What is the area of a circle with radius 11?

The area is 121π, which is 380.132711 square units. The formula is A = πr², so squaring the radius gives 11 × 11 = 121, and multiplying by π gives 380.132711. Because the radius squares, the area of this circle is 121 times that of the unit circle rather than 11 times.

What is the circumference of a circle with radius 11?

The circumference is 22π, or 69.115038 units. It comes from C = 2πr, so 2 × 11 = 22, then × π. The same circle has a diameter of 22, and since C = πd you can get there either way — 22π is the same as 22π. Dividing the circumference by the diameter returns π itself, 3.14159265, which is true for every circle and is where the constant comes from.

How much bigger is radius 11 than radius 10?

The radius goes up by 10%, from 10 to 11, but the area goes up by 21% — from 314.159265 to 380.132711. That is the square law: the area ratio is (11/10)² = 1.21. The circumference, being linear, rises by the same 10% as the radius.

What fits inside a circle of radius 11?

A square inscribed in it has a diagonal equal to the diameter, 22, so its side is 11√2 = 15.556349 and its area is 2r² = 242 — about 63.7% of the circle, a proportion that is the same for every circle. A regular hexagon inscribed in it has a side of exactly 11, since the hexagon side always equals the radius, giving a perimeter of 66 against a circumference of 69.115038.

How was π first calculated?

By squeezing. Archimedes inscribed and circumscribed regular polygons around a circle and computed both perimeters, knowing the true circumference lay between them. With 96-sided polygons he pinned π between 223/71 and 22/7 — that is, between 3.1408 and 3.1429. The method is exact in principle and only limited by how many sides you have the patience for.

Can a circle’s area ever be a whole number?

Only if the radius is irrational in the right way. Since A = πr², getting a whole number area requires r² to be a whole number divided by π, and π is transcendental, so no rational radius will ever do it. A radius of 1 gives an area of π, a radius of 10 gives 100π — always a multiple of π, never a plain integer. Working the other way round, entering an area of 100 gives a radius of 5.641896.

What is the difference between a chord, an arc and a segment?

A chord is a straight line joining two points on the circle; the diameter is the longest one there is. An arc is the curved part of the circumference between those same two points. A segment is the region between a chord and its arc, whereas a sector is the region between two radii and their arc. The distinction matters because the formulas are quite different.

Why is 360 degrees a full turn?

Convention inherited from Babylonian astronomy, which counted in sixties and used a 360-day year. It survives because 360 divides evenly by so much — 2, 3, 4, 5, 6, 8, 9, 10, 12 and more — which makes common fractions of a circle come out as whole numbers of degrees. Mathematics itself prefers radians, where a full turn is 2π, because that is the unit in which the calculus of circles behaves.

What are the formulas for a circle?

Three, and they all hang off the radius. The diameter is d = 2r. The circumference is C = 2πr, which is the same as πd. The area is A = πr². If you have any one of the four quantities you can recover the other three, which is what the mode buttons on this calculator do — enter a circumference or an area and it works backwards to the radius first.

Circle with Radius 11

A circle of radius 11 has an area of 380.132711 and a circumference of 69.115038, with a diameter of 22. Both of those are exact multiples of π before they are turned into decimals — the area is 121π and the circumference is 22π — which is worth seeing, because it is where the irrationality lives. N...

CIRCLE CALCULATOR

SOLVE FROM

Radius (r)

Must be greater than 0

Central Angle θ (optional) — for arc length & sector area

RADIUS (r)

units

DIAMETER (d)

units

CIRCUMFERENCE (C)

69.115038

units

AREA (A)

380.132711

units²

STEP-BY-STEP

Given: radius r = 11

Diameter: d = 2r = 2 × 11 = 22

Circumference: C = 2πr = 2 × π × 11 = 69.115038

Area: A = πr² = π × 11² = 380.132711

QUICK EXAMPLES

LIVE DIAGRAM

EXACT EXPRESSIONS

Circumference11π × 2 = 69.115038

Areaπ × 11² = 380.132711

C/d ratioπ = 3.14159265...

Created with❤️byeaglecalculator.com

HOW TO USE

1
The answer is already here: a circle of radius 11 has an area of 380.132711 and a circumference of 69.115038. This page opens with the radius set to 11, so nothing needs typing.
2
Read the four result tiles — radius 11, diameter 22, circumference 69.115038 and area 380.132711. The STEPS panel underneath shows each one being derived rather than just asserted.
3
Add an angle to get a wedge. A 90° sector of this circle has an arc of 17.27876 and an area of 95.033178; a 60° sector has an arc of 11.519173 and an area of 63.355452.
4
Switch the input mode to run the same circle backwards — enter the area 380.132711 or the circumference 69.115038 and it recovers the radius 11, which is a useful check that everything is consistent.

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Last updated: July 28, 2026 · Formula verified by EagleCalculator team · Eagle-eyed accuracy for every calculation.