What is the area of a circle with radius 18 mm?

Here is the answer to questions like: how to find the area of a circle with radius 18 mm?

Circle Calculator

Inputs:

Radius:		or
Diameter		or
Circumference:
Unit:

The area of a circle with radius 18 is 1018
Formulae:
	A = πr² = π(d2)² A = C²4π π = 3.1415 A = area C = circumference or perimeter r = radius, d = diameter

Solution Steps:

Area of a circle in terms of radius:

Area = π·r² = 3.14·18² = 1018 square mm^(*)

Area of a circle in terms of diameter:

Area = π·(d2)² = 3.14·(362)² = 3.14·(18)² = 1018 square mm^(*)

Area of a circle in terms of circumference:

Area = C²4π = 113.1²4π = 12791.61(4·3.14) = 12791.6112.56 = 1018 square mm^(*)

^(*) 1017.8760197631 mm, exactly or limited to the precision of this calculator (13 decimal places).

Note: for simplicity, the operations above were rounded to 2 decimal places and π was rounded to 3.14.

Result in other units of area:

A circle of radius = 18 or diameter = 36 or circumference = 113.1 mm has an area of:

1.018 × 10^-9 square kilometers (km²)
0.001018 square meters (m²)
10.18 square centimeters (cm²)
1018 square millimeters (mm²)
3.93052 × 10^-10 square miles (mi²)
0.00121752 square yards (yd²)
0.0109577 square feet (ft²)
1.5779 square inches (in²)

Use the this circle area calculator below to find the area of a circle given its radius, or other parameters. To calculate the area, you just need to enter a positive numeric value in one of the 3 fields of the calculator. You can also see at the bottom of the calculator, the step-by-step solution.

Formula for area of a circle

Here a three ways to find the area of a circle (formulas):

Circle area formula in terms of radius

A = πr²

Circle area formula in terms of diameter

A = π(d2)²

Circle area formula in terms of circumference

A = C²4π

See below some definitions related to the formulas:

Circumference

Circumference is the linear distance around the circle edge.

Radius

The radius of a circle is any of the line segments from its center to its perimeter. The radius is half the diameter or r = d2.

Diameter

The diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. The diameter is twice the radius or d = 2·r.

The Greek letter π

π represents the number Pi which is defined as the ratio of the circumference of a circle to its diameter or π = Cd . For simplicity, you can use Pi = 3.14 or Pi = 3.1415. Pi is an irrational number. The first 100 digits of Pi are: 3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 ...

Note:

If you input the radius in centimeters, you will get the answer in square centimeters (cm²), if in inches, will get the answer in square inches (in²) and so on ...

Circumference is often misspelled as circunference.

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