How to Find the Area of a Semicircle: Formula & Calculation Tips

Reviewed by Grace Imson, MA

Last Updated: April 9, 2025 Fact Checked

A semi-circle is half of a circle. Therefore, to find the area of a semi-circle, you just have to find the area of a full circle and then divide it by two. It will be faster than you think.^{[1]
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1
Find the radius of the semi-circle. You'll need the radius to find the area of the semi-circle. Let's say the radius of the semi-circle is 5 centimeter (2.0 in).
- If you're only given the diameter of the circle, you can divide it by two to get the radius. For example, if the diameter of the circle is 10 centimeter (3.9 in), then you can divide it by 2 (10/2) to get 5 centimeter (2.0 in) as the radius.^{[2]
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2
Find the area of the full circle and divide it by two. The formula for finding the area of a full circle is πr², where "r" represents the radius of the circle. Since you're finding the area of a semi-circle, you'll be looking for half of the area of a circle,^{[3]
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Research source} which means you have to use the formula for finding the area of a semi-circle and then divide it by two. So, the formula you'll have to use to find the area of a semi-circle is πr²/2. Now, just plug "5 centimeter (2.0 in)" into the formula to get your answer. You can either use the closest approximation for π with your calculator, substitute 3.14 for π, or you can just leave the symbol in place. Here's how you do it:
- Area = (πr²)/2
- Area = (π x 5 cm x 5 cm)/2
- Area = (π x 25 cm²)/2
- Area = (3.14 x 25 cm²)/2
- Area = 39.25 cm²
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Since you're finding the area of a shape, you'll have to use units square d (such as cm²) in your answer to indicate that you're working with a two-dimensional object.^{[4]
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Research source} If you're calculating volume, then you'll be working with cubic units (such as cm³).

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How do I find the area of a circle?

Donagan

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Multiply pi by the square of the radius.

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Should I follow PEMDAS in the formula?

Donagan

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Yes, PEMDAS has to be used because of the exponentiation, you have to do that first. If you rewrite it as π×r×r/2 then you don't have to worry about PEMDAS, because it involves only multiplication and division.

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What is the area of a semicircle with the radius of 1.4 m?

Community Answer

Given a radius of circle = 1.4m. As we know, the area of semicircle=((pie)*r*r)/2=(3.14*1.4*1.4)/(2)=3.078 m square.

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The area of a semicircle is (1/2)(pi)(r^2).^{[5]
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The area of a circle is (pi)(r^2).^{[6]
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Warnings

Be careful not to use the diameter in the formula for finding area! If the diameter is given, then remember to divide it by 2 to get the radius.

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