Spans to Millimeters (span to mm)

1 span equals 228.6 millimeters exactly.

1 span = 228.6 millimeters

How to convert spans to millimeters

To convert spans to millimeters, multiply the number of spans by 228.6. This factor is exact. To go the other way, multiply millimeters by 0.004374453193 (rounded).

millimeters = spans × 228.6

Example: 10 spans = 2,286 millimeters.

About these units

Span (span)

Medieval EnglishHistorical unit (no longer in standard use)

9 inches (22.86 cm), the distance from the tip of the thumb to the tip of the little finger of a spread hand.

Stretch your fingers as wide as they go and the gap from thumb tip to little fingertip is a span. The English word descends from Old English spann and a Proto-Germanic form meaning handbreadth, itself tied to a root meaning to stretch. Greek writers had spithame, which appears in Herodotus in the 5th century BC, and Hesiod used a word meaning three spans long three centuries earlier. Ancient systems treated the span as half a cubit, or three palms.

The English handspan is 9 inches, or 22.86 cm, and Wiktionary notes it as an eighth of a fathom. That is the figure used here, though a hand's reach differs from person to person and other countries' spans differ too: about 23 cm for a Slovenian great span, 17.8 cm for the Russian piad, and 15 to 20 cm in Chinese usage. A little or short span, from thumb to index finger, was much smaller. The unit is now mostly a figure of speech, as in the span of a bridge or of a wing.

1 span = 0.2286 meters (exactly).

Sources: Wikipedia: Span (unit); Wiktionary: span

Millimeter (mm)

Metric (SI)Current unit

One thousandth of a meter. Used in engineering, manufacturing and rainfall measurement.

Carl Friedrich Gauss put the millimeter at the base of his 1832 proposal for absolute units, pairing it with the milligram and the second, although the centimeter-based CGS system later won out among scientists. The name combines the metric prefix milli-, from the Latin for one thousand, with the meter. Since 1983 a millimeter has been tied to the speed of light: it is the distance light covers in 1/299,792,458,000 of a second.

Millimeters are the language of fine mechanical work. Standard rulers are divided into them, digital calipers commonly read to 0.01 mm, and mechanical pencil leads come in 0.5 and 0.7 mm. Copy paper is about 0.1 mm thick, and a thin hair, at 0.02 to 0.04 mm across, is close to the smallest thing the naked eye can see. A wave with a frequency of 300 GHz has a wavelength of 1 mm. An inch is exactly 25.4 mm. One trap for readers in the United States is that mil there traditionally means a thousandth of an inch, not a millimeter.

1 millimeter = 0.001 meters (exactly).

Sources: Wikipedia: Millimetre; Wikipedia: Centimetre-gram-second system of units; NIST Guide to the SI, Appendix B.8: conversion factors

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