How many square megameters are in 1 acre?

1 acre equals 4.046856e-9 square megameters, using the exact defined conversion factor rather than an estimate.

How do I convert acre to square megameter?

Multiply the acre value by 4.046856e-9. The converter above does this instantly to whatever precision you set.

How do I convert square megameter back to acre?

Use the reverse factor: 1 square megameter equals 247,105,381.5 acres. You can also use the swap control in the converter above to flip the direction instantly.

What is a square megameter?

Square Megameter (Mm2) is a unit of area.

Is the acre to square megameter 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.

Acres to Square Megameters Converter

Q: 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.

About Converting Acres to Square Megameters

Comparing Acre 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. Acre is most often used for measuring farmland, ranch, and rural property size in the us.

Formula

square megameters = acres × 4.046856e-9

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 megameter equals 1e+12 base units, so dividing one by the other gives the direct acre-to-square megameter factor of 4.046856e-9.

Simple example

1 ac × 4.046856e-9 = 4.046856e-9 Mm2

1 acre = 4.046856e-9 square megameters.

Real-world example

10 ac × 4.046856e-9 = 4.046856e-8 Mm2

10 acres = 4.046856e-8 square megameters.

Conversion table

Acre (ac)	Square Megameter (Mm2)
1 ac	4.046856e-9 Mm2
5 ac	2.023428e-8 Mm2
10 ac	4.046856e-8 Mm2
25 ac	1.011714e-7 Mm2
50 ac	2.023428e-7 Mm2
100 ac	4.046856e-7 Mm2

Reverse conversion: Square Megameter to Acre

4.046856e-9 Mm2 × 247105381.5 = 0.9999998956 ac

4.046856e-9 square megameters = 0.9999998956 acres.

acres = square megameters × 247105381.467

For a page dedicated to this direction, see Square Megameter 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 Megameter (Mm2)

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.

Acres to Square Megameters Converter — ac to Mm2

Area Converter