An international acre is 4,046.8564224 square meters.
Acres to Square Gigameters Converter — ac to Gm2
Convert Acre (ac) to Square Gigameter (Gm2) using the exact conversion factor (1 acre = 4.046856e-15 square gigameter). See the formula, worked examples, conversion table, history, and common uses.
Acres to Square Gigameters 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 4046.856422 / 1e+18.
Area uses the square meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Acres to Square Gigameters
Comparing Acre and Square Gigameter 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. Acre is most often used for measuring farmland, ranch, and rural property size in the us.
Formula
square gigameters = acres × 4.046856e-15
This factor comes from each unit's defined relationship to the category's base unit: 1 acre equals 4046.8564224 base units, and 1 square gigameter equals 1e+18 base units, so dividing one by the other gives the direct acre-to-square gigameter factor of 4.046856e-15.
Simple example
1 ac × 4.046856e-15 = 4.046856e-15 Gm2
1 acre = 4.046856e-15 square gigameters.
Real-world example
10 ac × 4.046856e-15 = 4.046856e-14 Gm2
10 acres = 4.046856e-14 square gigameters.
Conversion table
| Acre (ac) | Square Gigameter (Gm2) |
|---|---|
| 1 ac | 4.046856e-15 Gm2 |
| 5 ac | 2.023428e-14 Gm2 |
| 10 ac | 4.046856e-14 Gm2 |
| 25 ac | 1.011714e-13 Gm2 |
| 50 ac | 2.023428e-13 Gm2 |
| 100 ac | 4.046856e-13 Gm2 |
Reverse conversion: Square Gigameter to Acre
4.046856e-15 Gm2 × 2.471054e+14 = 0.9999998956 ac
4.046856e-15 square gigameters = 0.9999998956 acres.
acres = square gigameters × 2.471054e+14
For a page dedicated to this direction, see Square Gigameter to Acre.
Understanding the Acre
Acre (ac) measures area. The international acre is defined as exactly 4,046.8564224 square meters. It is classified as a US/imperial customary unit.
Where it's used: United States United Kingdom (informal/historical, land registry legacy) Countries with historical British land-survey systems
International acre vs. US survey acre. The US survey acre, based on the US survey foot, differs from the international acre by about two parts per million. The US retired the survey foot/acre for federal use at the end of 2022.
Uses of the Acre today
- Measuring farmland, ranch, and rural property size in the US
- Real estate listings and zoning for land parcels
- Forestry and land-management reporting
History of the Acre
The acre originated in medieval England as a practical field measurement: the area a yoke of oxen could plow in one day, roughly a furlong (660 ft) long by a chain (66 ft) wide, giving the 43,560 square feet still used today.
Edward I's 1305 statute formalized this figure. In 1959, the same International Yard and Pound Agreement that fixed the pound also fixed the international acre at exactly 4,046.8564224 m², though the US separately retained a slightly different 'US survey acre' for some legacy land records until it was phased out in 2023.
Historical origin. Acre was not the invention of a single named person; it developed through the process described above.
Understanding the Square Gigameter (Gm2)
Square metric area unit.
Acre — sources
- NIST — US Survey Foot: Revised Unit Conversion Factors — Documents the 1959 international acre definition and the 2022/2023 survey-foot retirement.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many square gigameters are in 1 acre?
1 acre equals 4.046856e-15 square gigameters, using the exact defined conversion factor rather than an estimate.
How do I convert acre to square gigameter?
Multiply the acre value by 4.046856e-15. The converter above does this instantly to whatever precision you set.
How do I convert square gigameter back to acre?
Use the reverse factor: 1 square gigameter equals 2.471054e+14 acres. You can also use the swap control in the converter above to flip the direction instantly.
What is a acre?
Acre (ac) measures area. The international acre is defined as exactly 4,046.8564224 square meters. It is classified as a US/imperial customary unit.
What is a square gigameter?
Square Gigameter (Gm2) is a unit of area.
Is the acre to square gigameter conversion exact?
Yes. The international acre is defined as exactly 4,046.8564224 square meters. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
What is the difference between international acre vs. us survey acre?
The US survey acre, based on the US survey foot, differs from the international acre by about two parts per million. The US retired the survey foot/acre for federal use at the end of 2022.
Where is the acre still used today?
United States United Kingdom (informal/historical, land registry legacy) Countries with historical British land-survey systems