Choose a shape, enter its dimensions in one unit, and calculate its area. The result includes square metres, square feet, square yards, acres and hectares. For an irregular room, calculate the simple sections separately and combine them using the examples below.
Area Calculator
Calculate the area of any common shape — rectangle, square, triangle, circle, ellipse, trapezoid, parallelogram, sector, rhombus and regular polygon — with land conversions to acres and hectares.
All units
Note: Enter all dimensions in the same unit. Acre and hectare conversions are useful for land and flooring; angle for the sector is in degrees.
Measure the dimension the formula actually needs
For a triangle or parallelogram, height means the perpendicular distance to the base, not a sloping side. For a circle, radius is half the diameter. Entering a circle’s diameter in a radius field makes the area four times too large.
For an ellipse, check whether the inputs request full axes or semi-axes: the formula A = πab uses the two semi-axis lengths. A regular polygon requires equal sides and equal angles; the same formula cannot be used for an arbitrary plot with that number of sides.
Worked example: an L-shaped floor
Sketch the space as a 6 m by 5 m outer rectangle with a 2 m by 2 m corner removed. Calculate both rectangles, then subtract:
Outer area = 6 × 5 = 30 m²Missing corner = 2 × 2 = 4 m²Floor area = 30 − 4 = 26 m²
You can instead split the L into non-overlapping rectangles and add their areas. Each part must be counted once. The displayed result is geometric area; it does not automatically include cutting waste, gaps, openings or a supplier’s ordering allowance.
Convert units before combining shapes
A room 4 m long and 350 cm wide is 4 × 3.5 = 14 m². Multiplying 4 by 350 before converting units would mix metres and centimetres. For feet and inches, first convert to one decimal unit: 8 feet 6 inches is 8.5 feet.
Check the distinction between length and area conversions. One metre is 100 centimetres, but one square metre is 10,000 square centimetres. An area factor is the square of the corresponding length factor.
For the underlying rectangle, triangle and trapezoid methods, see OpenStax’s geometry explanations. Use the Unit Converter to align measurements before calculating.
How to use this calculator
- Select the shape that matches the surface you are measuring.
- Choose the measurement unit before entering dimensions. Changing the shape or unit clears the inputs.
- Enter positive dimensions. Use the perpendicular height for triangles, parallelograms and trapezoids; use the radius for circles and sectors.
- Select Calculate Area. Results are rounded for display, so keep your original measurements when comparing small differences.
Formulas used by each shape
| Shape | Area formula | Required measurements |
|---|---|---|
| Rectangle | L × W | Length and width |
| Square | s² | One side |
| Triangle | b × h ÷ 2 | Base and perpendicular height |
| Circle | πr² | Radius, half the diameter |
| Ellipse | πab | Two semi-axes, each half a full axis |
| Trapezoid | (a + b) × h ÷ 2 | Two parallel sides and perpendicular height |
| Parallelogram | b × h | Base and perpendicular height |
| Circle sector | (θ ÷ 360) × πr² | Radius and angle in degrees, up to 360° |
| Rhombus | d₁ × d₂ ÷ 2 | Both diagonals |
| Regular polygon | n × s² ÷ [4 tan(π/n)] | Whole number of sides n ≥ 3 and side length s; the formula uses radians |
A regular polygon has equal sides and equal interior angles. This formula does not measure an arbitrary land plot from its side lengths alone.
Worked checks you can reproduce
- Rectangular room: 12 ft × 10 ft = 120 ft², equivalent to 11.148 m² after rounding.
- Triangular bed: a base of 6 m and perpendicular height of 4 m give 6 × 4 ÷ 2 = 12 m².
- Circular surface: radius 2 m gives π × 2² ≈ 12.566 m². A diameter of 2 m instead gives a radius of 1 m and an area of about 3.142 m².
Area conversion reference
One square foot equals 0.09290304 m²; one square yard equals 9 ft²; one acre equals 43,560 ft² or 4,046.8564224 m²; one hectare equals 10,000 m². These factors refer to the international foot.
From measured area to an order quantity
Area is only the starting point for buying materials. For example, a 26 m² floor with a chosen 10% allowance needs 26 × 1.10 = 28.6 m². If each pack covers 2.2 m², that example needs 13 packs. The 10% figure is an example, not a rule: layout, cut patterns, product instructions and supplier requirements determine the allowance.
Paint also depends on coverage per coat; concrete and soil need a depth to turn area into volume. Use the paint calculator or concrete calculator only after checking their required inputs.
Limits and common questions
Can I enter feet and inches together?
Convert the measurement to one unit first. For example, 8 ft 6 in is 8.5 ft, not 8.6 ft.
Does this measure a sloping roof or a property boundary?
No. The calculator uses the dimensions you supply for flat geometric shapes. It does not measure roof slope, read maps, verify boundaries or establish a legal floor-area definition. Use a qualified surveyor or relevant professional when a project requires those measurements.
How precise is the answer?
The result depends on measurement accuracy, the selected shape and computer rounding. More decimal places do not make a tape measurement more accurate. Negative lengths, fractional side counts and sector angles above 360° are rejected.
Calculation checks: 1 October 2026. Maintained by Umar Malik. The ten shape formulas and invalid-input messages were checked with worked examples.
Formula reference: OpenStax: rectangles, triangles and trapezoids. Read our editorial policy or report a calculation error with the shape, units, inputs and expected result.