Area Calculator

This free area calculator finds the area of the shapes people measure most often: rectangles, squares, triangles, circles, trapezoids, parallelograms, rhombuses, ellipses, sectors, rings and regular polygons. Choose a shape, pick feet, inches, yards, metres, centimetres or millimetres, and type in the measurements. You get the area in square units, the formula, the working, and the same area in other units such as square metres, square feet and acres.

Under the calculator you will find the formula for each shape with a worked example, a short guide to square unit conversion, and what to do when your shape is not on the list: L-shaped rooms, irregular plots, shapes you only have a picture of. Every other area calculator on this site is linked at the bottom, so you can jump to a specialist tool for floors, walls, roofs, land or surface area.

Pick a shape to start

Tap a shape and the calculator below switches to it.

12 shapes6 length unitsFormula and working shownFree, no sign-up

Area Calculator for 12 Shapes

Pick a shape, choose your unit, enter the measurements. The area updates as you type.

Use one length unit for every measurement. The result is in that unit squared, with conversions below it. Area is not the same as the amount of material to buy; see the notes further down.

How to Use the Area Calculator

  1. Choose the shape. If you only know the three sides of a triangle, pick “Triangle (three sides)”. If you know the radius, diameter or circumference of a circle, pick “Circle” and then say which one you have.
  2. Choose the length unit. Use the same unit for every measurement. The area comes out in that unit squared, for example ft² if you measured in feet.
  3. Enter the measurements. Heights must be perpendicular to the base. Angles are in degrees.
  4. Read the result. The area, the formula and the working appear below the form. Open “Same area in other units” to see the conversions.

Why the calculator sometimes shows an error

The calculator only accepts numbers greater than zero. For three-sided triangles each side must be shorter than the other two combined, otherwise no triangle exists. A ring needs an inner radius smaller than the outer radius, and a sector needs an angle of 360 degrees or less.

Area Formulas for Common Shapes

Each formula below is the one the calculator uses. If you want the working for your own numbers, enter them above and compare.

RectangleLength × Width
SquareSide × Side
Triangle (base, height)½ × Base × Height
Triangle (3 sides)Heron’s formula
Circleπ × Radius²
Sector(Angle ÷ 360) × π × R²
Ellipseπ × (W ÷ 2) × (H ÷ 2)
Ringπ × (R² − r²)
Trapezoid((a + b) ÷ 2) × Height
ParallelogramBase × Height
Rhombus or kite½ × Diagonal 1 × Diagonal 2
Regular polygon(n × Side²) ÷ (4 × tan(180° ÷ n))

Rectangles and squares

Area = Length × Width

Where Length and Width are the two adjacent sides. A square is the special case where both are equal, so Area = Side × Side.

Example: a room is 12 ft long and 9 ft wide. Area = 12 × 9 = 108 ft². In square metres that is about 10.03 m². For rooms, floors and walls with several sections, use the floor area calculator or the wall area calculator.

Triangles

Triangle from base and height

Area = ½ × Base × Height

Where Base is any side you choose and Height is the perpendicular distance from that side to the opposite corner. Example: a gable end is 24 ft wide and 8 ft tall at the peak. Area = 0.5 × 24 × 8 = 96 ft².

Triangle from three sides (Heron’s formula)

s = (a + b + c) ÷ 2 Area = √(s × (s − a) × (s − b) × (s − c))

Where a, b and c are the side lengths and s is the semi-perimeter. Example: sides of 7 cm, 8 cm and 9 cm. s = 12, so Area = √(12 × 5 × 4 × 3) = √720 ≈ 26.83 cm². More triangle types are covered by the right triangle, isosceles triangle and irregular triangle calculators.

Circles, sectors, ellipses and rings

Area of a circle = π × Radius²

Where π ≈ 3.14159 and Radius is the distance from the centre to the edge. If you know the diameter, halve it first. If you know the circumference, divide it by 2π. Example: a round pond with a radius of 3 m has an area of π × 3² ≈ 28.27 m².

Sectors, ellipses and rings

A sector is a slice of a circle. Example: a radius of 10 and an angle of 90° gives (90 ÷ 360) × π × 10² ≈ 78.54. An ellipse with a full width of 8 and a full height of 5 has an area of π × 4 × 2.5 ≈ 31.42. A ring with an outer radius of 5 and an inner radius of 3 has an area of π × (25 − 9) ≈ 50.27. Related tools: circle area calculator, sector area calculator, ellipse area calculator and circle with hole area calculator.

Trapezoids, parallelograms, rhombuses and kites

Trapezoid

Trapezoid area = ((a + b) ÷ 2) × Height

Where a and b are the two parallel sides and Height is the distance between them. Example: parallel sides of 10 m and 6 m with a height of 4 m give ((10 + 6) ÷ 2) × 4 = 32 m².

