Area Calculator
Last updated: November 4, 2026
Calculate rectangle, triangle, circle or trapezoid area with shape-specific dimension labels.
On this page
Quick summary: Calculate rectangle, triangle, circle or trapezoid area with shape-specific dimension labels.
Read the complete guide
Updated reference sections in this guide are in English.
Using this calculator
Select the shape, then use the labels that appear. Rectangles need length and width; triangles need a base and its perpendicular height; circles need radius; trapezoids need two parallel sides and the perpendicular distance between them. Fields that are not needed for the chosen shape are hidden and ignored.
Calculation method
Triangle: A = base × perpendicular height / 2
Circle: A = π × radius²
Trapezoid: A = (parallel side 1 + parallel side 2) × height / 2
The trapezoid formula uses the average of the two parallel lengths. A triangle’s sloping side is generally not its height. Every dimension must be expressed in one common length unit before calculation; the calculator does not infer a conversion from field names.
Worked examples
Rectangle and triangle
A 5-by-4 rectangle has area 20 square units. A triangle with base 5 and perpendicular height 4 has half that area: 10 square units.
Trapezoid
Parallel sides 5 and 4 with perpendicular height 3 give (5 + 4) × 3 ÷ 2 = 13.5 square units.
Check this scenario in the calculator:
- Shape
- Rectangle
- Length
- 5
- Width
- 4
- Perpendicular height
- 3
Understanding the result
An area in square meters is not interchangeable with square feet. Convert dimensions first or convert the finished area using a squared conversion factor. Scaling every length by two multiplies area by four, which is a useful check when comparing similar shapes.
Boundaries and assumptions
Dimensions must be nonnegative and no larger than 10⁹. A zero dimension may describe a degenerate shape and can give zero area. The form handles ideal simple shapes, not irregular boundaries, cutouts, floor plans with several regions or material waste. Split composite shapes into parts and account for overlaps separately.
Questions and reference
Can I use the triangle’s longest side as height?
Only if that length is actually perpendicular to the selected base. Otherwise it is not the height required by this formula.
Why are some fields hidden?
Each shape has different required dimensions. Hidden dimensions are disabled and do not affect the result.