BUILDING & PLANNING · FIELD TOOL
Area of a circle = π × r², where r is the radius. A circle with a 1.5 m radius has an area of 3.1416 × 1.5² = 7.07 m². From the diameter, halve it first; from the circumference, r = C ÷ 2π. A 3 m diameter round slab is therefore 7.07 m² as well.
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| Radius | 1.5 m |
| Diameter | 3 m |
| Circumference | 9.4248 m |
| Area in ft² | 76.09 ft² |
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A = π × r² (or π × d² ÷ 4)
C = 2 × π × r (or π × d)
r = d ÷ 2 = C ÷ 2πA round patio 3 m across:
| Diameter | Area (m²) | Diameter | Area (ft²) |
|---|---|---|---|
| 0.5 m | 0.196 | 2 ft | 3.14 |
| 1 m | 0.785 | 4 ft | 12.57 |
| 2 m | 3.142 | 6 ft | 28.27 |
| 3 m | 7.069 | 10 ft | 78.54 |
| 5 m | 19.63 | 12 ft | 113.1 |
| 10 m | 78.54 | 20 ft | 314.2 |
A = π × r², with π about 3.1416 and r the radius. For r = 1.5 m: 3.1416 × 2.25 = 7.07 m².
Halve the diameter to get the radius, then use π × r². Or use A = π × d² ÷ 4: a 3 m circle is 3.1416 × 9 ÷ 4 = 7.07 m².
Find the radius first: r = C ÷ 2π. A tape round a tree of 10 m gives r = 1.59 m and an area of 7.96 m².
C = 2 × π × r, or π × d. A 3 m diameter circle has a circumference of 9.42 m, the length of edge formwork around it.
A circle 10 ft across has r = 5 ft, so 3.1416 × 25 = 78.5 ft².