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'.
1 barn = 1×10⁻²⁸ square meters (exactly).
About the 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.
Sources: Wikipedia: Barn (unit); NIST SP 811, Appendix B.8 conversion factors
Barn conversion chart
1 barn expressed in every other area unit:
| Unit | 1 barn |
|---|---|
| Square Meters | 1×10⁻²⁸ |
| Square Kilometers | 1×10⁻³⁴ |
| Hectares | 1×10⁻³² |
| Square Inches | 1.5500031×10⁻²⁵ |
| Square Feet | 1.076391042×10⁻²⁷ |
| Square Yards | 1.195990046×10⁻²⁸ |
| Acres | 2.471053815×10⁻³² |
| Square Miles | 3.861021585×10⁻³⁵ |
| Square Centimeters | 1×10⁻²⁴ |
| Square Millimeters | 1×10⁻²² |
| Tsubo | 3.025×10⁻²⁹ |
| Pyeong | 3.025×10⁻²⁹ |
| Rai (Thai) | 6.25×10⁻³² |
| Ares | 1×10⁻³⁰ |
| Square Rods | 3.953686103×10⁻³⁰ |
| Square Chains | 2.471053815×10⁻³¹ |
| Roods | 9.884215259×10⁻³² |
| Oxgangs | 1.64736921×10⁻³³ |
| Virgates | 8.236846049×10⁻³⁴ |
| Hides | 2.059211512×10⁻³⁴ |
| US Survey Acres | 2.47104393×10⁻³² |
| Sections | 3.861006141×10⁻³⁵ |
| Townships | 1.072501706×10⁻³⁶ |
| Iugera | 3.963000162×10⁻³² |
| Jō (tatami Mat) | 6.05×10⁻²⁹ |
| Se | 1.008333333×10⁻³⁰ |
| Tan | 1.008333333×10⁻³¹ |
| Chō (area) | 1.008333333×10⁻³² |
| Mu (Chinese) | 1.5×10⁻³¹ |
| Qing (Chinese) | 1.5×10⁻³³ |
| Ngan (Thai) | 2.5×10⁻³¹ |
| Square Wa (Thai) | 2.5×10⁻²⁹ |
| Guntha | 9.884215259×10⁻³¹ |
| Cents (India) | 2.471053815×10⁻³⁰ |
| Marlas | 3.953686103×10⁻³⁰ |
| Kanals | 1.976843052×10⁻³¹ |
| Dunams | 1×10⁻³¹ |
| Feddans | 2.380952381×10⁻³² |
| Arpents | 2.924925926×10⁻³² |
More Scientific units
- femtometer (length)
- angstrom (length)
- dalton (weight & mass)
- cubic kilometer (volume)
- degree Rankine (temperature)
- degree Newton (temperature)
- picosecond (time)
- shake (time)
- Mach (speed)
- speed of light (speed)
- kilometer per second (speed)
- calorie (energy)
- kilocalorie (energy)
- electronvolt (energy)
- kiloelectronvolt (energy)
- megaelectronvolt (energy)
Browse all area units.