Barns to Square Meters (b to m²)
1 barn equals 1×10⁻²⁸ square meters exactly.
How to convert barns to square meters
To convert barns to square meters, multiply the number of barns by 1×10⁻²⁸. This factor is exact. To go the other way, multiply square meters by 1×10²⁸.
square meters = barns × 1×10⁻²⁸
Example: 10 barns = 1×10⁻²⁷ square meters.
About these units
Barn (b)
Exactly 10⁻²⁸ square meters. Used in nuclear and particle physics for reaction cross-sections; the name is a joke about a target 'as big as a barn'.
Nuclear physicists coined this unit during the Second World War. Marshall Holloway and Charles Baker, working at Purdue on Manhattan Project problems, wanted a short name for the cross section of a nucleus and passed over names such as Oppenheimer and Bethe. They settled on a joke about a target that was really as big as a barn, and the word first appeared in print in a secret Los Alamos report of June 1943.
One barn is 10 to the power of minus 28 square meters, or 100 square femtometers, roughly the cross-sectional area of a uranium nucleus. NIST lists the conversion as exact. The barn was never an SI unit, though the BIPM acknowledged it in the eighth SI Brochure because particle physics relies on it. Prefixed forms dominate today: the femtobarn is the usual choice in high-energy physics, and the inverse femtobarn measures integrated luminosity. Informal names exist too, such as outhouse for a microbarn and shed for a yoctobarn.
1 barn = 1×10⁻²⁸ square meters (exactly).
Sources: Wikipedia: Barn (unit); NIST SP 811, Appendix B.8 conversion factors
Square Meter (m²)
The SI unit of area: a square one meter on each side. Used for floor areas and property sizes in most of the world.
Squaring the meter was built into the metric system from the start. The French law of 18 Germinal, Year III (7 April 1795) defined the are, the land unit that gave the hectare its name, as exactly 100 square meters, so the square meter was already the foundation of metric land measure. Nobody is credited with inventing it as a separate unit. It is simply the area of a square one meter on each side, and any SI prefix that works for the meter works for it, with the prefix squared along with the unit.
That squaring catches people out: a square kilometer is one million square meters, not one thousand. Since 1983 the meter has been defined through the speed of light, so the square meter is tied to a constant of nature as well as to the second. A hectare, about the area of Trafalgar Square in London, is 10,000 square meters. In everyday terms one square meter is about 10.76 square feet. Unicode has a compatibility character for it, but the recommended way to write it is the plain superscript two: m².
The square meter is the reference unit for area on this site.
Sources: Wikipedia: Square metre; Wikipedia: Are (unit); NIST: the meter and the SI redefinition
Related conversions
- Square meters to barns (reverse)
- Barns to square kilometers
- Barns to hectares
- Barns to square inches
- Barns to square feet
- Barns to square yards
- Barns to acres
- Barns to square miles
- Square kilometers to square meters
- Hectares to square meters
- Square inches to square meters
- Square feet to square meters
- Square yards to square meters
- Acres to square meters
- Square miles to square meters
- Square centimeters to square meters
- Square millimeters to square meters
- Tsubo to square meters
- Pyeong to square meters
- Rai (Thai) to square meters
See all area units.