Maths - Semi-Circles


This page allows you to calculate every dimension of a Semi-Circle. The actual shape that you are interested in can be any object whatsoever, possibly a flower bed in a garden, a patio, or any other DIY task.
Click on any of the links at the top of the page to reveal (or hide) more information about this calculator.


If you are reading this paragraph, then you probably don't have JavaScript installed/enabled on your computer.
At this point in time the calculators on this site are entirely dependent on JavaScript. Given enough time and money it is hoped to develop a version in the future which will be able to operate independently. Since JavaScript runs on your own computer, rather than on this server, it has been possible to set up this site much more quickly than if a server-side language was used, and it is possible to serve far more pages with the available bandwidth.


Radius r
The distance from the centre of a semi-circle to any point on the circumferance of the curved part.
Diameter d
The furthest distance between opposite sides of the semi-circle, equal to twice the radius.
Perimeter / Circumferance c
The distance measured once around the edge of the semi-circle, including the straight bit.
Area a
The area bounded by the circle.
An important constant, with an approximate value of 3.14, and an exact value very close to 22/7
On this computer the value used is:



  1. Fill in as many boxes as you can with the values that you know
  2. Choose the correct units for all 'input' fields, or leave as 'Units' if not required
  3. Choose the correct units for any output fields that you require
  4. Click the 'Calculate' button below the input fields
  5. The value of the blank fields will be calculated
  6. A 'Results Area' will be displayed below.
  7. All known values will be shown. (Values for which insufficient information was given will also be identified.)
  8. To do further calculations simply change any values in the input fields and click the 'Calculate' button again. (Press the 'Clear Form' button if you want to empty all of the input fields.)
  9. Press the 'Clear Results' button if you wish to discard the first results, otherwise further calculations will be added into the same area.
  10. Click the 'Calculate' button again
  11. Click the 'Print Results' button to display all current results in a new, printable window.
Diagram showing dimensions


© Copyright Mike Brockington 2004 - 2021   All Rights Reserved