Area calculator: choose a flat shape, enter dimensions in one consistent unit, and calculate its area locally. The result shows the formula used, the entered dimensions, and the answer in square units.
Area Calculator
LiveHow the area calculator works
Area measures the two-dimensional surface a shape covers. The National Institute of Standards and Technology describes area in square units and identifies the square meter as the SI derived unit. That is why a length entered in meters produces an answer in meters squared, while a length entered in feet produces an answer in feet squared.
For a rectangle 6 m long and 4 m wide, multiply 6 by 4. The area is 24 m squared. For a circle with radius 5 m, multiply pi by 5 by 5 to get approximately 78.539816 m squared.
Which dimensions belong in each formula?
| Shape | Dimensions to enter | Important check |
|---|---|---|
| Square | One side | All sides must have the same length. |
| Rectangle | Length and width | Both measurements use the same unit. |
| Circle | Radius | Radius is half of diameter; do not enter the full diameter as radius. |
| Triangle | Base and perpendicular height | The height must meet the chosen base at a right angle. |
| Trapezoid | Two parallel bases and perpendicular height | Use the parallel sides, not the sloped edges, as the two bases. |
Area, surface area, and volume are different
| Question | Use | Reason |
|---|---|---|
| How much flat floor, paper, lawn, or wall face is covered? | This Area Calculator | It measures one two-dimensional shape. |
| How much material covers the outside of a box, sphere, or cylinder? | Surface Area Calculator | It adds the outer faces of a three-dimensional object. |
| How much space is inside a box, tank, or solid? | Volume Calculator | It measures three-dimensional capacity rather than a flat surface. |
| How do I express an existing area in another unit? | Area Converter | It converts a finished area result instead of recalculating a shape. |
Important limits before using the result
Step-by-step method
- Select the shape that matches the flat surface being measured.
- Choose a dimension unit and use it consistently for every input.
- Enter the required dimensions, including a perpendicular height for a triangle or trapezoid.
- Read the result in square units and use Area Converter only if the completed area must be expressed in another unit.
Frequently asked questions
What unit will the area answer use?
The answer uses the dimension unit squared. If every dimension is in m, the result is m squared. If every dimension is in ft, the result is ft squared. Keep every entered dimension in the same unit.
Do I enter radius or diameter for a circle?
Enter radius. Radius runs from the center to the circle edge and equals half the diameter. If all you know is diameter, divide it by 2 first.
Can this calculate an irregular area?
Not from one set of dimensions. Split the outline into regular pieces you can measure, calculate each piece, subtract any cut-outs, and add the remaining areas.
Why is area not the same as volume?
Area measures a flat surface with two dimensions. Volume measures enclosed space with three dimensions. A room floor has area; the air inside the room has volume.
Does the calculator send my dimensions anywhere?
No. The selected shape, dimensions, result cards, and diagram update locally in the browser.
Sources
- National Institute of Standards and Technology: SI Units - Area - definition of area as two-dimensional surface coverage, square units, and the square meter as the SI derived unit.
- National Institute of Standards and Technology: Guide to the SI, Appendix B.8 - published conversion-factor context for area-related units such as acre and hectare.
Related calculators
See the full list of Math calculators, or try:
- Area Converter - express a completed area result in another area unit
- Circle Calculator - work with radius, diameter, circumference, and circle area together
- Triangle Calculator - calculate triangle dimensions and related measurements in more detail
- Surface Area Calculator - find the outside area of a three-dimensional object
- Volume Calculator - calculate the internal capacity of a three-dimensional shape