How to Find the Area of a Semicircle

Download Article
Download Article

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]

Steps

Download Article
  1. {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/8\/89\/Find-the-Area-of-a-Semicircle-Step-1-Version-3.jpg\/v4-460px-Find-the-Area-of-a-Semicircle-Step-1-Version-3.jpg","bigUrl":"\/images\/thumb\/8\/89\/Find-the-Area-of-a-Semicircle-Step-1-Version-3.jpg\/aid1698440-v4-728px-Find-the-Area-of-a-Semicircle-Step-1-Version-3.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"<div class=\"mw-parser-output\"><p>\u00a9 2024 wikiHow, Inc. All rights reserved. wikiHow, Inc. is the copyright holder of this image under U.S. and international copyright laws. This image is <b>not<\/b> licensed under the Creative Commons license applied to text content and some other images posted to the wikiHow website. This image may not be used by other entities without the express written consent of wikiHow, Inc.<br>\n<\/p><p><br \/>\n<\/p><\/div>"}
    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]
  2. {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/d\/da\/Find-the-Area-of-a-Semicircle-Step-2-Version-3.jpg\/v4-460px-Find-the-Area-of-a-Semicircle-Step-2-Version-3.jpg","bigUrl":"\/images\/thumb\/d\/da\/Find-the-Area-of-a-Semicircle-Step-2-Version-3.jpg\/aid1698440-v4-728px-Find-the-Area-of-a-Semicircle-Step-2-Version-3.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"<div class=\"mw-parser-output\"><p>\u00a9 2024 wikiHow, Inc. All rights reserved. wikiHow, Inc. is the copyright holder of this image under U.S. and international copyright laws. This image is <b>not<\/b> licensed under the Creative Commons license applied to text content and some other images posted to the wikiHow website. This image may not be used by other entities without the express written consent of wikiHow, Inc.<br>\n<\/p><p><br \/>\n<\/p><\/div>"}
    The formula for finding the area of a full circle is πr 2 , 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] 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 πr 2 /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 = (πr 2 )/2
    • Area = (π x 5 cm x 5 cm)/2
    • Area = (π x 25 cm 2 )/2
    • Area = (3.14 x 25 cm 2 )/2
    • Area = 39.25 cm 2
    Advertisement
  3. {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/d\/d4\/Find-the-Area-of-a-Semicircle-Step-3-Version-2.jpg\/v4-460px-Find-the-Area-of-a-Semicircle-Step-3-Version-2.jpg","bigUrl":"\/images\/thumb\/d\/d4\/Find-the-Area-of-a-Semicircle-Step-3-Version-2.jpg\/aid1698440-v4-728px-Find-the-Area-of-a-Semicircle-Step-3-Version-2.jpg","smallWidth":460,"smallHeight":345,"bigWidth":728,"bigHeight":546,"licensing":"<div class=\"mw-parser-output\"><p>\u00a9 2024 wikiHow, Inc. All rights reserved. wikiHow, Inc. is the copyright holder of this image under U.S. and international copyright laws. This image is <b>not<\/b> licensed under the Creative Commons license applied to text content and some other images posted to the wikiHow website. This image may not be used by other entities without the express written consent of wikiHow, Inc.<br>\n<\/p><p><br \/>\n<\/p><\/div>"}
    Since you're finding the area of a shape, you'll have to use units square d (such as cm 2 ) in your answer to indicate that you're working with a two-dimensional object. [4] If you're calculating volume, then you'll be working with cubic units (such as cm 3 ).
    4. Advertisement

Video

Community Q&A

Search
Add New Question
  • Question
    How do I find the area of a circle?
    Donagan
    Top Answerer
    Multiply pi by the square of the radius.
    Thanks! We're glad this was helpful.
    Thank you for your feedback.
    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
    Yes No
    Not Helpful 61 Helpful 75
  • Question
    Should I follow PEMDAS in the formula?
    Donagan
    Top Answerer
    You don't have to worry about PEMDAS, because the formula involves only multiplication and division.
    Thanks! We're glad this was helpful.
    Thank you for your feedback.
    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
    Yes No
    Not Helpful 47 Helpful 49
  • Question
    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.
    Thanks! We're glad this was helpful.
    Thank you for your feedback.
    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
    Yes No
    Not Helpful 105 Helpful 84
See more answers
Ask a Question
200 characters left
Include your email address to get a message when this question is answered.
Submit
      Advertisement

      Tips

      Submit a Tip
      All tip submissions are carefully reviewed before being published
      Submit
      Thanks for submitting a tip for review!
      Advertisement

      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.
        Thanks
      Advertisement

      You Might Also Like

      How to
      Calculate the Area of a Circle
      How to
      Calculate the Circumference of a Circle
      How to
      Calculate the Area of a Sector
      How to
      Calculate Square Meters
      How to
      Calculate the Area of a Trapezoid
      How to
      Find the Surface Area of a Rectangular Prism
      How to
      Calculate the Area of a Triangle
      How to
      Find the Area of a Regular Pentagon
      How to
      Calculate the Area of a Polygon
      How to
      Find Surface Area
      How to
      Calculate the Area of a Rhombus
      How to
      Find the Area of Regular Polygons
      How to
      Find the Area of a Shape
      How to
      Find the Area of a Circle Using Its Circumference
      Advertisement

      References

      1. ↑ https://www.mathopenref.com/semicircle.html
      2. ↑ https://www.khanacademy.org/math/cc-seventh-grade-math/cc-7th-geometry/cc-7th-area-circumference/e/area-and-circumference-of-parts-of-circles
      3. ↑ https://www.mathsisfun.com/geometry/circle-area-by-sectors.html
      4. ↑ https://www.khanacademy.org/math/cc-seventh-grade-math/cc-7th-geometry/cc-7th-area-circumference/e/area-and-circumference-of-parts-of-circles
      5. https://www.mathopenref.com/semicircle.html

      About This Article

      Article Summary X

      To find the area of a semicircle, start by finding the area of the full circle using the formula πr^2, where r is the radius of the circle. If you don't know the radius, you can find it by dividing the diameter of the circle by 2. Once you've found the area of the full circle, just divide it by 2 to find the area of the semicircle. If you want to learn how to label your answer with the correct units, keep reading the article!

      Did this summary help you?
      In other languages
      Thanks to all authors for creating a page that has been read 779,449 times.

      Reader Success Stories

      • Zuri Wanjiru

        Jul 21, 2018

        "i was revising for my exams and I forgot how to find the area of a semi circle and I knew wikiHow would help me!"
        Rated this article:
      More reader stories Hide reader stories
      Share your story

      Did this article help you?

      Advertisement