21 acres to hectares
8.50 ha
21 ac = 8.50 ha.
hectares
8.50ha
21 ac = 8.50 ha
The short answer
How many hectares is 21 acres?
21 ac = 8.50 ha. 1 acre = 0.404686 hectares, so the working is 21 × 0.404686 = 8.50.
The working
The factor below is an exact definition rather than a measurement, so nothing is approximated in the arithmetic. The only rounding on this page happens where a number is displayed.
1 acre = 0.404686 hectares 21 × 0.404686 = 8.50
How much precision do you need?
Each row is the same answer cut at a different number of decimals, with what that choice costs you. Pick the shortest row whose error is smaller than whatever you are measuring with.
| Rounded to | Answer (ha) | Off by |
|---|---|---|
| Whole number | 8 | −0.49840 |
| 1 decimal | 8.5 | +0.00160 |
| 2 decimals | 8.50 | +0.00160 |
Round trip: take 8.50 ha back the other way and you land on 21.0040 ac — a drift of 0.0040 ac. That gap is the rounding, not the conversion.
What 21 ac looks like
22 ac
Alcatraz Island in San Francisco Bay is 22 acres of rock, now run by the National Park Service.
Frequently asked questions
What is 21 acres in hectares?
21 acres is 8.50 hectares. 1 acre = 0.404686 hectares, so the working is 21 × 0.404686 = 8.50.
How accurate is 8.50 ha?
Rounding to 8.50 ha and converting straight back gives 21.0040 ac, a drift of 0.0040 ac from the 21 you started with. The factor itself is exact; every bit of that difference comes from the rounding, not the conversion.
Nearby values
Any value at all
Acres to Hectares Converter
Land area from acres to hectares, with the exact survey-derived factor.
Open the acres to hectares converter →