CIRCLE CALCULATOR
Radius or diameter in • circumference, area and missing measure out
Useful for circle formulas, GCSE maths revision and quick checks
GIVEN
R
The calculator finds the other value too
ROUNDING
2DP
Result rounding only
RADIUS
X
Enter radius
π
CONST
π is built in
WORKING
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—
—
—
—
CIRC / AREA
READY
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PAGE SUMMARY
Use this page to calculate circle radius, diameter, circumference and area.
You can start from radius or diameter and the missing circle values are worked out automatically.
Useful for circle formula practice, homework checks and GCSE maths revision.
Circumference uses ordinary units. Area uses square units such as cm².
More formulas, worked examples and extra circle help are on the next pages.
Related Teletext-Tools pages are linked below for area, perimeter, surface area and the main maths index.
HOW TO USE
Choose whether you are given radius or diameter.
Enter the value, press SOLVE and read the missing circle measures.
The working shows the conversion step before the main formulas.
CIRCLE FORMULAS
d = 2r
r = d ÷ 2
C = 2πr = πd
A = πr²
UNITS
Circumference is a length, so it uses ordinary units.
Area is measured in square units such as cm² or m².
WORKED EXAMPLE
Given r = 4
d = 2 × 4 = 8
C = 2π × 4 ≈ 25.13
A = π × 4² ≈ 50.27
ROUNDING TIP
Keep the full calculator value during the method and round at the end.
That gives a more accurate final answer in exams and homework.
WHY THIS PAGE HELPS
It combines circle formulas, substitution and answers in one place.
That makes it useful for quick checking and revision as well as live calculations.
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CIRCLE CALCULATOR HELP
This page is useful when you need the circumference and area of a circle quickly.
It also helps when you know only the radius or only the diameter.
The calculator turns one measurement into the other before applying the formulas.
GCSE CIRCLE TOPIC
Circle formulas are a standard GCSE maths topic.
They often appear in perimeter, area, sectors and problem-solving questions.
COMMON SEARCHES
circle calculator radius diameter circumference area
circumference and area calculator
circle formula calculator with working
GCSE circle area circumference help
WHY THE WORKING MATTERS
Seeing the conversion from radius to diameter or back again helps avoid simple mistakes.
It also shows why circumference and area use different formulas.
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MORE EXAMPLES
If d = 10, then r = 5
C = π × 10 ≈ 31.42
A = π × 5² ≈ 78.54
QUICK CHECKS
Diameter is always twice the radius.
Circumference grows in a straight way with the radius.
Area grows faster because the radius is squared.
RELATED TELETEXT-TOOLS PAGES
LOOP BACK
Use NEXT to return to Page 1 and keep calculating.
This keeps the calculator clear while still giving stronger extra help pages.
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GIVEN
R
The calculator finds the other value too
ROUNDING
2DP
Result rounding only
RADIUS
X
Enter radius
π
CONST
π is built in
WORKING
—
—
—
—
—
CIRC / AREA
READY
—
PAGE 1/4
HOW TO USE
Choose whether the given measure is radius or diameter.
Enter the value and press SOLVE.
The page works out the missing measure, circumference and area.
FORMULAS
d = 2r
r = d ÷ 2
C = 2πr = πd
A = πr²
WORKED EXAMPLE
r = 4 → d = 8
C ≈ 25.13
A ≈ 50.27
UNITS
Circumference uses ordinary units.
Area uses square units such as cm².
Round at the end for better accuracy.
PAGE 2/4
CIRCLE HELP
This page helps when you need circumference and area from one circle measurement.
It works from radius or diameter and shows the key circle formulas clearly.
GCSE REVISION
Circle formulas often appear in GCSE perimeter and area questions.
They also connect with sectors, arcs and compound shapes.
COMMON SEARCHES
circle calculator radius diameter circumference area
circumference and area calculator
circle formula calculator with working
WHY THE METHOD HELPS
The conversion step helps avoid mixing up radius and diameter.
That is one of the most common circle mistakes.
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