Circle Area and Circumference Chart
Area and circumference for every diameter from 1 to 40 feet. Area goes with the square of the radius, so doubling the diameter quadruples the material — the reason a slightly wider patio costs so much more concrete.
Source data and formula checked · How we check
Circle Area and Circumference Chart reads area straight off diameter, for 40 values from 1 to 40. Every row is computed from the same formula the calculator uses, not measured or copied from another table, so a value between two rows can be worked out the same way. The formula is the one published by Wolfram MathWorld.
| Diameter (ft) | Area | Circumference |
|---|---|---|
| 1 | 0.79 sq ft | 3.14 ft |
| 2 | 3.14 sq ft | 6.28 ft |
| 3 | 7.07 sq ft | 9.42 ft |
| 4 | 12.57 sq ft | 12.57 ft |
| 5 | 19.63 sq ft | 15.71 ft |
| 6 | 28.27 sq ft | 18.85 ft |
| 7 | 38.48 sq ft | 21.99 ft |
| 8 | 50.27 sq ft | 25.13 ft |
| 9 | 63.62 sq ft | 28.27 ft |
| 10 | 78.54 sq ft | 31.42 ft |
| 11 | 95.03 sq ft | 34.56 ft |
| 12 | 113.10 sq ft | 37.7 ft |
| 13 | 132.73 sq ft | 40.84 ft |
| 14 | 153.94 sq ft | 43.98 ft |
| 15 | 176.71 sq ft | 47.12 ft |
| 16 | 201.06 sq ft | 50.27 ft |
| 17 | 226.98 sq ft | 53.41 ft |
| 18 | 254.47 sq ft | 56.55 ft |
| 19 | 283.53 sq ft | 59.69 ft |
| 20 | 314.16 sq ft | 62.83 ft |
| 21 | 346.36 sq ft | 65.97 ft |
| 22 | 380.13 sq ft | 69.12 ft |
| 23 | 415.48 sq ft | 72.26 ft |
| 24 | 452.39 sq ft | 75.4 ft |
| 25 | 490.87 sq ft | 78.54 ft |
| 26 | 530.93 sq ft | 81.68 ft |
| 27 | 572.56 sq ft | 84.82 ft |
| 28 | 615.75 sq ft | 87.96 ft |
| 29 | 660.52 sq ft | 91.11 ft |
| 30 | 706.86 sq ft | 94.25 ft |
| 31 | 754.77 sq ft | 97.39 ft |
| 32 | 804.25 sq ft | 100.53 ft |
| 33 | 855.30 sq ft | 103.67 ft |
| 34 | 907.92 sq ft | 106.81 ft |
| 35 | 962.11 sq ft | 109.96 ft |
| 36 | 1,017.88 sq ft | 113.1 ft |
| 37 | 1,075.21 sq ft | 116.24 ft |
| 38 | 1,134.11 sq ft | 119.38 ft |
| 39 | 1,194.59 sq ft | 122.52 ft |
| 40 | 1,256.64 sq ft | 125.66 ft |
Questions people actually ask
- How do I read the Circle Area and Circumference Chart?
- Find your diameter in the first column and read across. At 1 ft the area is 0.79 sq ft; at 40 ft it is 1,256.64 sq ft. The table runs from 1 ft to 40 ft in 40 rows.
- Can I read between two rows?
- Not by splitting the difference. The area does not change by the same amount from row to row, so the midpoint of two rows is not the answer for the midpoint of two diameter values. Put the exact figure into the calculator instead — it uses the same formula that produced every row here.
- What if my diameter is outside the table?
- The chart covers 1 ft to 40 ft, which is the range people actually look up. Anything above or below goes into the calculator, which takes any figure and shows each step of the working rather than only the result. Open the circle calculator.
- Where do these numbers come from?
- Every row is computed at build time from the formula published by Wolfram MathWorld, by the same code behind the calculator — not transcribed from another table, which is how a rounding error in one chart ends up in twenty.
Need a different number?
The chart covers the common values. For anything between the rows, the circle calculator takes any figure and shows the working.
Source: Wolfram MathWorld — circle, NIST Digital Library of Mathematical Functions