12 in = 304.8 mm (inch → millimeter)
12 in = 304.8 mm
12 inches (in) equals 304.8 millimeters (mm). The conversion uses the exact factor 25.4: 12 × 25.4 = 304.8.
Millimeters = Inches × 25.4How 12 inches compares to its arithmetic neighbours, converted to millimeters.
| Relation | inches | millimeters |
|---|---|---|
| ÷10 | 1.2 in | 30.48 mm |
| ÷2 (half) | 6 in | 152.4 mm |
| ×1 (this value) | 12 in | 304.8 mm |
| ×2 (double) | 24 in | 609.6 mm |
| ×5 | 60 in | 1524 mm |
| ×10 | 120 in | 3048 mm |
Inches to millimetres multiplies by 25.4 exactly. A 1/2 in pipe is 12.7 mm; a 1/4-20 UNC machine screw is 6.35 mm in major diameter. The factor is by definition (1959 international yard and pound agreement), so the conversion is lossless to any precision your input justifies. Watch for fractional inches: 3/8 in is 9.525 mm, not 9.5 mm — the half-millimetre matters when matching a metric drill bit to an imperial hole.
Gunsmiths chambering a rifle barrel work from a bore diameter spec given in inches by American manufacturers but the reamers and gauge pins used for the actual machining are frequently metric, sold in millimetre increments. A 0.308 in bore is 7.82 mm, distinct from the common 7.62 mm metric bore size by a small but load-bearing 0.2 mm — using the wrong reamer at this tolerance level ruins the barrel. Convert to four decimal places minimum; bore work has essentially no margin for rounding.
Start with your value in inches.
Multiply the inch value by 25.4. This is the exact conversion factor from inches to millimeters.
The product is your value in millimeters. For example, 5 in × 25.4 = 127 mm.
The exact factor from inches to millimeters is 25.4.
Millimeters = Inches × 25.4
Fifty common reference values, hand-picked for skim utility. Use the calculator above for any value not listed.
| Inches (in) | Millimeters (mm) |
|---|---|
| 0.1 in | 2.54 mm |
| 0.25 in | 6.35 mm |
| 0.5 in | 12.7 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 4 in | 101.6 mm |
| 5 in | 127 mm |
| 6 in | 152.4 mm |
| 7 in | 177.8 mm |
| 8 in | 203.2 mm |
| 9 in | 228.6 mm |
| 10 in | 254 mm |
| 11 in | 279.4 mm |
| 12 in | 304.8 mm |
| 13 in | 330.2 mm |
| 14 in | 355.6 mm |
| 15 in | 381 mm |
| 16 in | 406.4 mm |
| 18 in | 457.2 mm |
| 20 in | 508 mm |
| 22 in | 558.8 mm |
| 24 in | 609.6 mm |
| 25 in | 635 mm |
| 28 in | 711.2 mm |
| 30 in | 762 mm |
| 32 in | 812.8 mm |
| 36 in | 914.4 mm |
| 40 in | 1016 mm |
| 45 in | 1143 mm |
| 48 in | 1219.2 mm |
| 50 in | 1270 mm |
| 60 in | 1524 mm |
| 70 in | 1778 mm |
| 75 in | 1905 mm |
| 80 in | 2032 mm |
| 90 in | 2286 mm |
| 100 in | 2540 mm |
| 125 in | 3175 mm |
| 150 in | 3810 mm |
| 200 in | 5080 mm |
| 250 in | 6350 mm |
| 300 in | 7620 mm |
| 400 in | 10160 mm |
| 500 in | 12700 mm |
| 600 in | 15240 mm |
| 750 in | 19050 mm |
| 800 in | 20320 mm |
| 900 in | 22860 mm |
| 1000 in | 25400 mm |
A US quarter coin is about 1 inch in diameter. A standard sheet of US Letter paper is 8.5 × 11 inches. A 13-inch laptop has a screen diagonal of 13 inches. In millimeters, that gives you: 1 in = 25.4 mm, 10 in = 254 mm, 100 in = 2540 mm.
The inch (in) is a unit of length in the imperial and US customary systems, defined as exactly 25.4 millimeters since the 1959 international yard and pound agreement. It is the standard unit in the US for screen sizes, lumber, fasteners, and personal height when given in feet-and-inches form. Twelve inches make one foot.
The millimeter (mm) is a metric unit of length equal to one-thousandth of a meter. It is the working unit of engineering drawings, precision manufacturing, electronics, and most consumer-goods specifications outside the United States. A credit card is about 0.76 mm thick; the diameter of a pencil lead is around 2 mm.
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