Circle Calculator
Know one measurement of a circle and need the rest? Enter the radius, diameter, circumference or area and this calculator works out all four values for you.
How to use the circle calculator
- Choose which property you already know: radius, diameter, circumference or area.
- Type its value into the input field.
- Read the radius, diameter, circumference and area, which update as you type.
Examples
From a radius
radius = 5
diameter 10, circumference 31.4159, area 78.5398
From an area
area = 78.5398
radius 5, diameter 10, circumference 31.4159
Frequently asked questions
What are the formulas for a circle?
With radius r: diameter = 2r, circumference = 2 x pi x r, and area = pi x r squared. The constant pi is about 3.14159.
What is the difference between area and circumference?
Circumference is the distance around the circle (a length), while area is the space inside it (a square measure). They use different formulas, so they are not interchangeable.
What is the difference between radius and diameter?
The radius runs from the center to the edge. The diameter runs all the way across through the center, so the diameter is always twice the radius.
How do I find the radius from the area?
Divide the area by pi, then take the square root. For example, an area of about 78.54 gives a radius of 5 because the square root of 78.54 divided by pi is 5.
What is pi and which value does this tool use?
Pi is the ratio of a circle's circumference to its diameter, an irrational number near 3.14159. The calculator uses the full precision value built into your browser.
Where is a circle calculator useful in real life?
It helps with sizing pizzas, pipes and round tables, planning circular gardens or pools, estimating material for a round rug, and checking geometry homework.
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