A handy mental check is 20/25 = 0.8 in.
Why is an inch exactly 25.4 mm?
In 1959 the US and Commonwealth countries adopted the international yard and pound agreement, defining the inch as precisely 25.4 mm. This made conversions between the two systems exact rather than approximate.
Related calculators
Sources & references
These tools follow our methodology and provide educational estimates only — verify important figures with a qualified professional.