Area Calculator: Area Formula of Rectangle and Other Shapes
Area of a parallelogram formula
A = b × h
Base b · Perpendicular height h
Drop a perpendicular height to cut a triangle from the left corner.
A = b × h
The dissection preserves area. Diagram not to scale; use the labelled measurements.
Worked example you can change
Area = base × perpendicular height
- Area ≈ 40 square units
Calculator
Enter complete decimal numbers using one common unit for dimensions; changing the unit label does not convert numbers. Decimal answers are shown to 15 significant digits.
- Area
- 40 cm²
Formula variants
| Shape or method | Formula | Meaning |
|---|---|---|
| Rectangle | A = length × width | Multiply perpendicular adjacent sides. |
| Square | A = side² | Both side lengths are equal. |
| Triangle | A = base × height ÷ 2 | Use perpendicular height, not a sloping side. |
| Circle | A = πr² | Radius is half the diameter. |
| Trapezoid | A = (a + b)h ÷ 2 | a and b are the parallel sides. |
| Parallelogram | A = bh | Shearing does not change base or perpendicular height. |
| Rhombus | A = d₁d₂ ÷ 2 | Use the two diagonal lengths. |
| Sector | A = (θ/360)πr² | θ is the central angle in degrees. |
Questions
What is the area formula of a rectangle?
Area equals length multiplied by width. An 8 cm by 5 cm rectangle has area 40 cm².
Why is parallelogram area base times height?
Cut the triangle at one end and move it to the other. The pieces form a rectangle with the same base and perpendicular height.
Does changing the unit convert my numbers?
No. The selector labels all dimensions in the same unit; enter converted dimensions yourself.
Sources and method
Find area of rectangle, square, triangle, circle, trapezoid, parallelogram, rhombus or sector. Height is perpendicular to the base.
We calculate with 40 significant digits and round only the displayed result. Diagrams are labelled explanations and are not measurement drawings.
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