A barn is a nuclear cross-section unit equal to 1e-28 square meters.
Barns to Square Millimeters Converter — b to mm2
Convert Barn (b) to Square Millimeter (mm2) using the exact conversion factor (1 barn = 1e-22 square millimeter). See the formula, worked examples, and conversion table.
Barns to Square Millimeters converter
Converter
Area Converter
Convert land, construction, mapping, survey, and scientific area units.
Context values
Some unit families need one extra value for a physically accurate result.
Square metric area unit.
Result = input x 1e-28 / 1e-6.
Area uses the square meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Barns to Square Millimeters
Comparing Barn and Square Millimeter is common in agriculture and real estate, where US land is typically measured in acres and most of the rest of the world uses hectares. Specifically: A barn is a nuclear cross-section unit equal to 1e-28 square meters, and square metric area unit.
Formula
square millimeters = barns × 1e-22
This factor comes from each unit's defined relationship to the category's base unit: 1 barn equals 1e-28 base units, and 1 square millimeter equals 0.000001 base units, so dividing one by the other gives the direct barn-to-square millimeter factor of 1e-22.
Simple example
1 b × 1e-22 = 1e-22 mm2
1 barn = 1e-22 square millimeters.
Real-world example
10 b × 1e-22 = 1e-21 mm2
10 barns = 1e-21 square millimeters.
Conversion table
| Barn (b) | Square Millimeter (mm2) |
|---|---|
| 1 b | 1e-22 mm2 |
| 5 b | 5e-22 mm2 |
| 10 b | 1e-21 mm2 |
| 25 b | 2.5e-21 mm2 |
| 50 b | 5e-21 mm2 |
| 100 b | 1e-20 mm2 |
Reverse conversion: Square Millimeter to Barn
1e-22 mm2 × 1e+22 = 1 b
1e-22 square millimeters = 1 barn.
barns = square millimeters × 1e+22
For a page dedicated to this direction, see Square Millimeter to Barn.
Understanding the Barn (b)
A barn is a nuclear cross-section unit equal to 1e-28 square meters.
Understanding the Square Millimeter (mm2)
Square metric area unit.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many square millimeters are in 1 barn?
1 barn equals 1e-22 square millimeters, using the exact defined conversion factor rather than an estimate.
How do I convert barn to square millimeter?
Multiply the barn value by 1e-22. The converter above does this instantly to whatever precision you set.
How do I convert square millimeter back to barn?
Use the reverse factor: 1 square millimeter equals 1e+22 barns. You can also use the swap control in the converter above to flip the direction instantly.
What is a barn?
Barn (b) is a unit of area.
What is a square millimeter?
Square Millimeter (mm2) is a unit of area.
Is the barn to square millimeter conversion exact?
Yes. Both barn and square millimeter are defined by fixed standards rather than physical artifacts, so the factor of 1e-22 used above is exact to as many digits as you choose to display.