How land area is calculated
First calculate the flat area, then convert it using exact international land units.
Rectangle A = length × width; triangle A = base × height ÷ 2; circle A = π × radius²; trapezoid A = (a + b) × height ÷ 2; acres = m² ÷ 4,046.8564224; hectares = m² ÷ 10,000.
- Choose the shape closest to your plot. Enter all lengths in the same unit.
- For a rectangle, multiply length by width. For a triangle, multiply base by perpendicular height and divide by 2.
- With three triangle sides, use Heron's formula: s = (a + b + c) ÷ 2; A = √(s × (s − a) × (s − b) × (s − c)). The longest side must be shorter than the other two combined.
- For a circle, use π times radius squared. For a trapezoid, multiply the average of its parallel sides by perpendicular height.
- Convert to square metres using the squared length factor. One acre is exactly 4,046.8564224 m² or 43,560 sq ft. One hectare is 10,000 m².
- Take the square root of the area to find the side of a square with the same area. This is not a claim about your plot's actual boundaries.
Worked example: A plot 100 m long and 100 m wide covers 10,000 m². Dividing by 4,046.8564224 gives 2.4711 acres; dividing by 10,000 gives 1 hectare. A square of the same area has a side of 100 m.
Common land area examples
| Method | Length | Width | Length unit | Known area | Area unit | Acres | Hectares |
|---|---|---|---|---|---|---|---|
| Rectangle | 208.71 ft | 208.71 ft | Feet | — | — | 1.0000 acres | 0.404684 ha |
| Rectangle | 100 m | 100 m | Metres | — | — | 2.4711 acres | 1 ha |
| Convert a known area | — | — | Miles | 1 | sq mi | 640.0000 acres | 258.998811 ha |
| Rectangle | 660 ft | 66 ft | Feet | — | — | 1.0000 acres | 0.404686 ha |
| Convert a known area | — | — | Metres | 1 | Hectares | 2.4711 acres | 1 ha |
Swipe the table sideways to see the rest.
208.71 ft is a rounded square-acre side, so its area is just below one acre before rounding.
Things to consider
- For an irregular plot, split it into rectangles and triangles, then add their areas without overlaps.
- Use horizontal distances, not sloping ground distances.
- A fence length alone does not determine area unless the plot's shape and dimensions are known.
- Use a title or survey plan for legal boundaries and recorded land area.
Frequently asked questions
How big is an acre?
One international acre is exactly 43,560 square feet or 4,046.8564224 square metres. A square acre has a side of about 208.7103 ft or 63.6149 m. An acre measures area, so it can have many different shapes.
What is the difference between acres and hectares?
Both measure land area. One hectare is exactly 10,000 m², while an acre is 4,046.8564224 m². One hectare is about 2.4711 acres; one acre is 0.40468564224 hectares.
How do I measure an irregular plot?
Split the plot into non-overlapping rectangles and triangles. Calculate each part and add the areas, subtracting any excluded sections. For curved or complex boundaries, use the area from a title or survey plan. The Area Calculator covers more simple shapes.
How many acres are in a square mile?
There are exactly 640 acres in one square mile. A mile is 5,280 feet, so a square mile is 27,878,400 sq ft. Divide that by 43,560 to get 640.
Why is an acre 43,560 square feet?
The traditional acre is a rectangle one furlong long and one chain wide. A furlong is 660 feet and a chain is 66 feet; 660 × 66 = 43,560 square feet. These dimensions explain the unit, but a plot of one acre need not have that shape.
Results are estimates for general information only, not financial, medical or professional advice.