Length · Unit Converter

Convert Barn to Square Kilometer

Convert barns to square kilometers instantly. 1 barn = 1e-34 square kilometer — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Square Kilometer to Barn converter for the reverse conversion.

Written by Sunith Babu L, Ph.D., Lead Engineer Reviewed by Girish V Kulkarni Ph.D.

Length category 2 min read Published June 6, 2026 Last reviewed June 6, 2026 Updated June 6, 2026

Units explained

Scientific / Physics

Barn

What is a barn?

A barn is a scientific unit of area equal to exactly 10⁻²⁸ m² (100 fm²). It is used in nuclear and particle physics to express interaction cross-sections.

Origin of the barn

Named in 1942 at Purdue University by physicists working on the Manhattan Project. The name comes from the phrase 'big as a barn' — uranium nuclei have cross-sections this large, which physicists initially considered surprisingly large for nuclear targets.

Where it is used

Barns and their submultiples (millibarn, microbarn, nanobarn, picobarn, femtobarn) are the standard units for cross-section measurements in nuclear physics, high-energy physics, and accelerator experiments. The Higgs boson production cross-section at the LHC is in the picobarn range.

When and where it was developed

Named in 1942 during the Manhattan Project; adopted internationally in particle physics.

Metric / SI

Square Kilometer

What is a square kilometer?

A square kilometer is a metric unit of area equal to 1,000,000 m² (one million square meters), or 100 hectares. It is used for measuring large land areas, regional geography, and country-scale statistics.

Origin of the square kilometer

Derived by squaring the kilometer (1000 m). The kilo- prefix comes from the Greek 'chilioi' (thousand).

Where it is used

Square kilometers express the area of cities, districts, lakes, forests, and entire countries. India's total area is approximately 3,287,263 km². 1 km² equals 100 hectares or about 247.105 acres.

When and where it was developed

Kilometer has been part of the metric system since 1795.

Barn to Square Kilometer conversion formula

The relationship between barns and square kilometers:

1 b = 1e-34 km²

1 km² = 1e+34 b

To convert barns to square kilometers, multiply the value in barns by 1e-34. To reverse, multiply square kilometers by 1e+34.

How to use this converter

Type a value into the calculator. The result in square kilometers updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Square Kilometer to Barn converter for the reverse direction.

Step-by-step: convert barns to square kilometers

Write down the value in barns (b).
Multiply that value by the factor 1e-34.
The product is the equivalent value in square kilometers (km²).
To reverse, multiply the square kilometer value by 1e+34.

Worked examples

Example 1 — Convert 1 b to km²:
1 × 1e-34 = 1e-34 km²

Example 2 — Convert 100 b to km²:
100 × 1e-34 = 1e-32 km²

Real-world example — Molecular dimensions

The diameter of small molecular structures (around 2 barns) is often converted into related sub-micron units when comparing measurements across different microscopy techniques or imaging modalities.

2 b × 1e-34 = 2e-34 km²

Real-world example — Wavelengths across the spectrum

Optical and atomic-scale phenomena are routinely cross-converted between sub-micron units. A photon of wavelength 800 barns can be re-expressed in square kilometers for direct comparison with another instrument's calibration data sheet.

800 b × 1e-34 = 8e-32 km²

Barn to Square Kilometer conversion table

Standard reference values for converting barns to square kilometers:

Barn [b]	Square Kilometer [km²]
0.01	1e-36
0.1	1e-35
1	1e-34
2	2e-34
3	3e-34
4	4e-34
5	5e-34
10	1e-33
20	2e-33
30	3e-33
40	4e-33
50	5e-33
100	1e-32
500	5e-32
1000	1e-31

Frequently asked questions

How many square kilometers is 1 barn?

1 barn equals 1e-34 square kilometer.

How do I convert barns to square kilometers?

Multiply the value in barns by 1e-34 to get square kilometers.

How do I convert square kilometers back to barns?

Multiply the value in square kilometers by 1e+34, or use the Square Kilometer to Barn converter.

How many square kilometers is 100 barns?

100 barns equals 1e-32 square kilometers, because 100 × 1e-34 = 1e-32.

Popular area unit conversions

ac → ft² m² → ft² ha → ac bigha → ft² ft² → m² ac → ha guntha → ft² ct → ft² ac → m² cm² → in² m² → ac km² → mi²

Convert Barn to other area units

Show all Barn conversions

Metric / SI (5 units)

Barn to Square Millimeter (mm²) Barn to Square Centimeter (cm²) Barn to Square Meter (m²) Barn to Hectare (ha) Barn to Square Kilometer (km²)

Imperial / US Customary (3 units)

Barn to Square Inch (in²) Barn to Square Foot (ft²) Barn to Acre (ac)

Scientific / Physics (4 units)

Barn to Shed (shed) Barn to Microbarn (µb) Barn to Outhouse (outh) Barn to Millibarn (mb)

Sources & references

Conversion factor (1 b = 1e-34 km²) verified against the following authoritative sources:

BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.

Results are provided for general reference. Verify critical measurements against an authoritative standard.