Acres to Square Kilometers
Type a value in either box to convert between acres and square kilometers. The factor is 0.00404686.
| Acres | Square Kilometers |
|---|---|
| 1 ac | 0.004047 km² |
| 2 ac | 0.008094 km² |
| 3 ac | 0.012141 km² |
| 5 ac | 0.020234 km² |
| 10 ac | 0.040469 km² |
| 25 ac | 0.101171 km² |
| 50 ac | 0.202343 km² |
| 100 ac | 0.404686 km² |
How to use
- Enter a value in the Acres field.
- The Square Kilometers figure appears immediately — no button to press.
- Typing in the Square Kilometers field converts back to Acres the same way.
- Use the reference table for the values that come up most often.
Acres to Square Kilometers formula
Converting acres to square kilometers is a single multiplication by 0.00404685642.
km² = ac × 0.00404685642
Why this factor: the acre and the square kilometer are both defined against the square meter, so dividing one definition by the other gives 0.00404685642 directly. Both definitions are set out in full below.
To go the other way, divide by 0.00404685642 — or use the Square Kilometers to Acres converter, which is the same calculation reversed.
Worked example
Given 250 ac, multiplying by 0.00404685642 yields 1.011714 km².
250 ac × 0.00404685642 = 1.011714 km²
The converter above does this for any value you type, in either direction.
What is an acre?
An acre is the customary land area unit of the US and UK, historically a day's ploughing for one team of oxen.
Definition: One chain by one furlong — 43,560 square feet — which is exactly 4,046.8564224 square meters.
Where it is used: US and UK property and farmland, development parcels, and land sales.
Worth knowing: 640 acres make one square mile, the basis of the US Public Land Survey grid.
What is a square kilometer?
A square kilometer is the area of a one-kilometer square — one million square meters.
Definition: Exactly 1×10⁶ square meters. Note it is the kilometer that is squared, not the prefix applied to a square meter.
Where it is used: City, national park and country areas, population density, and land cover statistics.
Acres vs Square Kilometers
The acre is an imperial unit while the square kilometer is a metric unit. That is why the factor between them is not a round number: the two systems were defined independently and only later tied together by exact agreement.
Frequently asked questions
How many square kilometers are in an acre?
One acre equals 0.00404685642 square kilometers.
What is the formula to convert acres to square kilometers?
Multiply the number of acres by 0.00404685642. To reverse it, divide by 0.00404685642 instead.
How do I convert square kilometers back to acres?
Divide by 0.00404685642, which is the same as multiplying by 247.105381.
How many square kilometers are in 10 acres?
10 ac works out to 0.040469 km².
Is there anything to watch out for with acres?
640 acres make one square mile, the basis of the US Public Land Survey grid.
How is the acre defined?
One chain by one furlong — 43,560 square feet — which is exactly 4,046.8564224 square meters.