Area and volume: two measures, two uses
Area (or surface area) measures a flat surface: it is expressed in square units, such as the square metre. Volume measures the space occupied by a solid: it is expressed in cubic units, such as the cubic metre or the litre. Confusing the two is the most frequent mistake in home improvement — you buy paint to cover square metres of wall, but concrete to fill cubic metres of foundation.
This calculator covers the usual shapes in both families. For surfaces: rectangle, triangle and circle. For volumes: cube and cuboid, cylinder, sphere and cone. You choose the shape, enter its dimensions, and the result appears instantly with the exact formulas of classical geometry.
The formulas to know
For surfaces, three formulas cover most needs: the area of a rectangle is length × width; that of a triangle is (base × height) ÷ 2, whatever its shape; that of a circle is π × radius², about 3.1416 times the square of the radius. A frequent trick: for an L-shaped room, split it into two rectangles and add the two areas.
For volumes, the logic is the same in three dimensions: a cuboid is calculated as length × width × height; a cylinder as π × radius² × height, i.e. the area of the base disc multiplied by the height; a sphere is 4/3 × π × radius³ and a cone is exactly one third of the cylinder with the same base and height. Useful reminder for DIY: one cubic metre equals 1,000 litres.
Everyday examples
For DIY, calculate a wall's area before buying paint: a 5 m by 2.5 m wall is 12.5 m², and a tin covering 10 m² per litre tells you how much you need. For gardening, the volume of a cylindrical planter or round pool follows π × radius² × depth — a pool 3 m in diameter and 1.20 m deep holds about 8.5 m³, or 8,500 litres of water.
In real estate, the habitable surface area of a rectangular room can be checked in seconds, and French law imposes a precise measurement for selling a lot in co-ownership. When moving house, estimating the volume of boxes and furniture — treated as cuboids — helps choose the right van size. In every case, take all measurements in the same unit before entering the values.
Frequently asked questions about area and volume
How do I calculate the area of a room that is not rectangular?
Split it into simple shapes: rectangles, triangles or portions of circles. Calculate the area of each piece and add them together. An L-shaped room is treated as two rectangles, a wall with a triangular gable as a rectangle plus a triangle.
What is the difference between area and surface?
In everyday language the two words mean the same thing: a measurement in square units (m², cm²). In strict geometry, area is the numerical measure and surface is the geometric object itself. On this calculator the words are used interchangeably.
How do I convert a volume in cubic metres to litres?
One cubic metre is exactly 1,000 litres, and one litre is one cubic decimetre. So multiply the volume in m³ by 1,000 to get litres: a 2.4 m³ tank holds 2,400 litres.
What value of π is used in the calculations?
The calculator uses the exact mathematical value of π available in your browser (about 3.141592653589793), far more precise than the 3.14 or 22/7 approximations used in mental arithmetic. The result is then rounded for display.
Can I enter dimensions in centimetres and get a result in metres?
Enter all dimensions in the same unit: the result will be in the corresponding unit (cm² or m² for area, cm³ or m³ for volume). To convert afterwards, use our unit converter, remembering that one square metre equals 10,000 square centimetres.