About the Area Calculator
Area Calculator works out the area, and where the shape has one the perimeter, of eleven flat shapes: square, rectangle, triangle, circle, ellipse, trapezoid, parallelogram, rhombus, regular polygon, sector of a circle and ring. Pick the shape and a unit from millimetres to yards, type the measurements shown beside a small sketch, and the answer appears with the same area in square metres, square centimetres, square feet, square yards, acres and hectares. Optional fields, such as the sloping sides of a trapezoid, add the perimeter when you fill them in. The formulas are for flat, straight-sided shapes measured in one unit. The ellipse perimeter is an approximation that is very accurate for ordinary shapes, and land or roof measurements should always be checked on site.
Updated October 2026
How to use the Area Calculator
- 1Choose the shape and the unit you measured in.
- 2Type each measurement, using the sketch to see which is which.
- 3Fill in the optional sides if you also want the perimeter.
- 4Read the area, the perimeter and the conversion table.
- 5Copy the result or change the unit to see the area in it.
Choosing the right formula
Every shape in the list has its own formula, and the sketch shows which measurement belongs to which field. Use the height that is perpendicular to the base for triangles and parallelograms, not the slanted side. For a rhombus, use its two diagonals.
A regular polygon has equal sides and equal angles. Its area uses the number of sides and the side length, for example about 10.39 square units for a hexagon with sides of 2. A sector is a slice of a circle, and the ring is the flat band between two circles.
Units and square units
Enter every measurement in the same unit. The result is in that unit squared, so centimetres give square centimetres. The table converts the same area into other common units, including acres and hectares for land.
One hectare is 10,000 square metres, and one acre is about 4,046.86 square metres. To convert plain lengths or other kinds of units, use Unit Converter. Once you know the area, use the Volume Calculator for the third dimension, or the Unit Converter if the answer is in the wrong unit.
Breaking a room or plot into shapes
- Sketch the outline and split it into rectangles and triangles.
- Measure each piece and calculate its area.
- Add the areas together and subtract any cut-outs, such as a bay or a pillar.
- Add a percentage for waste when you buy tiles, paint or flooring; Percentage Calculator helps with that.
Common mistakes
- Mixing units, such as a length in metres and a width in centimetres.
- Using the diameter where the radius is needed.
- Using a slanted side instead of the perpendicular height.
- Forgetting that converting area needs the square of the length factor.
- Trusting a plan measurement for a purchase; check measurements on site.
Features
- Eleven shapes, including sector, ring and regular polygon
- Area and perimeter or circumference
- Units mm, cm, m, in, ft and yd
- Conversion to m², cm², ft², yd², acres and hectares
- Sketch of the shape with the field names
- Clear messages for missing or impossible measurements
- Runs in your browser
Frequently asked questions
How do I calculate the area of a rectangle?
Multiply the length by the width. A room 5 metres long and 3 metres wide has an area of 15 square metres. Choose Rectangle, type both measurements and the tool also gives the perimeter, 16 metres, and the area in square feet.
What is the area of a circle formula?
The area is π times the radius squared. With a radius of 2, that is about 12.57 square units. If you know the diameter, halve it first to get the radius. The circumference, 2πr, is shown under the area.
How do I find the area of an irregular shape?
Split it into simple shapes such as rectangles and triangles, find the area of each, and add them up. Subtract any parts that are cut out. Use one shape at a time in this calculator and add the results by hand.
How do I convert square feet to square metres?
Multiply by 0.09290304, because one foot is 0.3048 metres and area uses the square of that. To do it here, choose the unit ft, type your measurements, and read the result in the m² row of the table.
What is the area of a trapezoid?
Add the two parallel sides, divide by two and multiply by the height. Parallel sides of 4 and 6 with a height of 3 give 15. Enter the sloping sides too if you want the perimeter.
Why are area units squared?
Area counts how many unit squares fit inside a shape, so a length in metres becomes square metres. Doubling the sides of a square makes its area four times bigger, which is why the conversion factor between units is squared as well.