Mode
Dimensions
Your Results
Results are also pinned to the bottom of your screen.Rectangle Properties
Area
60
square units
Perimeter
32
units
Formulas Used
Area = length × width = 10 × 6 = 60Perimeter = 2 × (length + width) = 32Diagonal = √(length² + width²) = √(100 + 36) = 11.6619
Quick Answer
To calculate rectangle properties: Area = length x width. Perimeter = 2 x (length + width). Diagonal = sqrt(length^2 + width^2). For a 10 x 6 rectangle: Area = 60 square units, Perimeter = 32 units, Diagonal = sqrt(136) = 11.66 units. A rectangle is square (90-degree corners) when its measured diagonal equals the computed diagonal — the 3-4-5 rule.
Key Facts
- Formula: Area = length x width
- Formula: Perimeter = 2 x (length + width)
- Formula: Diagonal = sqrt(length^2 + width^2) (Pythagorean theorem)
- A 3 x 4 rectangle has area 12, perimeter 14, and diagonal exactly 5
- The 3-4-5 rule verifies a right angle: 3^2 + 4^2 = 5^2
- Doubling both length and width multiplies area by 4 but perimeter by only 2
- Squares are rectangles with length = width
Frequently Asked Questions
How do I calculate the area of a rectangle?
Multiply length by width: Area = length x width. For example, a rectangle 10 units long and 6 units wide has an area of 60 square units. Make sure both measurements use the same unit before multiplying.
How do I find the diagonal of a rectangle?
Use the Pythagorean theorem: Diagonal = sqrt(length^2 + width^2). For a 3 x 4 rectangle, the diagonal is sqrt(9 + 16) = 5. The diagonal is always longer than both sides and splits the rectangle into two right triangles.
What is the 3-4-5 rule?
The 3-4-5 rule is a practical check for square corners based on the Pythagorean theorem. Measure 3 units along one side and 4 along the adjacent side; the diagonal between those points must be exactly 5. Builders scale it up (6-8-10, 9-12-15) for layout work.
Is a square a rectangle?
Yes. A square is a special rectangle where length equals width. Every formula on this page works for squares: a square with side s has area s^2, perimeter 4s, and diagonal s x sqrt(2).
How do I check if a corner is square?
Enter your length and width, then switch to "Verify with Diagonal" and enter the diagonal you measured with a tape. If it matches the computed diagonal (within tolerance), the corner is square. If not, the sides are out of square and need adjustment.
What units does the calculator use?
Any consistent unit — feet, meters, inches, or centimeters. The results carry the same unit: lengths in units, area in square units. For mixed units, convert first (for example, 6 inches = 0.5 feet).