Convert Inch (in) to Millimeter (mm) instantly. Enter any value and get the result immediately.
in → mm Converter
| Inch (in) | Millimeter (mm) |
|---|---|
| 0.1 in | 2.54 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
| 200 in | 5080 mm |
| 500 in | 12,700 mm |
| 1000 in | 25,400 mm |
| 5000 in | 127,000 mm |
| 10000 in | 254,000 mm |
Converting inches to millimeters is one of the most practical and frequently performed cross-system unit conversions in engineering, manufacturing, and everyday life. Inches are the standard for measurements in the United States, while millimeters are the preferred unit for precise technical work worldwide — used on engineering drawings, in woodworking, and across international product specifications. Since one inch equals exactly 25.4 millimeters by international definition, the conversion is simple: multiply the inch value by 25.4. Use the converter above for instant results, or follow the formula and examples below.
Step-by-step example — Convert 6 in to millimeters:
Step-by-step example — Convert 3.5 in to millimeters:
Inch (in) is an imperial and US customary unit of length equal to exactly 1/12 of a foot or 2.54 centimeters, established by international agreement in 1959. The inch is the everyday standard for screen and display sizes (TVs, monitors, smartphones), pipe and tube diameters in US plumbing and HVAC, tire and wheel rim widths, fastener sizes, and component dimensions across US hardware, electronics, and manufacturing. Alongside feet, it is also the unit used for human height in the United States. One inch is approximately the width of an adult thumb at the knuckle — a familiar, intuitive unit for fine-scale measurements in daily American and British life.
Millimeter (mm) is a metric unit of length equal to one-thousandth of a meter (10⁻³ m) or one-tenth of a centimeter. The prefix "milli-" means one-thousandth in the SI system. Millimeters are the dominant unit for precise technical measurements in engineering drawings (following ISO and DIN standards), woodworking and furniture dimensions, CNC machine programming, medical device specifications, and consumer product dimensions internationally. Familiar references include the thickness of a credit card (0.76 mm), the diameter of a standard pencil (7 mm), a 35mm film frame width, and common drill bit sizes in metric sets. One inch equals exactly 25.4 millimeters — a clean, internationally fixed value.
| Inches (in) | Millimeters (mm) | Common Reference |
|---|---|---|
| 1/16 in (0.0625) | 1.5875 mm | Smallest common US ruler graduation |
| 1/8 in (0.125) | 3.175 mm | Common small drill bit size |
| 1/4 in (0.25) | 6.35 mm | Standard audio jack diameter |
| 1/2 in (0.5) | 12.7 mm | Half inch / common pipe size |
| 1 in | 25.4 mm | One inch exactly |
| 2 in | 50.8 mm | Standard PVC pipe diameter (nominal) |
| 3.5 in | 88.9 mm | Standard 2×4 lumber actual width |
| 6 in | 152.4 mm | Half a foot / standard ruler half-length |
| 8 in | 203.2 mm | Standard chef's knife blade length (approx.) |
| 12 in | 304.8 mm | One foot / standard ruler length |
There are exactly 25.4 millimeters in one inch. This is a fixed, internationally defined value established by the 1959 International Yard and Pound Agreement: 1 in = 25.4 mm precisely.
The formula is: mm = in × 25.4. Multiply any inch value by 25.4 to get the exact equivalent length in millimeters.
1 in = 25.4 mm exactly. This is one of the most important and widely used unit conversion values in engineering, manufacturing, and international trade — memorizing "1 inch = 25.4 mm" is a practical skill for anyone working across both measurement systems.
1 mm = 0.03937 in (approximately 1/25.4 inches). One millimeter is just under four-hundredths of an inch — roughly the thickness of a credit card or a standard paperclip wire diameter.
An inch is larger than a millimeter. One inch equals exactly 25.4 millimeters — making an inch about twenty-five times the length of a single millimeter. In practical terms, an inch is a coarser unit used for overall dimensions, while millimeters provide the finer precision needed for detailed engineering specifications and tolerance work.
The exact relationship of 1 inch = 25.4 mm was established by the International Yard and Pound Agreement of 1959, signed by the United States, the United Kingdom, Canada, Australia, New Zealand, and South Africa. Before this agreement, slightly different national standards for the inch existed. The value of 25.4 mm was chosen as the best reconciliation of the existing US and UK inch definitions, and it has been the legally exact definition of the international inch ever since — making the in-to-mm conversion perfectly precise with no rounding required.
The simplest mental shortcut is to multiply by 25, then add 1.6% of the original inch value. For example, 4 inches: 4 × 25 = 100, plus 4 × 0.4 = 1.6, giving approximately 101.6 mm (exact: 4 × 25.4 = 101.6 mm — perfect). Alternatively, many engineers simply memorize a few key benchmarks: ½ in = 12.7 mm, 1 in = 25.4 mm, 2 in = 50.8 mm, and scale from there. For everyday estimates, treating 1 inch as "about 25 mm" gives a quick result within 2% accuracy.