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.

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## Circle Area Through Radius

**r**- radius

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## Circle area through diameter

**D**- diameter

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## Area of a circle along the circumference

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## Area of a circle through a square inscribed in a circle

**a**- side

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## Area of the circle inscribed in a square

**A**- side

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## 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 semi-perimeter of a triangle

**a**- side

**b**- side

**c**- side

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## Area of a circle described near an equilateral triangle

**a**- side

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## Area of a circle described around an equilateral triangle, calculated from the height of the triangle

**h**- height

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## Area of a circle about an isosceles triangle

**a**- side

**b**- base

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## Area of the circle described about a right triangle

**a**- side

**b**- side

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## Area of a circle inscribed in an isosceles triangle

**a**- side

**b**- base

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## Area of a circle inscribed in an isosceles triangle, calculated on the sides of the triangle and the angle between them

**b**- side

**α**- angle between parties

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## Area of a circle inscribed in a right triangle

**a**- side

**b**- side

**c**- side

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## Area of a circle inscribed in a right triangle, calculated by the side and angle

**b**- side

**α**- angle at base

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## Area of a circle inscribed in an equilateral triangle

**a**- side

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## Area of a circle inscribed in an isosceles trapezium, calculated from the base of the trapezium and the angle at the base

**b**- side

**α**- angle at base

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## 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 semi-perimeter of a triangle *ABC*

**a**- side

**c**- side

**d**- diagonal

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## Area of the circle described near the rectangle

**a**- side

**b**- side

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## Area of a circle described near a regular polygon

**a**- side

**N**- the number of sides of the polygon

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## Area of a circle described about a regular hexagon

**a**- side