Area Calculator
Calculate the area of a rectangle, triangle, trapezoid, circle, sector, ellipse or parallelogram — each its own calculator, showing the formula and the working.
Rectangle
Four right angles — a room, a plot, a sheet.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the length and width, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
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- Square Inches
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- Square Yards
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- Square Meters
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- Acres
- —
Check your entries
Changes update automatically.
Triangle
Three sides measured, no angles needed.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the edge 1 and edge 2 and edge 3, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
- —
- Square Inches
- —
- Square Yards
- —
- Square Meters
- —
- Acres
- —
Check your entries
Changes update automatically.
Trapezoid
Two parallel sides and the distance between them.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the base 1 and base 2 and height, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
- —
- Square Inches
- —
- Square Yards
- —
- Square Meters
- —
- Acres
- —
Check your entries
Changes update automatically.
Circle
Measured from the centre out — the radius, not the diameter.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the radius, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
- —
- Square Inches
- —
- Square Yards
- —
- Square Meters
- —
- Acres
- —
Check your entries
Changes update automatically.
Sector
A wedge of a circle, cut by an angle at the centre.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the radius and angle, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
- —
- Square Inches
- —
- Square Yards
- —
- Square Meters
- —
- Acres
- —
Check your entries
Changes update automatically.
Ellipse
A stretched circle — half its width and half its height.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the semi-major axes and semi-minor axes, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
- —
- Square Inches
- —
- Square Yards
- —
- Square Meters
- —
- Acres
- —
Check your entries
Changes update automatically.
Parallelogram
A slanted rectangle — base times perpendicular height.
Example
This is a sample result, not your calculation. Enter your own values to replace it.
Enter the base and height, then calculate the area.
Your measurements were in different units, so each was converted into the first field's unit before the formula ran.
Show result in other units
- Square Feet
- —
- Square Inches
- —
- Square Yards
- —
- Square Meters
- —
- Acres
- —
Check your entries
Changes update automatically.
How to use this calculator
- Find the shape that matches what you are measuring — each one above is its own calculator, so an answer stays on screen while you work out the next.
- Enter each measurement and choose the unit beside it. Every measurement carries its own unit, so a length in feet beside a width in inches is fine.
- Press that shape's Calculate button.
- Read the area, reported in the unit of the first field squared, with the formula and the substituted numbers shown above it.
Area formulas for every shape
Each shape has its own formula, but they all return a result in square units. These are the seven the calculator handles, in the order they appear above:
| Shape | Formula | Example |
|---|---|---|
| Rectangle | length × width | 8 × 5 = 40 |
| Triangle | √(s(s − a)(s − b)(s − c)), s = (a + b + c) ÷ 2 | sides 3, 4, 5 → 6 |
| Trapezoid | ½ × (b1 + b2) × height | ½ × (6 + 4) × 3 = 15 |
| Circle | π × radius2 | π × 52 ≈ 78.54 |
| Sector | (angle ÷ 360) × π × radius2 | 90° of r 5 ≈ 19.63 |
| Ellipse | π × a × b | π × 5 × 3 ≈ 47.12 |
| Parallelogram | base × height | 6 × 4 = 24 |
The triangle works from its three edges, so no angle or height is needed — measure the three sides and Heron's formula does the rest. For the parallelogram, height is the perpendicular distance between the two parallel sides, not the slanted edge. For the ellipse, a and b are the two semi-axes — the distances from the centre to the edge along each direction. A square is just a rectangle with equal sides, so use the rectangle for one.
A worked example
Take a circular patio with a radius of 5 metres. The area is π × radius2 = π × 52 = π × 25 ≈ 78.54 square metres. If you only know the diameter, halve it first — a 10-metre diameter is a 5-metre radius. A trapezoidal garden bed with parallel sides of 6 and 4 and a height of 3 works out to ½ × (6 + 4) × 3 = 15 square units.
Why area is always in squared units
Area measures a two-dimensional surface, so it multiplies one length by another and the units multiply too. Measure in metres and the area is in square metres; measure in feet and it is in square feet. Every measurement must reach the formula in the same unit, since multiplying feet by inches gives a meaningless number — the calculator converts each one into the unit of the first field for you, and says so when your units differ.
Measuring an irregular space
Real rooms and lots are rarely one clean shape. The reliable trick is to split an awkward outline into rectangles, triangles and circle segments, find each area separately, and add them. An L-shaped room, for instance, is just two rectangles. For a piece cut out — a circular pond in a rectangular yard — find both areas and subtract the hole from the whole.
Common mistakes to avoid
- Using diameter instead of radius in a circle. The formula needs the radius; the diameter is twice too big and quadruples the area.
- Using a slanted side as the height of a parallelogram or trapezoid. Height is always measured at a right angle to the base.
- Forgetting which unit the answer is in. It follows the first field, so entering a radius in feet gives square feet even if a later measurement was in inches.
For a floor or room specifically, the square footage calculator also estimates material cost. For 3D shapes, use the volume calculator, and for a triangle from its three side lengths, the triangle calculator finds the area and every angle.
Frequently asked questions
How do I calculate the area of a shape?
It depends on the shape. A rectangle is length × width; a circle is π × radius²; a triangle from three sides uses Heron's formula. Each shape above is its own calculator — use the one that matches what you are measuring, and it shows the formula and the working alongside the answer.
How do I find the area of a circle?
Area = π × r², where r is the radius (half the diameter). For a circle with radius 5, the area is π × 25 ≈ 78.54 square units. If you only know the diameter, halve it first to get the radius.
How do I find the area of a triangle?
The triangle calculator above works from the three side lengths using Heron's formula: take s = (a + b + c) ÷ 2, then the area is √(s(s − a)(s − b)(s − c)). A 3-4-5 triangle gives s = 6 and an area of 6. If you know a base and its perpendicular height instead, the area is simply ½ × base × height.
What is the area of a rectangle?
Length × width. A room 8 units long and 5 wide is 8 × 5 = 40 square units. A square is the special case where length and width are equal, so its area is side².
What units does the area come out in?
Every measurement has its own unit, so you can mix feet and inches freely. Each one is converted into the unit of the first field, and the area is reported in that unit squared — enter a length in metres first and the answer is in square metres.
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About this calculator
Method reviewed for accuracy on July 25, 2026
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