How to Convert Millimeters to Inches
MM to Inches Conversion Reference Table
Use this quick-reference table for the most commonly searched millimeter-to-inch conversions. All values use the exact international standard (1 inch = 25.4 mm).
| Millimeters (mm) | Inches (decimal) | Nearest Fraction | Common Context |
|---|---|---|---|
| 1 mm | 0.039" | ~1/25" | Credit card thickness |
| 3 mm | 0.118" | ~1/8" | M3 screw diameter |
| 5 mm | 0.197" | ~3/16" | Pencil lead, small screws |
| 6 mm | 0.236" | ~1/4" | M6 bolt diameter |
| 10 mm | 0.394" | ~3/8" | Socket wrench size |
| 12.7 mm | 0.500" | 1/2" | Exact half-inch |
| 19 mm | 0.748" | ~3/4" | Plywood thickness |
| 25 mm | 0.984" | ~1" | Close to 1 inch (off by 0.4 mm) |
| 25.4 mm | 1.000" | 1" | Exact 1 inch |
| 50 mm | 1.969" | ~2" | Camera lens (50 mm) |
| 100 mm | 3.937" | ~4" | 10 cm reference |
Reverse reference (inches to mm): 1/8" = 3.175 mm | 1/4" = 6.35 mm | 1/2" = 12.7 mm | 1" = 25.4 mm | 12" = 304.8 mm
Why Use UtilDaily's MM to Inches Converter?
Millimeters and inches coexist in engineering, woodworking, and manufacturing worldwide. A single misreading — confusing 25 mm with 1 inch, for example — can ruin a part, waste material, or cause a safety issue. Our converter uses the exact international standard (1 inch = 25.4 mm, per NIST SP 811) and shows both decimal and fractional inch results so you can read values directly off an imperial tape measure or caliper.
- Fractional inch display — shows results as practical fractions (1/8", 3/16", 1/4", etc.) used in woodworking, machining, and construction
- Exact conversion — uses the internationally defined 1 inch = 25.4 mm for perfectly accurate results, not approximations
- Bidirectional conversion — switch between mm to inches and inches to mm in one tool
- Paper size reference — quickly convert A4 (210 x 297 mm), Letter, and other standard paper sizes
- Engineering precision — handles decimal places for technical drawings, 3D printing tolerances, and machining specs
- No signup or download — free browser-based tool with instant results on any device
Frequently Asked Questions
How many inches is 1 mm?
1 millimeter equals 0.03937 inches, or approximately 1/25th of an inch. The exact conversion is 1 mm = 1/25.4 inches, based on the international standard that defines 1 inch as exactly 25.4 mm. For a visual reference, 1 mm is roughly the thickness of a credit card (about 0.76 mm) or a dime coin.
How many inches is 10 mm?
10 millimeters equals 0.3937 inches, which is approximately 3/8 inch (0.375 inches). The difference between 10 mm and 3/8 inch is only about 0.5 mm, making them nearly interchangeable in practical applications. This conversion is commonly needed for bolt sizes, jewelry, and socket wrench dimensions — many tool sets include both 10 mm and 3/8-inch sockets.
How many inches is 25 mm?
25 millimeters equals 0.984 inches — very close to 1 inch but not exact. The precise 1-inch mark is at 25.4 mm, so 25 mm falls 0.4 mm (about 1/64 inch) short of a full inch. In practical work, 25 mm is often treated as approximately 1 inch, but for precision machining or engineering, the 0.4 mm difference matters.
How many inches is 50 mm?
50 millimeters equals 1.969 inches, which is approximately 2 inches (with a difference of less than 1 mm). The exact calculation is 50 ÷ 25.4 = 1.96850 inches. In photography, the 50 mm lens (often called a "nifty fifty") is one of the most popular focal lengths, equivalent to roughly a 2-inch lens diameter.
How many inches is 100 mm?
100 millimeters equals 3.937 inches, or approximately 3-15/16 inches. A quick rule of thumb is that 100 mm is almost exactly 4 inches (the difference is only about 1.6 mm). This is also equal to 10 centimeters, making it a useful reference point for converting between metric and imperial measurements.
How many inches is 200 mm?
200 millimeters equals 7.874 inches, or approximately 7-7/8 inches. The calculation is 200 ÷ 25.4 = 7.87402 inches. This measurement is common in photography (200 mm telephoto lens), baking (standard 200 mm / 8-inch cake pan), and various engineering applications.
