Calculate area in square metres for rectangles, triangles, circles, and trapezoids
The square metre is the standard unit of area measurement used in the UK and internationally. Whether you are measuring a room for new flooring, calculating garden area for turf or paving, or working out the area of an irregularly shaped plot, knowing the area in square metres is essential for ordering the right amount of materials and getting accurate quotes from tradespeople. This calculator supports four common shapes: rectangles (including squares), triangles, circles, and trapezoids. For each shape, it calculates the area in square metres and automatically converts to square feet, which is still widely used in UK property listings and by some tradespeople. It also calculates the perimeter, which is useful for fencing, skirting boards, edging, and other linear materials. Many people struggle with area calculations for anything beyond a simple rectangle. Triangular areas occur in loft spaces, gable ends, and irregular gardens. Circular areas come up with ponds, patios, and roundabouts. Trapezoids are common in gardens that narrow at one end. This calculator handles all these shapes with a simple input interface.
To calculate area in square metres: 1. Select the shape you want to measure. Choose from rectangle, triangle, circle, or trapezoid. 2. For a rectangle or square, enter the length and width in metres. For a square, these will be the same value. 3. For a triangle, enter the base (length) and height (width) in metres. The height must be perpendicular to the base, not the length of a side. 4. For a circle, enter the radius in metres. The radius is half the diameter. If you know the diameter, divide by 2 first. 5. For a trapezoid, enter the two parallel sides (side A and side B) and the height (width/distance between them) in metres. 6. View the results. The area is shown in both square metres and square feet, along with the perimeter in metres. 7. To measure a room, measure the longest wall and the wall perpendicular to it at their widest points. For L-shaped rooms, divide into two rectangles and calculate each separately.
The area formulas used for each shape are: Rectangle: area = length x width. Perimeter = 2 x (length + width). Triangle: area = 0.5 x base x height. The base is any side and the height is the perpendicular distance from that side to the opposite vertex. Circle: area = pi x radius squared. Perimeter (circumference) = 2 x pi x radius. Trapezoid: area = (side A + side B) / 2 x height, where side A and side B are the two parallel sides and the height is the perpendicular distance between them. The conversion from square metres to square feet uses the factor 10.7639. For example, a 5m x 3m rectangle has an area of 15 square metres, which equals 15 x 10.7639 = 161.46 square feet. Perimeter for the trapezoid assumes equal non-parallel sides (an isosceles trapezoid) calculated using Pythagoras: side length = sqrt(((sideA - sideB) / 2) squared + height squared).
When measuring for materials, always add a waste allowance. For flooring, add 5-10% for cuts and offcuts. For paint, use the area to calculate coverage (a typical emulsion covers about 12 square metres per litre). For turf, add 5% for trimming. Estate agents in the UK measure property area using the RICS Code of Measuring Practice, which may differ from a simple length-by-width measurement because it includes or excludes certain areas like bay windows, staircases, and built-in wardrobes.