A barn is a nuclear cross-section unit equal to 1e-28 square meters.
Barns to Square Megameters Converter — b to Mm2
Convert Barn (b) to Square Megameter (Mm2) using the exact conversion factor (1 barn = 1e-40 square megameter). See the formula, worked examples, and conversion table.
Barns to Square Megameters 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+12.
Area uses the square meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Barns to Square Megameters
Comparing Barn and Square Megameter 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 megameters = barns × 1e-40
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 megameter equals 1e+12 base units, so dividing one by the other gives the direct barn-to-square megameter factor of 1e-40.
Simple example
1 b × 1e-40 = 1e-40 Mm2
1 barn = 1e-40 square megameters.
Real-world example
10 b × 1e-40 = 1e-39 Mm2
10 barns = 1e-39 square megameters.
Conversion table
| Barn (b) | Square Megameter (Mm2) |
|---|---|
| 1 b | 1e-40 Mm2 |
| 5 b | 5e-40 Mm2 |
| 10 b | 1e-39 Mm2 |
| 25 b | 2.5e-39 Mm2 |
| 50 b | 5e-39 Mm2 |
| 100 b | 1e-38 Mm2 |
Reverse conversion: Square Megameter to Barn
1e-40 Mm2 × 1e+40 = 1 b
1e-40 square megameters = 1 barn.
barns = square megameters × 1e+40
For a page dedicated to this direction, see Square Megameter to Barn.
Understanding the Barn (b)
A barn is a nuclear cross-section unit equal to 1e-28 square meters.
Understanding the Square Megameter (Mm2)
Square metric area unit.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many square megameters are in 1 barn?
1 barn equals 1e-40 square megameters, using the exact defined conversion factor rather than an estimate.
How do I convert barn to square megameter?
Multiply the barn value by 1e-40. The converter above does this instantly to whatever precision you set.
How do I convert square megameter back to barn?
Use the reverse factor: 1 square megameter equals 1e+40 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 megameter?
Square Megameter (Mm2) is a unit of area.
Is the barn to square megameter conversion exact?
Yes. Both barn and square megameter are defined by fixed standards rather than physical artifacts, so the factor of 1e-40 used above is exact to as many digits as you choose to display.