This calculator finds a rectangle's area, perimeter, and diagonal for rooms, materials, and geometry tasks.
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Enter the rectangle's length and width using the same unit. Calculate to get area in square units and perimeter and diagonal in the original length unit.
Area = length × width. Perimeter = 2 × (length + width). Diagonal = square root of (length² + width²).
A patio measuring 15 feet by 8 feet has area 15 × 8 = 120 square feet and perimeter 2 × (15 + 8) = 46 feet. Its diagonal is square root of (15² + 8²) = 17 feet.
The diagonal measures the straight-line distance between opposite corners. Builders also compare the two diagonals to check whether a rectangular frame is square.
No. Swapping length and width does not change the area, perimeter, or diagonal, which is convenient when the labels are unclear.
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