Area Calculator
This area calculator handles every common flat shape in one place. Pick a rectangle, square, triangle, circle, trapezoid, parallelogram, or regular polygon, type in the dimensions, and you'll get the area right away, with the formula shown and the answer in square inches, square feet, square meters, and acres. It's the quick way to compute area without hunting down a different formula for each shape.
- 7 shapes in one tool
- Formula shown
- Square feet, meters, acres
- Perimeter too
- Live diagram
Last updated June 16, 2026 Covers 7 shapes Reviewed by the Calcowa math team
Enter positive numbers to see the area.
Show all area units
A = l × w
What is area?
Area is the amount of flat surface a shape covers, measured in square units. If you imagine tiling a shape with little squares, the area is how many squares it takes to fill it. That's why a square 3 inches on each side has an area of 9 square inches, not 12. Area always uses squares because a flat shape spreads in two directions at once: length and width.
Perimeter is the distance around the edge, measured in plain length units, while area is the space inside, measured in square units. Land area gets reported in acres or hectares, but those are just larger square measures for big plots.
Area formula for each shape
There isn't one area formula that fits every shape, so here's the area formula for the seven shapes this tool covers. The circle row opens its own calculator with extra options.
| Shape | Formula | In words |
|---|---|---|
| Rectangle | A = l × w | Length times width |
| Square | A = s² | Side squared |
| Triangle | A = ½ b h | Half the base times the height |
| Circle | A = π r² | Pi times the radius squared |
| Trapezoid | A = ½ (a + b) h | Average of the parallel sides times height |
| Parallelogram | A = b × h | Base times the straight height |
| Regular polygon | A = ¼ n s² cot(π/n) | From the number of sides and side length |
How do you calculate area and perimeter?
To calculate area, match your shape, measure it, and apply that shape's formula. The perimeter is the distance around the edge, so you'll add up the side lengths. Here's the routine:
- 1
Pick the matching shapeA room is a rectangle, a gable is a triangle, a pond might be a circle.
- 2
Measure in one unitMeasure every side or radius in the same unit so the math lines up.
- 3
Apply the area formulaMultiply the dimensions with the shape's formula above to get the area.
- 4
Add the sides for perimeterFor the distance around, add up the edge lengths, or use 2(l + w) for a rectangle.
Area in square feet, meters, and acres
Once you've got the area in square units, switching to square feet, square meters, or acres is one more step, and this calculator shows them all. One square foot is 144 square inches, one square meter is about 10.76 square feet, and one acre is 43,560 square feet. So if you measure a room in feet and inches, you'll still get a clean square-foot total. For land, the acres and hectares figures are usually what you'll want.
Land area and plot area
For a plot that's roughly four-sided and close to a rectangle, multiply the length by the width and read the acres or hectares from the result. A lot 100 by 150 feet is 15,000 square feet, and that's about 0.34 acres. For oddly shaped land, surveyors lean on map and GPS area tools, but the rectangle and triangle formulas here cover most regular plots, and you can split a four-sided lot into two triangles when the corners aren't square.
How to find the area of an irregular shape
Not every surface is a tidy rectangle or circle. For an irregular shape, the trick is to split it into shapes you recognize, work out each area, and add them together. A garden might break into a rectangle plus a half circle at one end. There's no single formula for a truly irregular area, so splitting it into familiar pieces is the dependable approach, and you can use the tool above for each piece.
Area units and accuracy
Calcowa shows the area in square millimeters through square miles, plus acres and hectares, all at once. The math uses the full value of pi for the circle, so it's accurate for flooring, paint, gardening, land, and school work alike.
| Unit | Best for | Good to know |
|---|---|---|
| Square inches (in²) | Small parts, fabric | Default when you enter inches |
| Square feet (ft²) | Rooms, flooring, paint | 1 ft² = 144 in² |
| Square meters (m²) | Walls, land, plans | 1 m² = 10.76 ft² |
| Acres | Land and plots | 1 acre = 43,560 ft² |
| Hectares (ha) | Farm and large land | 1 ha = 10,000 m² |
Frequently asked questions
What's the difference between area and surface area?
Area is for flat shapes, the kind on this page. Surface area is the total of all the faces of a 3D solid, like a box or a ball. For those, see the surface area calculators in the geometry hub.
Match your shape, then apply its formula. A rectangle is length times width, a triangle is half the base times the height, and a circle is pi times the radius squared. The calculator above computes the area for seven shapes the moment you type the numbers in.
Each shape has its own area formula. A square is s², a rectangle is l × w, a triangle is ½ b h, a circle is π r², and a trapezoid is ½ (a + b) h. The table on this page lists every formula side by side so you can pick the right one.
Multiply pi by the radius squared: A = π r². For a radius of 5 inches, that's about 78.5 square inches. Pick Circle above, or open the full area of a circle calculator for semicircle, quarter, and sector areas.
Split it into shapes you recognize, find the area of each part, and add them up. A backyard might break into a rectangle plus a triangle. There's no single formula for an irregular shape, so the split-and-add method is the reliable way to handle it.
For a four-sided plot that's close to a rectangle, multiply the length by the width, then convert to acres or hectares, which this tool shows for you. Surveyors use map and GPS tools for odd-shaped land, but for a regular plot the rectangle or triangle formula gets you there.
No. Body surface area is a medical estimate of a person's skin area from height and weight, not a geometry shape. This page handles flat shapes like rectangles and circles. A body surface area tool uses a different formula entirely.
Yes. Area covers a flat surface in two directions, so it's measured in square units like square feet or square meters. Acres and hectares are square measures too, just sized for land.
Area and surface area tools
Need the area of one shape in depth, or the surface area of a solid? These pair well with the area calculator.
Circle, semicircle, quarter, sector.
CircumferenceThe distance around a circle.
Volume calculatorSpace inside a 3D shape.
Cylinder surface areaTotal area of a can or pipe.
Sphere surface areaThe skin of a ball.
CubeSurface area and volume in one.
Need a different shape?
Switch shapes in the tool above, or browse the full geometry hub.