Barns to Square Meters Converter
Convert the nuclear/particle-physics area unit “barn” and its submultiples to square meters. Also works in reverse (m² → barn) for cross sections.
1 b = 1 × 10⁻²⁸ m² (exact by definition)
Results
Handy for HEP data: experiments often quote pb or fb.
Conversion formula
1 b = 1 × 10⁻²⁸ m²
m² = barns × 1 × 10⁻²⁸
barns = m² ÷ 1 × 10⁻²⁸
1 pb = 10⁻¹² b, 1 fb = 10⁻¹⁵ b
Because the barn is so tiny, results in square meters will look like 5e-28 or smaller — that’s expected.
Barns → m² reference table
| Barns (b) | Square meters (m²) | Picobarns (pb) |
|---|
All values are exact powers of 10; shown in scientific notation where convenient.
What is a barn?
The barn (symbol b) is a non-SI unit of area used in nuclear and particle physics to express cross-sectional areas of nuclei and particles. It was coined during the Manhattan Project, jokingly referring to a “barn door” — as in, “couldn’t hit the broad side of a barn,” even though the unit is extremely small.
Why use 10⁻²⁸ m²?
Typical nuclear cross sections are around the size of atomic nuclei, which makes square meters very inconvenient. Defining 1 barn = 10⁻²⁸ m² gives a number of order 1 for many interactions.
FAQ
1. Do we ever use larger units?
Yes, experiments often report in millibarns (mb), microbarns (μb), nanobarns (nb), picobarns (pb) or femtobarns (fb), depending on how rare the process is.
2. Can I convert square centimeters instead?
Convert barns → m² here, then m² → cm² using 1 m² = 10⁴ cm².
3. Are barns an SI unit?
No, but they are widely accepted in the high-energy physics community and well-documented.
Formula (LaTeX) + variables + units
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1 b = 1 × 10⁻²⁸ m² m² = barns × 1 × 10⁻²⁸ barns = m² ÷ 1 × 10⁻²⁸ 1 pb = 10⁻¹² b, 1 fb = 10⁻¹⁵ b
- No variables provided in audit spec.
- NIST — Weights and measures — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/weights-and-measures - NIST — SI units — nist.gov · Accessed 2026-01-19
https://www.nist.gov/pml/owm/metric-si/si-units
Last code update: 2026-01-19
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