How to calculate the area of ​​a semicircle: 3 steps (with pictures)

A semicircle is half of a… circle! To calculate the area of ​​such a figure, you must first calculate the area of ​​the circle and divide by two. In this article we explain how to calculate the area of ​​a semicircle.

Steps

Step 1. Find the radius of the semicircle

Indeed, you need to know the radius of the semi-circle. Take the case of a semicircle 5 cm in radius.

If we only give you the diameter, nothing could be simpler: you divide it by 2 to get the radius. For example, if your figure has a diameter of 10 cm, the radius will be 5 cm

Step 2. Next, calculate the area of ​​the entire circle, then divide by two

The formula for calculating the area of ​​a circle is: πr2, where "r" is the radius of the circle. Since your goal is to find "half" of the area of ​​the circle, you first apply the formula for the circle, then you divide by 2. If we were to write the formula for the area of ​​a semicircle, it would be this one: πr2/2. Let's move on to the digital application with our “5 cm” radius. As for the constant π, either you use the "pi" key of your calculator (the calculation will be more precise), or you take an approximate value, that is to say 3, 14. In the formula, you can leave π in its literal form. The following calculations are obtained.

• 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

Step 3. Remember to express your results in a square unit

Here it will be cm2. You are working with two dimensions. With three dimensions (we add a height or a depth), we obtain volumes and the units are therefore cubic, like the cm3.