Femtometers to Inches (fm to in)

1 femtometer equals 3.937007874×10⁻¹⁴ inches (rounded).

1 femtometer = 3.937007874×10⁻¹⁴ inches

How to convert femtometers to inches

To convert femtometers to inches, multiply the number of femtometers by 3.937007874×10⁻¹⁴. The factor is rounded to 10 significant digits. To go the other way, multiply inches by 25,400,000,000,000.

inches = femtometers × 3.937007874×10⁻¹⁴

Example: 10 femtometers = 3.937007874×10⁻¹³ inches.

About these units

Femtometer (fm)

ScientificCurrent unit

One quadrillionth of a meter, also called a fermi. The scale of atomic nuclei; a proton is roughly 0.84 fm in radius.

Robert Hofstadter coined the nickname fermi for this length in a 1956 paper in Reviews of Modern Physics, honoring Enrico Fermi. The formal name comes from femto, which Wikipedia traces to the Danish and Norwegian word femten, meaning fifteen, a nod to the factor of 10 to the minus 15. The prefix entered the SI in 1964, and Hofstadter also used the term in his 1961 Nobel Lecture.

One femtometer is a quadrillionth of a meter, or 1,000 picometers. The unit suits atomic nuclei: Wikipedia gives a proton charge radius of about 0.841 fm and a gold nucleus radius of about 8.45 fm, so a heavy nucleus is roughly ten times wider than a proton. The 0.841 fm figure from that article is the one used here. Cross-sections in the same field are measured in barns, and one barn equals 100 square femtometers.

1 femtometer = 1×10⁻¹⁵ meters (exactly).

Sources: Wikipedia: Femtometre; Wikipedia: Metric prefix; NIST: metric (SI) prefixes

Inch (in)

US & ImperialCurrent unit

1/12 of a foot. Defined as exactly 25.4 millimeters since 1959, when the US and Commonwealth countries agreed a common international inch.

Latin uncia, meaning one-twelfth, is the root of both inch and ounce, and it passed into Old English as ynce. Roman measurers divided their foot into twelve unciae, and the English inch kept that twelfth. After 1066 an inch was reckoned as three barleycorns, and a 1324 statute attributed to Edward II spelled out the definition as three grains of barley, dry and round, placed end to end lengthwise. For centuries the inch was simply a twelfth of a foot, or a thirty-sixth of a yard, and the US and UK each kept their own copy of the standard yard.

Those copies differed slightly until the 1959 international agreement fixed the yard at exactly 0.9144 meter, which made the inch exactly 25.4 millimeters. The US adopted it in 1959 and the UK ratified it in 1963, effective 1964. Today the inch is still the customary unit in the United States and Canada, and the UK keeps it on road signs. Worldwide it also names display diagonals, wheel rims, tire codes and pipe sizes.

1 inch = 0.0254 meters (exactly).

Sources: Wikipedia: Inch; Wikipedia: Yard; NIST Guide to the SI, Appendix B.8: conversion factors

Related conversions

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