Parallelogram

Parallelogram area = Base × Height

Example: a base of 15 ft and a perpendicular height of 6 ft gives 90 ft². Note that the height is not the slanted side.

Rhombus and kite

Rhombus or kite area = ½ × Diagonal 1 × Diagonal 2

Example: diagonals of 10 and 6 give 0.5 × 10 × 6 = 30. For shapes with sides that do not match these neat forms, see the irregular parallelogram, rhombus and kite area calculator and the irregular trapezoid area calculator.

Regular polygons

Area = (n × Side²) ÷ (4 × tan(180° ÷ n))

Where n is the number of equal sides and Side is the length of one side. Example: a regular hexagon with 4 m sides has an area of (6 × 16) ÷ (4 × tan 30°) ≈ 41.57 m². The regular polygon area calculator and octagon calculator add more detail for these shapes.

How the shapes compare

The chart shows the area of six shapes that all fit inside the same 10 × 10 box. It makes two useful rules of thumb visible: a triangle or rhombus is exactly half of the box, and a circle covers about 78.5% of the square around it (π ÷ 4).

Area inside the same 10 × 10 box

Area in square units. The full box is 100.

Rectangle
100
Parallelogram
100
Trapezoid (10 and 6)
80
Ellipse (10 × 10)
78.54
Triangle
50
Rhombus (diagonals 10, 10)
50

Converting Square Units

Area units are squares of length units, so the conversion factor is squared too. One foot is 0.3048 m, so one square foot is 0.3048² = 0.092903 m². The calculator does this for you, but these exact relationships are useful to remember:

RelationshipValue
1 ft²144 in²
1 yd²9 ft²
1 m²10,000 cm²
1 m²about 10.7639 ft²
1 acre43,560 ft²
1 hectare10,000 m²

To go from square feet to square metres, multiply by 0.092903. To go the other way, multiply by 10.7639. For a dedicated tool, use the area unit conversion calculator or the surface area unit converter.

Area Is Not the Same as the Amount of Material to Buy

The calculator gives the area a shape covers. It does not tell you how much flooring, paint, turf or tile to buy. Material quantity depends on the product’s coverage, how it is packaged, the pattern or layout, cuts, openings such as doors and windows, and any waste allowance. Work out the area first, then check the product label for its coverage.

When Your Shape Is Not on the List

Real spaces are often not clean geometric shapes. There are three common ways to handle them:

If your shape is genuinely irregular, the irregular shape area calculator on the homepage lets you draw it, trace it over an image or enter its coordinates. For step-by-step methods with examples, read the best methods to measure the area of irregular shapes.

All Area Calculators

This page is for quick checks across common shapes. Each calculator below goes deeper on one shape, room or situation, with its own inputs, examples and guidance, so pick the one that matches what you are measuring.

Draw, trace and irregular shapes

Basic shapes

Triangles

Rooms, floors and walls

Land, garden and outdoor areas

Surface area (3D shapes)

Units, scale and guides

Area Calculator FAQ

Measuring and units

How do I find the area of a shape when I only know its sides?

For a rectangle or parallelogram you also need a height or an angle, because sides alone do not fix the area. For a triangle, three sides are enough: choose “Triangle (three sides)” and the calculator applies Heron’s formula. For regular polygons, one side length and the number of sides are enough.

How do I convert square feet to square metres?

Multiply square feet by 0.092903 to get square metres. To convert square metres to square feet, multiply by 10.7639. The calculator shows both automatically under “Same area in other units”.

Which unit should I choose?

Choose the unit you measured in and use it for every measurement. The area is returned in that unit squared, and the other units are shown as conversions.

How do I find the area of an L-shaped room or other irregular shape?

Split the outline into rectangles or triangles, find each area, and add them together. Subtract any parts that are cut out. If you have corner coordinates, a photo or a floor plan, the irregular polygon, image and draw calculators linked above do the work for you.

Why does the triangle calculator say my sides are invalid?

Three lengths only form a triangle if each one is shorter than the sum of the other two. If one side is as long as or longer than the other two combined, the sides cannot meet and no area exists.

Area, materials and surface area

Is area the same as the amount of flooring or paint I need?

No. Area is the size of the surface. The quantity to buy also depends on the product’s coverage, packaging, layout, openings and waste allowance, so check the product label after you have the area.

What is the difference between area and surface area?

Area measures a flat, two-dimensional shape. Surface area is the total area of all the faces or curved surfaces of a three-dimensional object such as a box, cylinder or sphere. The surface area calculators linked above cover those solids.