How many inches is 150 mm?
150 millimeters equals 5.906 inches, or approximately 5-29/32 inches. For practical purposes, 150 mm is very close to 6 inches (the difference is about 2.4 mm). This measurement frequently appears in cooking (150 mm / 6-inch plates), electronics, and construction specifications.
How do I convert mm to inches?
Divide the millimeter value by 25.4 to get inches. For example: 100 mm ÷ 25.4 = 3.937 inches. Alternatively, you can multiply by 0.0393701. The division by 25.4 method is preferred because 25.4 is the exact defined conversion factor. For a quick mental estimate, dividing by 25 gives a result within about 1.6% of the exact answer.
What is 210 mm in inches?
210 millimeters equals 8.268 inches. This is the width of an A4 sheet of paper (the international standard paper size). An A4 sheet measures 210 x 297 mm (8.268 x 11.693 inches), which is slightly narrower and taller than US Letter size paper (8.5 x 11 inches or 215.9 x 279.4 mm).
What is 297 mm in inches?
297 millimeters equals 11.693 inches. This is the height (long edge) of an A4 sheet of paper. Combined with the width of 210 mm (8.268 inches), the A4 format measures 210 x 297 mm. Compared to US Letter paper (11 inches tall), A4 is about 0.693 inches (17.6 mm) taller but 0.232 inches (5.9 mm) narrower.
How many mm is 1 inch?
1 inch equals exactly 25.4 millimeters. This is not an approximation — it is the precise international standard defined by the International Yard and Pound Agreement of 1959. This exact relationship is the foundation for all mm-to-inches conversions: to convert mm to inches, divide by 25.4; to convert inches to mm, multiply by 25.4.
What is 5 mm in inches?
5 millimeters equals 0.197 inches, which is approximately 3/16 of an inch (0.1875 inches). More precisely, 5 mm is closest to 13/64 inch (0.203 inches). In practical use, 5 mm is commonly approximated as 3/16 inch. This measurement is common for jewelry (thin ring bands), small screws, and pencil lead diameters.
Is 5 mm equal to 1/4 inch?
No, 5 mm (0.197 inches) is slightly less than 1/4 inch (0.250 inches = 6.35 mm). The difference is about 1.35 mm. To get exactly 1/4 inch, you need 6.35 mm. In fractional inch terms, 5 mm is closer to 3/16 inch (4.7625 mm) than to 1/4 inch (6.35 mm).
How do I convert mm to fractional inches?
First, divide the mm value by 25.4 to get decimal inches. Then convert the decimal to the nearest standard fraction. For example: 6 mm ÷ 25.4 = 0.2362 inches, which is closest to 15/64 inch or approximately 1/4 inch. Common fractions used in imperial measurements are 1/32, 1/16, 3/32, 1/8, 5/32, 3/16, 7/32, 1/4, 5/16, 3/8, 7/16, 1/2, and so on. Our converter shows the nearest fractional inch automatically.
What is the difference between mm, cm, and inches?
1 centimeter (cm) = 10 millimeters (mm). 1 inch = 25.4 mm = 2.54 cm. Millimeters are the smallest of these three units and provide the most precision for small measurements. Use mm for engineering, jewelry, and precision work. Use cm for general metric measurements. Use inches for imperial-system construction, woodworking, and US-standard measurements.
How many mm is 12 inches (1 foot)?
12 inches (1 foot) equals exactly 304.8 millimeters. The calculation is 12 × 25.4 = 304.8 mm. This is also equal to 30.48 centimeters. A standard 12-inch (1-foot) ruler is therefore 304.8 mm long in metric terms.
Is 20 mm the same as 1 inch?
No, 20 mm is not the same as 1 inch. 20 mm equals 0.787 inches, which is about 25/32 of an inch. To equal 1 inch, you need exactly 25.4 mm. The difference between 20 mm and 1 inch is 5.4 mm — a significant gap in precision work. 20 mm is commonly used for watch band widths and coin diameters.
What common objects are measured in mm?
Many everyday items use millimeter measurements: jewelry (ring bands 2-6 mm, gemstones 4-10 mm), bolts and screws (M3 = 3 mm, M6 = 6 mm, M8 = 8 mm diameter), camera lenses (35 mm, 50 mm, 85 mm focal length), phone thickness (7-9 mm), bullet calibers (9 mm), wrench and socket sizes, SIM card dimensions, and screen bezels.
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