Circle Calculator
With diameter 12 ft, circle comes to 113.10 sq ft — area. It is reached in 5 steps, the last of which is pi * pow(6, 2), and each one is printed on the page with its numbers filled in. The formula is the one published by Wolfram MathWorld, not an approximation fitted to it.
Area, circumference and radius of a circle from its diameter — in square feet and square inches.
Formula and sources checked · How we check
Diameter 12 ft
113.10 sq ft
Area for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- Radius
12 / 26 ft- Area
pi * pow(6, 2)113.097 sq ft- Circumference
pi * 1237.699 ft- Area in square inches
113.09734 * 14416,286.016 sq in- Side of a square with the same area
sqrt(113.09734)10.635 ft
Several at once
A job is rarely one of anything. Work out the first, add it, change the figures and add the next — the list keeps what each line was, and totals them.
Ask about this in the chatCircle Area and Circumference Chart
Worked example
A 12 ft circle is 113.10 sq ft with a 37.70 ft circumference. Doubling the diameter to 24 ft quadruples the area to 452 sq ft — area scales with the square, which is why a slightly larger patio costs so much more concrete.
How to work it out yourself
- 1.Measure straight across the widest point for the diameter, or double the radius if that is what you have.
- 2.Halve the diameter for the radius, then multiply π by the radius squared.
- 3.Multiply by 144 for square inches, or divide by 10.764 for square meters.
- 4.For the circumference, multiply π by the diameter — useful when only a tape around the object is possible.
Area and circumference by diameter
| Diameter (ft) | Area | Circumference |
|---|---|---|
| 2 | 3.14 sq ft | 6.28 ft |
| 4 | 12.57 sq ft | 12.57 ft |
| 6 | 28.27 sq ft | 18.85 ft |
| 8 | 50.27 sq ft | 25.13 ft |
| 10 | 78.54 sq ft | 31.42 ft |
| 12 | 113.10 sq ft | 37.7 ft |
| 16 | 201.06 sq ft | 50.27 ft |
| 20 | 314.16 sq ft | 62.83 ft |
| 24 | 452.39 sq ft | 75.4 ft |
Diameter in feet. Doubling the diameter quadruples the area — area scales with the square.
The formula
- Radius
12 / 2 - Area
pi * pow(6, 2) - Circumference
pi * 12 - Area in square inches
113.09734 * 144 - Side of a square with the same area
sqrt(113.09734)
Source: Wolfram MathWorld — circle, NIST Digital Library of Mathematical Functions
Questions people actually ask
- Why does doubling the diameter quadruple the area?
- Area depends on radius squared. Double the radius and you square the doubling: 2² = 4. The same rule explains why a 16 in pizza is 78% more food than a 12 in, not 33% more.
- How do I order material for a round patio?
- Use the area here, then run it through the concrete or gravel calculator as if it were the length × width figure. Add a little extra waste — circular forms produce more offcut than rectangular ones.
- What if I only know the circumference?
- Divide it by π (3.14159) to get the diameter, then enter that. A 37.7 ft tape around a tree means a 12 ft diameter.
Related
- Square Footage CalculatorSquare footage of a room, wall, border, gable end, ring or triangle from feet-and-inches measurements, with a waste factor and the cost.
- Tank & Cylinder Volume CalculatorVolume of a cylinder in cubic feet, US gallons and liters — round tanks, pools, culverts and post holes.
- Cone Volume CalculatorVolume of a cone from its diameter and height, in cubic feet, cubic inches and gallons, with the radius and the base area shown separately.
- Sphere Volume CalculatorVolume and surface area of a sphere from its diameter, in cubic feet, cubic inches and gallons, with the radius shown as its own step.
- Circumference CalculatorCircumference of a circle from its diameter or the other way round, with the radius, the area and the arc of one degree shown alongside.
- Arc Length and Sector Area CalculatorArc length, sector area, chord and sector perimeter from a radius and an angle, with the fraction of the full circle shown as its own step.
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