Area Calculator
Pick a shape, enter its measurements and get its area, the amount of flat surface inside it, in square units and converted to mm², cm², m², in², ft² and yd². It finds area only: the distance around a shape is the job of the perimeter calculator, and solving a triangle for its angles belongs to the triangle calculator.
Last updated November 4, 2026
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Result
Area = 40 ft²
| Measure | Value |
|---|---|
| Shape | Rectangle |
| Square ft (ft²) | 40 |
| mm² | 3716121.6 |
| cm² | 37161.216 |
| m² | 3.7161216 |
| in² | 5760 |
| yd² | 4.4444444 |
Area is in square units. Enter every length in the unit chosen, and see the perimeter calculator for the distance around.
Show the work
Formula: A = length × width
- Length 8 ft, width 5 ft.
- A = 8 × 5 = 40 ft².
Result: Area = 40 ft²
Area formulas
rectangle l×w
square s²
triangle ½bh
circle πr²
trapezoid ½(a+b)h
parallelogram bh
ellipse πab
sector (θ/360)πr²
A rectangle is length times width and a square is its side multiplied by itself. A triangle is half of base times height, where the height is measured at a right angle to the base. When you only know the three sides, the calculator uses Heron's formula: with s = (a + b + c) / 2, the area is √(s(s−a)(s−b)(s−c)).
A circle is π times the radius squared, so the diameter is halved first. A trapezoid averages its two parallel sides and multiplies by the height between them. A parallelogram is base times perpendicular height, not base times the slanted side. An ellipse is π times its two semi-axes, which are half of its longest and shortest widths.
A regular polygon with n equal sides of length s has area n × s² / (4 × tan(π / n)). A sector is a slice of a circle: its area is the fraction angle / 360 of the full circle, with the angle in degrees up to 360.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Units and square units
Enter every length in the same unit and choose it from the list. The area comes back in that unit squared and converted to the other five, using exact definitions such as 1 in = 25.4 mm and 1 ft = 0.3048 m. Because area scales with the square of length, 1 yd² is 9 ft², not 3.
Area, perimeter and which tool to use
Area is the surface inside a shape. For the boundary use the perimeter calculator, and the triangle calculator to find missing sides and angles. Choose this page when area is the answer, including sectors, Heron’s formula and unit conversion; the geometry calculator suits a common shape needing perimeter or diagonal too.
How to use the Area Calculator
- Choose the shape. For a triangle, choose base and height or three sides.
- Pick the unit and enter each measurement; for a circle choose radius or diameter first.
- Read the area in your unit and in the five other square units.
- Open Show the work to see the formula with your numbers.
Worked example
A rectangle 8 ft long and 5 ft wide has area 8 × 5 = 40 ft², which is 3.7161216 m² and 4.4444444 yd². The table shows other shapes with all lengths in cm.
| Shape | Measurements | Area (cm²) |
|---|---|---|
| Triangle (Heron) | 13, 14, 15 | 84 |
| Circle | radius 5 | 78.539816 |
| Trapezoid | bases 10 and 6, height 4 | 32 |
| Regular hexagon | side 4 | 41.569219 |
| Sector | radius 6, angle 90° | 28.274334 |
Frequently asked questions
Why is the area in square units?
Area multiplies two lengths, so the unit multiplies too: feet times feet gives square feet. That is why converting 1 square yard gives 9 square feet.
Which height do I use for a triangle or parallelogram?
Use the perpendicular height, measured at a right angle to the base, never the slanted side. If you only know the three sides of a triangle, choose the three-sides option.
Why does it reject my three triangle sides?
Three lengths form a triangle only when each is shorter than the sum of the other two. Sides 1, 2 and 3 fail because 1 + 2 equals 3.