Geometry Calculator
Select a shape and enter measurements.
About this calculator
Choose a shape, enter its measurements and get the area, perimeter or circumference, and for solids the surface area and volume. Shapes include circle, rectangle, triangle, trapezoid, sphere, cylinder, cone, cube and cuboid.
Formulas are shown with each result so you can learn them, not just use them.
How to use it
- Pick the Shape.
- Enter the measurements, such as radius, length, width or height.
- Read the area, perimeter and volume results.
Core formulas
Circle: A = πr², C = 2πr. Rectangle: A = lw. Triangle: A = ½bh. Trapezoid: A = ½(a + b)h. Sphere: V = 4/3 πr³, S = 4πr². Cylinder: V = πr²h. Cone: V = ⅓πr²h. Cube: V = a³. Cuboid: V = lwh.
Worked example
Circle, radius 5
| Area | 78.5398 |
| Circumference | 31.4159 |
| Sphere of radius 5, volume | 523.599 |
| Cylinder r = 5, h = 10, volume | 785.398 |
Tips and common mistakes
- Use the same unit for all measurements. Area comes out in square units and volume in cubic units.
- Diameter is twice the radius; halve it before using the formulas.
- For a triangle, the height is perpendicular to the base.
- Use π = 3.14159 or the calculator's π for accuracy.
- Check shapes with simple numbers, such as a 1 × 1 square having area 1.
Frequently asked questions
What is the area of a circle?
πr², where r is the radius.
What is the volume of a cylinder?
πr²h.
What is the circumference?
The distance around a circle: 2πr.
How do I find a triangle's area?
Half the base times the height.
What is the volume of a sphere?
4/3 πr³.
What units do results use?
Square units for area, cubic units for volume.