Inches
0
Converted length
Convert mm to inches — and inches to mm — instantly with precise results
Free bidirectional millimetres to inches converter with centimetre and foot equivalents. Full reference chart included for 2026.
Accurate metric to Imperial length conversion for engineering, construction, and everyday use
Convert millimetres to inches using the exact internationally defined ratio: 1 inch = 25.4 mm. Our converter delivers accurate results for any value — from fractions of a millimetre to thousands of millimetres — making it reliable for professional and everyday use.
Every conversion shows the result in inches, feet, centimetres, and metres simultaneously. This makes it easy to cross-reference metric and Imperial measurements without switching tools — all from a single input value.
Essential for engineering drawings, woodworking, screen sizes, tyre profiles, construction plans, and any task where metric and Imperial measurements must be compared. Widely used by tradespeople, designers, and students in 2026.
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The millimetre (mm) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre. The inch (in) is the base unit of length in the Imperial and US customary systems. The exact relationship between the two is defined internationally: 1 inch = 25.4 millimetres. This definition has been fixed since 1959 and is used as the basis for all metric-to-Imperial length conversions worldwide.
To convert millimetres to inches, divide the value by 25.4. To convert inches back to millimetres, multiply by 25.4. For example, 100 mm ÷ 25.4 = 3.937 inches. This conversion is widely used in engineering, manufacturing, and construction where metric drawings must be interpreted in Imperial units or vice versa. For other unit converters, see the BTU to joules converter.
1 inch = 25.4 mm exactly (internationally defined since 1959). All other conversions derive from this fixed relationship.
Converting millimetres to inches requires one simple division step. Whether you are reading an engineering drawing, measuring screen dimensions, or working on a woodworking project, the same formula applies every time.
In the Imperial system, inches are often expressed as fractions (e.g., 3/8", 5/16"). When converting mm to fractional inches, first convert to decimal inches, then find the nearest standard fraction. For example, 10 mm = 0.3937 in ≈ 25/64 inches. Engineering work typically uses decimal inches for precision.
Use this table for the most common mm to inches conversions. The desktop table includes centimetres, metres, and feet equivalents; on mobile use the card view below.
| Millimetres (mm) | Inches (in) | Centimetres (cm) | Feet (ft) | Fractional Inches |
|---|---|---|---|---|
| 1 mm | 0.03937 in | 0.1 cm | 0.00328 ft | ≈ 1/25 in |
| 2 mm | 0.07874 in | 0.2 cm | 0.00656 ft | ≈ 5/64 in |
| 5 mm | 0.19685 in | 0.5 cm | 0.01640 ft | ≈ 13/64 in |
| 10 mm | 0.39370 in | 1.0 cm | 0.03281 ft | ≈ 25/64 in |
| 12.7 mm | 0.5 in | 1.27 cm | 0.04167 ft | 1/2 in (exact) |
| 15 mm | 0.59055 in | 1.5 cm | 0.04921 ft | ≈ 19/32 in |
| 20 mm | 0.78740 in | 2.0 cm | 0.06562 ft | ≈ 25/32 in |
| 25 mm | 0.98425 in | 2.5 cm | 0.08202 ft | ≈ 63/64 in |
| 25.4 mm | 1.0 in | 2.54 cm | 0.08333 ft | 1 inch (exact) |
| 30 mm | 1.18110 in | 3.0 cm | 0.09843 ft | ≈ 1 3/16 in |
| 50 mm | 1.96850 in | 5.0 cm | 0.16404 ft | ≈ 1 31/32 in |
| 75 mm | 2.95276 in | 7.5 cm | 0.24606 ft | ≈ 2 61/64 in |
| 100 mm | 3.93701 in | 10.0 cm | 0.32808 ft | ≈ 3 15/16 in |
| 150 mm | 5.90551 in | 15.0 cm | 0.49213 ft | ≈ 5 29/32 in |
| 200 mm | 7.87402 in | 20.0 cm | 0.65617 ft | ≈ 7 7/8 in |
| 250 mm | 9.84252 in | 25.0 cm | 0.82021 ft | ≈ 9 27/32 in |
| 300 mm | 11.81102 in | 30.0 cm | 0.98425 ft | ≈ 11 13/16 in |
| 500 mm | 19.68504 in | 50.0 cm | 1.64042 ft | ≈ 19 11/16 in |
| 1000 mm | 39.37008 in | 100.0 cm | 3.28084 ft | ≈ 39 3/8 in |
One inch is defined as exactly 25.4 millimetres. This has been the international standard since 1959, agreed upon by the UK, USA, Australia, Canada, New Zealand, and South Africa. It is exact — no rounding — making all mm/inch conversions perfectly precise.
To convert mm to inches, multiply by 0.03937008 (which equals 1 ÷ 25.4). For example, 75 mm × 0.03937 = 2.9528 inches. This factor is commonly used in engineering software, spreadsheets, and CAD applications for metric-to-Imperial conversions.
Screen sizes are measured diagonally in inches in most markets. A 27-inch monitor diagonal equals 685.8 mm (27 × 25.4). Pixel density (PPI) is also calculated using the inch, making mm-to-inch conversions essential for display technology and graphic design work.
In precision engineering and CNC machining, tolerances are often specified in either mm or thousandths of an inch (thou). One thou = 0.001 in = 0.0254 mm. Converting between these tiny units accurately is critical for manufacturing quality control in 2026.
Timber and construction materials are often sold in Imperial sizes (e.g., 2×4 lumber) but measured and cut in metric in many countries. A standard 2×4 is actually 38 mm × 89 mm in real dimensions — highlighting the daily need for mm-to-inch conversion in trades.
Vehicle tyre sizes use a mixed system: the tyre width is in mm, but the wheel diameter is in inches. A 225/45 R17 tyre has a 225 mm width and fits a 17-inch (431.8 mm) wheel. Converting between the two systems is essential for tyre fitting and automotive applications.
The mm to inches conversion is one of the most frequently needed length conversions in technical and everyday work. It bridges the metric system used in science and most countries with the Imperial system still dominant in the USA and widely used in the UK, Australia, and Canada.
The metric system uses millimetres, centimetres, and metres, while the Imperial system uses inches, feet, and yards. Since 1 inch = 25.4 mm exactly, all metric-Imperial length conversions derive from this single defined constant.
Area Converter →ISO standards use metric units (mm) while ANSI/ASME standards often use inches. Engineers working across both systems rely daily on precise mm-to-inch conversion to ensure dimensional accuracy in designs, tolerances, and manufacturing specifications.
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