Geometry Calculator
Geometry problems are mostly about picking the right formula and plugging in the right measurements. This calculator covers the shapes you meet most often in school and everyday jobs, from painting a wall to filling a cylindrical tank. Choose a shape, enter its dimensions, and get area, perimeter or volume.
How to use the geometry calculator
- Choose a shape. The label tells you what a, b and c mean for that shape.
- Enter the dimensions in the same unit. Unused boxes are ignored.
- Read the area or volume. Results are in square or cubic units of whatever you entered.
Formula
- Rectangle: A = ab, P = 2(a+b)
- Triangle: A = ½ab
- Circle: A = πr², C = 2πr
- Trapezoid: A = ½(a+b)c
- Sphere: V = 4/3 πr³, S = 4πr²
- Cylinder: V = πr²h
- Cone: V = ⅓πr²h
- Box: V = abc, S = 2(ab+bc+ac)
Worked examples
Painting a wall
A 5 m by 3 m wall has an area of 15 m². One litre of paint often covers about 10 m², so you need about 1.5 litres per coat.
Water tank
A cylinder with radius 3 and height 10 has volume π × 3² × 10 = 282.74 cubic units.
Choosing and using geometry formulas
Perimeter, area and volume
Perimeter is length, area is a surface and volume is space. That is why their units are metres, square metres and cubic metres. When a length doubles, the perimeter doubles, the area quadruples and the volume becomes eight times larger.
Everyday examples
| Job | Measure | Shape |
|---|---|---|
| Paint a wall | Area | Rectangle |
| Fence a garden | Perimeter | Rectangle / circle |
| Fill a tank | Volume | Cylinder / box |
| Pizza size | Area | Circle |
Why pizza sizes surprise people
Area grows with the square of the radius. A 16-inch pizza has area π × 8² ≈ 201 in², while a 12-inch has π × 6² ≈ 113 in². The larger one is 78% more pizza, not 33% more.
Breaking down complex shapes
An L-shaped room is two rectangles. A running track is a rectangle plus two half circles. Split, calculate and add. For volumes of shapes with a constant cross-section (prisms and cylinders), multiply the base area by the height. A cone or pyramid is one third of that.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- Area of a circle with radius 7.
Show answer
Area: 153.93804
- Volume of a box 6 × 4 × 3.
Show answer
Volume: 72
Common mistakes to avoid
- Using diameter instead of radius. The radius is half the diameter.
- Mixing units, such as centimetres and metres, in one calculation.
- Forgetting that area is in square units and volume in cubic units.
Frequently asked questions
What is the difference between area and perimeter?
Area is the space inside a shape; perimeter is the distance around its edge.
What value of π is used?
The full precision of π (3.14159265…), not just 3.14.
How do I find the area of an irregular shape?
Split it into rectangles, triangles and circles, find each area and add them.
What units does it use?
Any consistent unit. If you enter metres, area is in square metres and volume in cubic metres.
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.