Area and Volume Formulas Made Simple
The essential area, perimeter and volume formulas for circles, rectangles, triangles, spheres and cylinders — what they mean, how to handle composite shapes, and how to keep units straight.
Circle Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Area
153.9380
- Circumference
- 43.9823
- Diameter
- 14.0000
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Circle Calculator
The Circle Calculator works out your area, along with 2 related figures in an instant. Enter radius and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the radius.
- Read off your area, together with circumference and diameter — the calculator updates automatically, with no button to press.
Formula
The Circle Calculator uses the formula:
Area = 3.141592653589793 × Radius ^ 2
Worked example
For example, with radius of 7 units, the area is 153.9380.
| Radius | 7 units |
|---|
| Area | 153.9380 |
|---|---|
| Circumference | 43.9823 |
| Diameter | 14.0000 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Circumference
- The distance around the edge of a circle, equal to 2 × π × radius.
- Diameter
- The distance across a circle through its centre — twice the radius.
- Radius
- The distance from the centre of a circle or sphere to its edge.
- Area
- The amount of two-dimensional space a shape covers, measured in square units.
Frequently asked questions
Multiply pi (about 3.14159) by the radius squared: A = πr². For a radius of 7, the area is π × 49 ≈ 153.94 square units.
The circumference is the distance around the circle, found with C = 2πr. For a radius of 7 it is about 43.98 units.
The radius runs from the centre to the edge; the diameter runs all the way across through the centre and is twice the radius.
Any consistent unit. The area comes out in those units squared and the circumference and diameter in the same units you entered the radius in.
The Circle Calculator uses the formula: Area = 3.141592653589793 × Radius ^ 2. For example, with radius of 7 units, the area is 153.9380.
Enter the radius. Read off your area, together with circumference and diameter — the calculator updates automatically, with no button to press.
Related guides
Circle Table: Area by Radius
Reference table of area for Circle across a range of radius values — exact, engine-computed figures you can read off at a glance.
How to Calculate Circle: Formula, Steps & Examples
Learn how to calculate Circle — the formula explained step by step, with worked examples and a free calculator to check your answer.