Area of a circle calculator  calculating area of a circle online. Area of a circle  is a numerical characteristic that characterizes the size of a plane bounded by a circle line. Area of a circle can be calculated using the number pi and the radius of the circle, or using other known input data. Our calculator will help you to calculate the area of a circle for free online or to check the already performed calculations.
Table with circle area formulas (at the end of the page)
1
Circle Area Through Radius
2
Circle area through diameter
3
Area of a circle along the circumference
4
Area of a circle through a square inscribed in a circle
5
Area of the circle inscribed in a square
6
Area of the circle described around an arbitrary triangle
This formula is applicable only if a circle can be described around a triangle, that is, all three vertices of the triangle must lie on the line of the circle. The triangle in this case can be any.
To calculate the area of a circle, first calculate the semiperimeter of a triangle
7
Area of a circle described near an equilateral triangle
8
Area of a circle described around an equilateral triangle, calculated from the height of the triangle
9
Area of a circle about an isosceles triangle
10
Area of the circle described about a right triangle
11
Area of a circle inscribed in an isosceles triangle
12
Area of a circle inscribed in an isosceles triangle, calculated on the sides of the triangle and the angle between them
13
Area of a circle inscribed in a right triangle
14
Area of a circle inscribed in a right triangle, calculated by the side and angle
15
Area of a circle inscribed in an equilateral triangle
16
Area of a circle inscribed in an isosceles trapezium, calculated from the base of the trapezium and the angle at the base
17
Area of a circle described near an isosceles trapezium, calculated along the sides of the trapezium, its diagonal and base
To calculate the area of a circle, first calculate the semiperimeter of a triangle ABC
18
Area of the circle described near the rectangle
19
Area of a circle described near a regular polygon
20
Area of a circle described about a regular hexagon
Note:
If the angle is specified in radians in the source data, then for conversion to degrees you can use the formula:
Table with circle area formulas
initial data (active link to go to the calculator) 
sketch  formula  
1  radius  
2  diameter  
3  circumference  
4  side of a square  
5  side of a square  
6  side of the triangle 
where


7  side of an equilateral triangle  
8  equilateral triangle height  
9  side and base  
10  side at right angle of triangle  
11  side and base  
12  sides and angle between them  
13  side of a right triangle  
14  side and angle at the base of the triangle  
15  side of an equilateral triangle  
16  side and angle at the base of the trapezoid  
17  sides and diagonal of the trapezoid 
where


18  side of the rectangle  
19  side and number of sides of the polygon  
20  hexagon side 