OnlineCalculator360
Result
On This Page
What This Calculator Covers
The Rectangle Calculator finds the area, perimeter, and diagonal of any rectangle in a single step. Enter the length and width in any unit and all three measurements are returned together with the formula used for each.
Most geometry tools make you calculate these separately. This tool combines all three because they are typically needed together. When measuring a room, you need the area for flooring, the perimeter for skirting boards or paint, and the diagonal to check if the room is square during construction. Running three separate calculations also introduces errors at each step. Getting all three at once from a single pair of inputs eliminates that risk.
The Three Formulas
The diagonal formula comes directly from the Pythagorean theorem: a rectangle's diagonal is the hypotenuse of the right triangle formed by the two sides. The diagonal is always longer than either side but shorter than the sum of both sides.
Example: A bedroom measuring 4.5 m x 3.2 m
Area = 4.5 × 3.2 = 14.4 m² (flooring material needed)
Perimeter = 2 × (4.5 + 3.2) = 2 × 7.7 = 15.4 m (skirting board or wall measurement)
Diagonal = √(4.5² + 3.2²) = √(20.25 + 10.24) = √30.49 = 5.52 m (squareness check)
The calculator handles all three automatically. The formulas are shown here for transparency.
Using This for Rooms and Plots
Room Flooring and Tiling
The area in square metres is the starting figure for ordering flooring materials. For tiles, divide the room area by the area of a single tile and add 10% for cuts, corners, and breakage. A 14.4 m² room using 60 cm x 60 cm tiles (0.36 m² each) needs 14.4 ÷ 0.36 = 40 tiles, plus 4 extras for wastage, giving 44 tiles to order. For laminate or vinyl in square metres, order the area plus the same 10% buffer.
Wall Paint Estimation
To estimate paint, you need the wall area, not the floor area. Measure each wall as a rectangle (width x height), add the four totals, subtract door and window areas (typically 2 m² per door and 1.5 m² per window), then divide by the coverage on the paint tin (usually 10 to 12 m² per litre). The perimeter output here gives you the total width of all four walls, which you multiply by ceiling height to get a quick starting estimate.
Plot of Land
For a rectangular residential plot, the area in square metres or square feet is what property listings use. A 30 ft x 40 ft plot has an area of 1,200 sq ft, which is approximately 111.5 m². The perimeter gives the total fencing or boundary wall length needed. The diagonal is useful during layout to verify that a plot marked as rectangular actually has right angles at all four corners: if the measured diagonal matches the calculated value, the corners are true right angles.
Sports Courts and Outdoor Spaces
A standard badminton court is 13.4 m x 6.1 m: area 81.74 m², perimeter 39 m. A five-a-side football pitch typically runs 40 m x 25 m: area 1,000 m², perimeter 130 m. Both figures are needed when costing synthetic turf, boundary netting, or line marking.
Unit Guide and Conversions
Enter both dimensions in the same unit. The area result will be in square units of that measurement.
| If you enter in | Area result is in | Common use |
|---|---|---|
| Metres (m) | Square metres (m²) | Room flooring, plots, sports courts |
| Centimetres (cm) | Square centimetres (cm²) | Furniture, smaller objects, craft projects |
| Feet (ft) | Square feet (sq ft) | Property listings, US and India real estate |
| Inches (in) | Square inches (sq in) | Tiles, screens, small surfaces |
To convert between units after calculating: 1 m² = 10.764 sq ft. So a 14.4 m² room is approximately 155 sq ft.