OnlineCalculator360
Result
How the Calculator Works
Enter the radius of your circle and select your unit. The calculator applies A = πr² and returns the area in square units, plus the circumference for reference. There is no intermediate step to manage; the formula display at the bottom shows the substituted values so you can verify the result at a glance.
The most common mistake people make is entering the diameter when they mean the radius. The radius is the distance from the exact centre to any point on the edge. If you have measured across the full circle, halve that number before entering it.
The Formula and a Worked Example
Circumference = 2 × π × r
where r = radius and π ≈ 3.14159
A raised garden bed on a terrace is circular with a diameter of 2.4 m.
Radius = 2.4 ÷ 2 = 1.2 m
Area = π × (1.2)² = 3.14159 × 1.44 = 4.52 m²
Circumference = 2 × π × 1.2 = 7.54 m
At a planting density of 6 plants per m², this bed can hold about 27 plants. The circumference tells you how much edging material to buy: 7.54 m, rounded up to 8 m with a small overlap.
Where Area Calculations Actually Matter
Circular area calculations come up more often than people expect in everyday home and garden planning. Here are the most practical scenarios:
| Situation | What You Measure | Why Area Matters |
|---|---|---|
| Round dining table | Table diameter | How many place settings fit; whether a round rug underneath works |
| Overhead water tank (top view) | Tank diameter | Cross-section area x height gives tank volume in litres |
| Circular raised garden bed | Bed diameter | Soil volume, plant count, edging material length |
| Lawn sprinkler head | Spray throw radius | Coverage zone per head; number of heads for full coverage |
| Circular floor decal or rug | Decal/rug diameter | Wall-to-wall clearance in the room |
| Cylindrical water sump | Inner diameter | Base area x depth = total storage capacity |
Tank Volume from Area
A very common Indian household use: if your overhead tank has an inner diameter of 1.0 m and is 1.5 m tall, the cross-section area is π × 0.25 = 0.785 m². Multiply by height: 0.785 × 1.5 = 1.178 m³ = approximately 1,178 litres. Most 1,000-litre tanks have a diameter around 0.9 to 1.0 m for this reason.
Working from Diameter, Circumference, or Area
Sometimes you have a measurement other than the radius. Here is how to convert before entering into the calculator:
| You know | Formula for radius | Example |
|---|---|---|
| Diameter (d) | r = d ÷ 2 | 60 cm diameter → r = 30 cm |
| Circumference (C) | r = C ÷ (2π) | C = 188.5 cm → r = 188.5 ÷ 6.283 = 30 cm |
| Area (A) | r = √(A ÷ π) | A = 2827 cm² → r = √(900) = 30 cm |
If you are measuring a real object, stretch a tape across the widest point to get the diameter, then halve it. For curved objects like a pot or drum where the tape slips, wrap a string around the widest rim to get the circumference, then use the formula above.
Frequently Asked Questions
Area = π × r², where π ≈ 3.14159 and r is the radius. A circle with a 3 m radius has an area of 3.14159 × 9 = 28.27 m².
Divide the diameter by 2 to get the radius, then apply A = πr². A circular table 1.2 m across has radius 0.6 m and area π × 0.36 = 1.13 m².
No. Circumference is the perimeter length of the circle (2πr), measured in linear units like metres. Area is the flat surface enclosed inside the circle (πr²), measured in square units like m².
Measure from centre to edge to get the radius. A raised bed with 1.5 m radius covers π × 2.25 = 7.07 m². Multiply by bed depth to get the soil volume needed.
A circle always encloses more area. For a 12 m perimeter: the circle (radius 1.91 m) has area 11.46 m², while a square (3 m side) has area 9 m². Circular designs are more space-efficient for the same boundary length.
Area is in square units matching your input. Metres input gives m² output; centimetres gives cm². Circumference is in the same linear unit as the radius you entered.
Calculate area with A = πr², then multiply by depth. A 1 m radius bed that is 0.3 m deep needs π × 1 × 0.3 = 0.94 m³ of soil, roughly 940 litres or about 18 standard 50-litre bags.
Yes. If a sprinkler throws water up to 4 m, its coverage is π × 16 = 50.3 m². Divide your total lawn area by 50.3 to find the minimum number of heads needed, then add 15% overlap for even coverage.