No personal result is available. These are the circle formulas and conditions.
Formulas and conditions
Circle
Radius / diameter
Circumference
Area
r radius · d diameter · O center · A area · C circumference
r > 0. π is exact; use ≈ for rounded answers.
Using d as r makes the area four times too large.
Diagrams are schematic, not to scale.
Radius runs from the center to the edge. Diameter crosses the center from edge to edge, so divide a known diameter by two before using a radius formula.
π remains exact in a multiple such as 25π. A decimal with ≈ is rounded; the calculator uses π without rounding it to 3.14 first.
Use the same length unit throughout a formula. Convert mixed measurements first. Length and perimeter use units such as cm; area uses cm²; volume uses cm³. Decimal examples below are rounded to at most six significant figures, with ≈ marking an approximation.
Worked example: A circle with diameter 10 cm
r = 10 ÷ 2 = 5 cm.
A = π × 5² = 25π cm² ≈ 78.5398 cm².
C = π × 10 = 10π cm ≈ 31.4159 cm.
The two circumference expressions agree: 2π × 5 = π × 10. Using diameter 10 as radius would make the area four times too large.