Area converter
Convert between square metres, square feet, square yards, acres, hectares and square miles. Exact factors, and why you cannot square a length conversion.
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Every area unit, one page
Pick any two units above. The conversions people look up most often have dedicated pages with reference tables, linked below.
The factors are exact
Each imperial area unit is the square of an exactly-defined length, so the area factors are exact too:
| Unit | Square metres | Note |
|---|---|---|
| Square centimetre | 0.0001 | |
| Square metre | 1 | |
| Square kilometre | 1,000,000 | |
| Hectare | 10,000 | 100 m × 100 m |
| Square foot | 0.09290304 | 0.3048² |
| Square yard | 0.83612736 | 9 square feet |
| Acre | 4046.8564224 | 4840 square yards |
| Square mile | 2,589,988.110336 | 640 acres |
You cannot square a length conversion in your head
This is the mistake that ruins a room estimate. A metre is 3.28 feet, so it is tempting to think a square metre is 3.28 square feet. It is 10.76 square feet — 3.28 squared.
| Length ratio | Area ratio |
|---|---|
| 1 m = 3.28 ft | 1 m² = 10.76 ft² |
| 1 km = 0.621 mi | 1 km² = 0.386 mi² |
| 1 in = 2.54 cm | 1 in² = 6.45 cm² |
The same trap runs the other way for volume, where the factor is cubed: a cubic metre is 35.3 cubic feet, not 3.28.
The acre is a medieval unit and it shows
An acre was the area a team of oxen could plough in a day: one furlong long by one chain wide, which is 220 yards by 22 yards. That is why it is 4840 square yards rather than any round number, and why it does not relate neatly to anything else.
| Square feet | Square metres | |
|---|---|---|
| Acre | 43,560 | 4046.86 |
| Hectare | 107,639 | 10,000 |
A hectare is about 2.47 acres. A football pitch is roughly 0.7 hectares, or 1.76 acres, which is the usual reason both units get quoted in the same news story.
Property is measured differently everywhere
The unit a home is sold in is a matter of local convention, not of physics:
| Where | Unit | In square metres |
|---|---|---|
| United States, Hong Kong | square foot | 0.0929 |
| Continental Europe, mainland China | square metre | 1 |
| Taiwan | 坪 (ping) | 3.3058 |
| Japan | 帖 / 畳 (jō, tatami) | ~1.62, and it varies by region |
Worse, “area” itself is not one thing. A listing may quote gross floor area, saleable area, or usable area, and the difference between them can be 20% or more for the same apartment. Converting the number is the easy part; knowing which number you were given is not.
Where people go wrong
Square feet is not feet squared in the way it looks. A room described as “12 by 15” is 180 square feet. A room described as “180 feet” is a sentence with a missing word.
A square kilometre is not a thousand square metres. It is a million. The prefix applies to the length before it is squared.