Instant · Precise · Universal
23 units available
6 categories total
To convert barns to m²: multiply by 10⁻²⁸. To fm²: multiply by 100.
1 b = 10⁻²⁸ m² = 100 fm². Millibarns (mb), microbarns (µb), and nanobarns (nb) are common submultiples.
For example, 1 Barn (b) = 3.861006e-35 Square Mile (US Survey) (mi² (US)).
| Barn (b) | Square Mile (US Survey) (mi² (US)) |
|---|---|
| 0.1 | 3.861006e-36 |
| 0.5 | 1.930503e-35 |
| 1 | 3.861006e-35 |
| 2 | 7.722012e-35 |
| 5 | 1.930503e-34 |
| 10 | 3.861006e-34 |
| 25 | 9.652515e-34 |
| 50 | 1.930503e-33 |
| 100 | 3.861006e-33 |
| 500 | 1.930503e-32 |
| 1000 | 3.861006e-32 |
The barn is a unit of area equal to 10⁻²⁸ m², used to express nuclear cross-sections — the effective target area of subatomic particles.
1 b = 10⁻²⁸ m² = 100 fm². Millibarns (mb), microbarns (µb), and nanobarns (nb) are common submultiples.
To convert barns to m²: multiply by 10⁻²⁸. To fm²: multiply by 100.
Quantifying nuclear reaction probabilities, neutron absorption, and particle scattering in reactor design.
The physicists named it 'barn' as a joke: nuclei were 'as big as a barn' compared to what they expected. Later units include 'outhouse' (10⁻⁶ barns) and 'shed' (10⁻²⁴ barns).
Thinking a barn is a large area — at the human scale 10⁻²⁸ m² is incomprehensibly small.
Cross-section = probability of interaction. A bigger barn value means a particle is more likely to 'hit the target' — hence the barn analogy.
The US survey square mile is a historical area unit based on the US survey foot, equal to approximately 2,589,998.47 m².
1 mi² (US) ≈ 2,589,998.47 m². Differs from international mi² (2,589,988.11 m²) by about 10.36 m².
To convert US survey mi² to km²: multiply by 2.590. To international mi²: multiply by ~1.000004.
Historical US Public Land Survey System sections (each nominally 1 mi² US survey).
Over one square mile, the US survey definition differs from the international definition by about 10.4 m² — roughly a 3 m × 3.5 m room.
Using the US survey mile for new calculations. Deprecated since 2023 — use the international definitions.
The US Survey system was a legacy from 1893. Its 2023 retirement unified US measurements with the international standard.



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