How to calculate an area
Choose the outline that matches your shape. Enter its measurements in one length unit, then read the area in square units.
Rectangle A = l × w; circle A = πr²; triangle A = ½bh
- Square and rectangle areas multiply two perpendicular lengths. A parallelogram uses its base and perpendicular height.
- A triangle uses half its base times height. A trapezoid uses the average of its parallel bases times height.
- A circle uses πr², a semicircle uses half of that, and a sector uses the angle's fraction of a full 360-degree circle.
- An ellipse uses πab with semi-axes a and b. A rhombus uses half the product of its diagonals.
- A regular polygon has equal sides and angles. Its area is n × s² ÷ (4 × tan(π ÷ n)), with the tangent evaluated in radians.
- Area conversions square the length factor. One square foot is exactly 0.09290304 square metres.
Worked example: A rectangular floor 4 m long and 3 m wide has A = 4 × 3 = 12 m², or 129.1669 ft².
Area examples by shape
| Shape | Measurements | Area |
|---|---|---|
| Square | Side 5 | 25 m² |
| Rectangle | Length 4, width 3 | 12 m² |
| Triangle | Base 10, height 5 | 25 m² |
| Circle | Radius 10 | 314.1593 m² |
| Semicircle | Radius 10 | 157.0796 m² |
| Ellipse | Semi-axes 5 and 3 | 47.1239 m² |
| Parallelogram | Base 8, height 4 | 32 m² |
| Trapezoid | Bases 8 and 5, height 4 | 26 m² |
| Rhombus | Diagonals 6 and 8 | 24 m² |
| Sector | Radius 10, angle 90° | 78.5398 m² |
| Regular polygon | 6 sides, side length 2 | 10.3923 m² |
Swipe the table sideways to see the rest.
All length measurements in this table are metres. Each row uses the same helper as the calculator.
Things to consider
- For an L-shaped floor, split it into two rectangles without overlapping them.
- Measure a triangle's height at a right angle to its base, not along a sloping edge.
- Halve a circle's diameter to get its radius, and halve an ellipse's full axes to get its semi-axes.
- For materials, allow for cuts and waste separately from the measured area.
Frequently asked questions
What is area?
Area measures how much surface a flat shape covers. It is expressed in square units such as cm², m² or ft².
How do I work out the area of a room or floor?
For a rectangular floor, multiply its length by its width. For an L-shaped room, divide it into non-overlapping rectangles and add their areas. The Rectangle Calculator: Area and Perimeter also gives the distance around each rectangle.
How do I convert square metres to square feet?
Divide square metres by 0.09290304. One m² is about 10.7639 ft². Square the length conversion factor rather than using a metres-to-feet factor once.
What are hectares and acres?
They are units of land area. One hectare is exactly 10,000 m², and one international acre is exactly 4,046.8564224 m². One hectare is about 2.4711 acres.
How do I find the area of an irregular shape?
Split it into simple shapes, calculate each area and add them. Subtract any holes or cut-outs. Curved or surveyed boundaries may need coordinates or a more specialised method.
What is the difference between area and perimeter?
Area is the surface inside a boundary, measured in square units. Perimeter is the length around that boundary, measured in length units. Two shapes can have the same area but different perimeters.
Results are estimates for general information only, not financial, medical or professional advice.