Inch
Definition: An inch (symbol: in) measures length in the imperial and US customary systems. Since 1959, it equals exactly 25.4 millimeters. A foot has 12 inches, and a yard has 36 inches.
History/origin: The word “inch” comes from the Latin “uncia,” meaning one-twelfth of a Roman foot.
Old standards varied, but today’s inch links to the international yard. Early on, people used three dry, round barley grains laid end-to-end as one inch. Another idea tied it to human thumbs—averaging widths from small, medium, and large ones.
Current use: The inch is common in the United States, Canada, and the United Kingdom. Japan and other places use it for electronic parts, like screen sizes.
Millimeter
Definition: A millimeter (mm) measures length in the world’s standard system (SI). It equals 1/1000 of a meter. That’s the distance light travels in 1/299,792,458,000 of a second.
History/origin: The “milli-” part means one-thousandth. It comes from many metric prefixes and applies to the meter here. The meter’s definition has changed over time. Now, it uses the speed of light over a set time. But the link between meter and millimeter stays the same. Before, the meter came from a metal bar prototype. In 2019, experts updated it based on a new second definition.
Current use: People mainly use millimeter in the United States, Canada, and the United Kingdom. Japan and some other countries use it for electronic parts, like screen sizes.
Inch to Millimeter Conversion Table
| Inch [in] | Millimeter [mm] |
| 0.01 in | 0.254 mm |
| 0.1 in | 2.54 mm |
| 1 in | 25.4 mm |
| 2 in | 50.8 mm |
| 3 in | 76.2 mm |
| 5 in | 127 mm |
| 10 in | 254 mm |
| 20 in | 508 mm |
| 50 in | 1270 mm |
| 100 in | 2540 mm |
| 1000 in | 25400 mm |
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1 in = 25.4 mm
1 mm = 0.0393700787 in
Example: convert 15 in to mm:
15 in = 15 × 25.4 mm = 381 mm
1 inch is exactly 25.4 millimeters (mm). That’s the standard inch to mm conversion.
3 inches is 76.2 mm. Multiply 3 by 25.4 for fast inch to mm math.
Multiply inches by 25.4 to get mm. For example, 2 inches times 25.4 equals 50.8 mm. Use this easy inch to mm formula every time.
1/8 inch is 3.175 mm. It’s a small size, like the thickness of a paperclip wire.
No, 40 mm is about 1.57 inches. It’s bigger than 1 inch (which is 25.4 mm).
A pulgada is the Spanish word for “inch.” It’s the same size: 25.4 mm.
No, 30 mm is about 1.18 inches. Close but a bit more than 1 inch.
Yes, 72 inches equals exactly 6 feet. There are 12 inches in 1 foot.
3 feet is 36 inches. Multiply feet by 12 to convert.
No, 20 mm is about 0.79 inches. It’s smaller than 1 inch.
“Inch” comes from an old English word for “thumb.” It was once the width of a man’s thumb, about 25.4 mm.
2 inches is 50.8 mm. Double 25.4 for this quick inch to mm conversion.
No, 32 mm is about 1.26 inches. A true inch is 25.4 mm.
1 mm is thicker. It’s bigger than 0.8 mm by 0.2 mm.
No, 13 mm is about 0.51 inches. Half an inch size.
Almost—25 mm is 0.98 inches. Very close to 1 inch (25.4 mm).
6 mm is a tiny bit more than 1/4 inch. On a ruler, it’s about the width of a pencil lead.
4 inches is 101.6 mm. Multiply 4 by 25.4 for exact inch to mm results.
No, 30 mm equals 1.18 inches. Not the same as 1 inch.
Yes—round 1 inch to 25 mm. It’s off by just 0.4 mm, great for fast estimates.
It’s from an old standard set in 1959. World rulers agreed 1 inch = 25.4 mm exactly for science and trade.
No, 22 mm is about 0.87 inches. Smaller than 1 inch.
6 inches is 152.4 mm. Use 6 times 25.4 for precise inch to mm conversion.
No, 1 inch is 2.54 cm. Much smaller than 12 cm.
No, 32 mm is 1.26 inches. Bigger than 1 inch.
Yes, pulgada means inch in Spanish. Same exact size: 25.4 mm.
No, 1 inch is 2.54 cm. Close to 3 cm but smaller.
Almost—1 inch is 25.4 mm. 25 mm is 0.98 inches.
No, 10 cm is about 3.94 inches. Much bigger than 1 inch.
16 mm is about 0.63 inches. Like the width of a ladybug or small watch band.
4 mm is 0.157 inches. Very thin, like a guitar string.
22 mm equals 0.87 inches. Common for watch bands or small bolts.
15 inches is 381 mm. Multiply 15 by 25.4 for this inch to mm conversion.