Last updated: April 2026
Type into one field and the others are solved from that measurement.
Arc length
7.854 cm
Sector area
19.635 cm²
Chord length
7.0711 cm
Segment area
7.135 cm²
pi used: 3.14159265358979... Results are rounded to 4 decimal places.
A circle can be solved from one measurement because radius, diameter, circumference, and area are all linked by pi.
Pi is the constant ratio between a circle's circumference and its diameter. It begins 3.14159 and continues forever without repeating.
A central angle selects part of a circle. The same fraction of 360 degrees applies to circumference for arc length and to total circle area for sector area.
The Circle Calculator solves common circle measurements including radius, diameter, circumference, and area. It is useful for maths homework, geometry revision, DIY planning, machining, craft projects, garden layouts, round tables, circular patios, and any situation where one circle measurement needs to be converted into the others.
Circle calculations are based on pi. Diameter is twice the radius, circumference is pi times diameter, and area is pi times radius squared. If the input is circumference or area, the calculator rearranges those formulas to solve for radius first.
Input: Radius 5 cm
Calculation: pi x 5^2
Result: Area is about 78.54 cm2 and circumference is about 31.42 cm.
Input: Diameter 1.2 m
Calculation: pi x 1.2
Result: Circumference is about 3.77 m.
Most circle problems start with one known measurement. If you measure across the circle through the centre, you have diameter. If you measure from the centre to the edge, you have radius. If you measure around the outside edge, you have circumference.
| Need | Use | Note |
|---|---|---|
| Diameter | 2 x radius | Diameter crosses the centre |
| Circumference | pi x diameter | Distance around the outside |
| Area | pi x radius squared | Surface inside the circle |
| Radius from area | sqrt(area / pi) | Useful when area is known first |
Circle calculations are often used before area, volume, and material estimates. For example, a circular patio needs circle area, a cylinder tank needs circular base area, and a round border may need circumference for edging material.
This calculator follows standard geometry formulas. It does not account for measurement error, material waste, installation tolerances, or real-world irregular shapes.
Use area = pi x radius squared.
Use circumference = pi x diameter, or 2 x pi x radius.
Yes. Diameter equals 2 times radius.
Yes. Radius equals the square root of area divided by pi.
The calculator uses a precise pi value internally and rounds the displayed result.
This calculator is designed to help you understand the likely number before you make a decision or start an application.
Your result should be checked against official UK guidance, especially if your circumstances include dependants, exemptions, prior leave, or a complex immigration history.
Treat the figure as a planning tool rather than legal advice. Where the answer affects an application deadline or major payment, speak to an authorised adviser.
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