How to calculate circle area
Area = π × radius². Use consistent length units; the result is in square units. For example, measurements in metres produce square metres (m²). Enter the measured dimensions, select the matching method and choose Calculate area.
Practical questions
How do I calculate the area of a round table?
Measure its diameter through the centre. For a diameter of 2 m, select Diameter and enter 2. The area is approximately 3.141592654 m². A tablecloth with overhang needs a larger diameter.
Can I find area from a measurement around the edge?
Yes. Select Circumference. The calculator finds radius = circumference ÷ (2π), then calculates area. Keep the measuring tape on the circular boundary.
What is the difference between radius and diameter?
Radius runs from the centre to the edge. Diameter runs from one edge through the centre to the opposite edge and is twice the radius. Entering diameter as radius makes the calculated area four times too large.
Does doubling the diameter double the area?
No. Doubling diameter doubles radius, so area becomes four times as large. Circumference, however, only doubles.
Can I calculate the area of a circular ring?
Calculate the outer circle’s area and subtract the inner circle’s area. Use matching units and do not subtract the radii first: ring area is π times the difference of the squared radii.
How much larger is a 40 cm pizza than a 30 cm pizza?
Using diameter mode, the areas are about 1,256.64 cm² and 706.86 cm². The area ratio is 40² ÷ 30² = 16/9, so the 40 cm pizza has about 77.8% more area. Comparing value also requires prices and assumes thickness and toppings are comparable.
Can I estimate the surface area of a round pond?
For a circular pond with a 4 m diameter, the surface area is about 12.57 m². That is the flat surface area only. It does not give water volume or the liner area, which also depend on depth, side slopes and any overlap needed at the edge.
How do I find the area of a path around a circular bed?
Subtract the inner circle’s area from the outer circle’s area. For a bed with radius 2 m and a path 1 m wide, the outer radius is 3 m. The path area is π × (3² − 2²) = 5π, or about 15.71 m². The path width is added to the radius, not used as the outer radius.
How much edging is needed around a circular flower bed?
Use the circumference result. A bed with a 3 m diameter has a circumference of 3π, or about 9.42 m. Its area is about 7.07 m². Edging is bought by length, while soil coverage or turf is usually measured by area; any gaps or joining allowance need separate consideration.
Can I estimate the area of a semicircular window?
Calculate the area of the full circle using the window’s full width as the diameter, then divide by two. A semicircle with diameter 2 m has an area of π/2, or about 1.57 m². Its complete boundary includes both the curved edge and the straight diameter.
What if a round object is actually oval?
A circle assumes the same diameter in every direction through its centre. If the longest and shortest diameters differ, an ellipse model may be more suitable. Do not simply average those diameters and assume the circle result is exact. For irregular outlines, a more detailed measurement method is needed.