What it works out
Square up a room, slab or panel: area, perimeter and the diagonal check from two measurements.
Use this when you know the length and width of a room, slab or panel. Enter both and you get the area, the perimeter and the corner to corner diagonal. The diagonal is your square check: lay out the shape, measure both diagonals, and if they match the corners are square. Results use your own units and rounding settings.
The formula
- Area
- length × width
- Perimeter
- 2 × (length + width)
- Diagonal
- √(length² + width²)
In words: Area = length times width; perimeter = 2 times (length plus width); diagonal = the square root of length squared plus width squared
Worked example
A room 12 ft by 8 ft
- Length 12 ft
- Width 8 ft
- Area = 12 × 8 = 96 ft²
- Perimeter = 2 × (12 + 8) = 40 ft
- Diagonal = √(12² + 8²) = √208 = 14.42 ft
Both diagonals should measure about 14.42 ft when the corners are square.
Good to know
- Rectangles only: for other shapes, split them into rectangles and triangles.
- Results follow your units and rounding settings.
- A calculator, not a building-code check: confirm local rules with your building authority.
Questions
How do I check a layout is square?
Measure both corner to corner diagonals. If they are equal, and opposite sides are equal, the corners are square.
Does it add waste?
No. It is pure geometry. Use a materials tool when you need an order quantity.