Quick start
- Choose rectangle, triangle, circle, trapezoid, or parallelogram.
- Enter the measurements for that exact shape, such as length and width or radius.
- Use one unit for every length, like feet, inches, meters, or centimeters.
- Press Calculate area, then check the formula step before copying the result.
Best uses
Start here if one of these sounds like your job. The examples below show which inputs matter most.
- Find the area of a room, drawing, garden bed, or school geometry shape.
- Compare rectangle, triangle, circle, trapezoid, and parallelogram area without changing tools.
- Check answers in square units before using a result in notes, homework, or a project list.
- See the formula step so you can spot a wrong unit, radius, base, or height.
Choosing the right shape mode
Use rectangle mode for length times width. Use triangle mode when you know the base and the straight height. Use circle mode when you know the radius.
Use trapezoid mode when two sides are parallel and you know both bases plus the height. Use parallelogram mode when you know the base and straight height.
Square units
Area is reported in square units because it measures a flat surface. A 12 ft by 8 ft rectangle is 96 ft^2, not 96 ft.
Do not mix feet and inches, or meters and centimeters, in the same calculation unless you convert first. The calculator does not guess which unit you meant.
Example: a room and a trapezoid bed
For a simple room, choose rectangle and enter 12 ft for length and 8 ft for width. The result is 96 ft^2 because 12 x 8 = 96.
For a trapezoid garden bed with bases of 8 ft and 14 ft and a height of 5 ft, the result is 55 ft^2 because (8 + 14) x 5 / 2 = 55.
Mistakes to check before trusting the answer
For triangles and parallelograms, height means the straight up-and-down distance from the base, not the slanted side.
For circles, enter radius. If you measured across the whole circle, divide that diameter by 2 first.
- For odd floor plans, split the shape into smaller rectangles, triangles, or trapezoids and add the areas.
- For paint, flooring, tile, or material orders, use the project-specific calculator when waste, coverage, or product labels matter.
When to use another tool
Use the Circle Calculator if you want radius, diameter, circumference, and area together.
Use the Square Footage Calculator for room-style flooring jobs, or the Volume Calculator and Surface Area Calculator for three-dimensional solid shapes.
Sources used for this guide
The calculator uses standard flat-shape geometry formulas and square-unit labels. These sources are useful if you want to compare the formula list or unit wording.
Worked examples for Area Calculator
96 ft^2
30 in^2
78.5398163397 ft^2
55 ft^2
FAQ in plain language
Which shapes are supported?
The Area Calculator supports rectangle, triangle, circle, trapezoid, and parallelogram modes.
Is area the same as perimeter?
No. Area measures the flat space inside a shape, such as 96 ft^2. Perimeter measures the distance around the outside edge.
What do the main Area Calculator inputs mean?
The main inputs are the numbers, operation, mode, or known values the calculator needs. Keep units consistent, enter percentages the way the page label shows, and use the examples as a quick check before trusting the answer.
How should I read the Area Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the Area Calculator?
Check units, signs, rounding, and the selected mode before copying the answer. If the number feels weird, rerun one of the examples first, then put your own values back in slowly.
What formula does triangle area use?
Triangle area uses A = base x height / 2. Use the height that drops straight to the base, not a slanted side.
Should I enter circle radius or diameter?
Enter radius. If you measured diameter, divide it by 2 first. A 10 ft diameter circle has a 5 ft radius.
Related tools
- Square Footage Calculator Calculate square feet, square yards, and square meters from length, width, and quantity.
- Circle Calculator Find radius, diameter, circumference, and area from one circle measurement.
- Surface Area Calculator Calculate surface area for boxes, cubes, cylinders, spheres, and cones.
Keep exploring
If this guide is close but not exact, these links keep you near the same kind of problem.
- Calculators Browse the full category for related tools that help with the same job.
- All free tools Search the complete Access Free Tools library by task, category, or tool name.
- All calculator and utility guides Find more plain-language examples, formulas, mistakes, and result explanations.
- Free calculator resources Start here when you are not sure which calculator page fits.
Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.