Area calculator
Choose a shape, enter its measurements and pick the unit. You get the area, the perimeter where it applies and conversions.
Free · no signup Runs in your browser
How do I calculate area?
Area is the amount of flat surface a shape covers, in square units. Multiply length by width for a rectangle, half the base by the height for a triangle, π times the radius squared for a circle, and the average of the parallel sides times the height for a trapezoid. For a 12 ft by 15 ft room, the area is 180 square feet, which is 16.7 square metres. Pick a shape and a unit, enter the measurements and the calculator gives the area and converts it.
Formulas for each shape
Rectangle: length × width. Square: side². Triangle with a base and height: ½ × base × height. Triangle from three sides: Heron's formula, √(s(s − a)(s − b)(s − c)), where s is half the perimeter; the tool checks that the sides can form a triangle at all. Circle: πr². Ellipse: π × a × b, where a and b are the two semi-axes. Trapezoid: ½(a + b) × h. Parallelogram: base × height, with the height measured at right angles to the base. Rhombus: half the product of the diagonals. Circle sector: the fraction of the circle, angle ÷ 360, times πr². Ring (annulus): π(R² − r²). Regular polygon with n sides of length s: n × s² ÷ (4 × tan(π ÷ n)).
Always use the same unit for all the measurements, and remember that area is in square units: a side of 3 m gives 9 m², and doubling every side multiplies the area by four, not two. To change units, convert the area, not the length factor: 1 m² is 10.7639 ft², not 3.28 ft².
It runs in your browser. Nothing you enter is sent anywhere, and there is no sign-up.
Everyday uses in Canada
Floor space is listed in square feet in most Canadian real estate, while building plans, flooring and paint are often given in square metres; a condo of 650 ft² is 60.4 m². Lots are described in acres or square feet, farmland in acres or hectares, and a Prairie quarter section of 160 acres is 64.75 hectares. For a room of flooring, add 5 to 10% for cuts and waste. For many conversions at once, use the square feet to square metres converter or the hectares to acres converter, and for a three-dimensional shape the volume calculator.
When to use it
- Flooring, paint, sod, tile or roofing quantities
- Lot, garden or room sizes
- Geometry homework
- Comparing a listing in square feet with one in square metres
Mistakes it helps you avoid
- Mixing units, such as feet and inches, in one calculation.
- Using a slanted side instead of the perpendicular height.
- Converting an area with the length factor instead of its square.
- Forgetting the waste allowance when buying material.
The formula
How the answer is worked out.
rectangle = l × w; triangle = ½ b h; circle = π r²; trapezoid = ½ (a + b) h; parallelogram = b htriangle from three sides: s = (a + b + c) ÷ 2; area = √(s (s − a)(s − b)(s − c))ellipse = π a b; rhombus = ½ p q; sector = (angle ÷ 360) π r²; ring = π (R² − r²)regular polygon = n s² ÷ (4 tan(π ÷ n)); 1 m² = 10.7639 ft², 1 acre = 4,046.8564224 m², 1 ha = 10,000 m²
Unit factors are exact definitions from NIST SP 811. The ellipse perimeter uses Ramanujan's approximation, since there is no simple exact formula. Results are shown to six decimal places with trailing zeros removed.
Example: a 12 ft by 15 ft room
Flooring is needed for a room 12 ft by 15 ft.
- Area12 × 15 = 180 ft²
- In square metres180 × 0.09290304 = 16.72 m²
- With 10% waste198 ft²
180 ft² (16.72 m²)
Order about 198 ft² of flooring.
Terms on this page
- Area
- The amount of flat surface a shape covers, in square units.
- Perimeter
- The distance around a shape.
Common questions
What is the area of a circle?
π times the radius squared.
How do I find the area of a triangle?
Half the base times the height, or Heron's formula if you know all three sides.
How many square feet are in a square metre?
10.7639.
How do I find the area of an irregular shape?
Split it into rectangles, triangles and circles, find each area and add them.
Is my data uploaded?
No.
Is anything I enter sent to a server?
No. The calculation happens in your browser and nothing you type leaves your device.
Where these numbers come from
- Wikipedia — Area Area formulas for common shapes.
- Wikipedia — Heron's formula Area of a triangle from its three sides.
- Wikipedia — Ellipse Area and the approximate perimeter.
- NIST — Guide for the Use of the International System of Units, Appendix B.8 (conversion factors) The exact definitions used for inches, feet, yards, miles, acres and gallons.
Last verified 2026-10-25 The method on this page is checked against the sources above at least once a year. Spotted something out of date? Tell us and we will fix it.
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