Illustrator doesn’t have a half-circle tool but it does have an ellipse tool which you can use to make perfect circles. And once you have a perfect circle Illustrator offers a lot of ways to cut that circle in half.  Voila! semi-circle.

Tip: For any of the methods below start by creating a perfect circle by choosing the ellipse tool and then click and shift-drag to make a perfect circle. Holding the shift key down constrains the tool so the width and height are equal. I like to select the circle with my selection tool so that I can see the anchor points. This makes it easier to position my other tools for the techniques below.

Create a Half Circle in Illustrator

Method 1: Use the Knife Tool.

Select your knife tool and position it directly over the anchor point on the left side of the circle and hold down the Alt + Shift (Windows) or  Opt + Shift (Mac) keys and drag the knife all the way across to or past the anchor point on the right side of the circle. 

Note: Holding the Alt / Opt key down forces the tool to draw a straight line adding the shift key forces that line to be horizontal, vertical or at a 45 degree angle (in this case because we are dragging sideways it will constrain the tool to the horizontal).

object selected with direct selection vs selection tool in illustrator

Note: Objects selected with a direct selection tool(white arrow) show anchor points and objects selected with the selection tool (black arrow) show a bounding box.

Dude Where’s my Knife:  If you can’t find your knife tool: it’s normally grouped with the scissor and eraser tools but the basic version of the toolbox is smaller and just has the “essentials”.  Look at the bottom of the toolbox and choose the Edit Toolbar icon  (3 dots ) and you will see a flyout with ALL the tools available. This palette is so big it has its own scroll bar and you may need to scroll down a bit to get to the knife. Once you find the knife tool clicking will select it for use.

toolbox optionsYou can also change the toolbox from Basic to Advanced (which has the 2 column layout with more tools) by choosing the Edit Toolbox button (3 dots) and then at the top of that window choose the toolbox options button  (looks like a list icon) and you can switch between the two layouts from the resulting flyout menu.

edit the toolbox

Method 2: Use  Divide Objects Below

  1. Choose the line segment tool and then hold the shift key down while you drag out a horizontal line. Note: Using the shift key modifier will constrain the line to be perfectly horizontal. Drag a marquee selection so it touches both circle and line and use the align options on the properties panel to vertically center both objects. The result will be that the line is now over the exact center of the circle.
use the vertical align option from the properties palette to align the line to the absolute vertical center of the circle
  1. Select the line (just the line!) and from the menu at the top choose Object > Path > Divide Objects Below

Method 3: Use the Scissor Tool

  1. Select your circle shape using the direct selection tool (white arrow). This will allow you to see the anchor points on the side of the circle.
  2. Select your scissor tool and position and click directly on the anchor point on the left side of the circle. The anchor point will enlarge when you are directly over it. Then repeat for the anchor point on the other side.
    move scissor tool over anchor point and clickonly the outside of the object has a stroke
  3. Now this looks like a perfect semi-circle but this produces an unclosed shape. If you look closely you will see that the line that goes around the shape ends at the anchor points we cut at. Sometimes this is useful for what you are doing but… to finish this off we want to produce a closed shape and we can do that by selecting the pathfinder palette and clicking the UNITE icon.
    use the pathfinder panel to unit the shape to close it
    half-circle is now a closed shape

Method 4:  Delete an Anchor Point and Join

This is my preferred method as I commonly already have the direct selection tool selected when working and then it is just one hot-key combination to finish.

  1. Use your direct selection tool (white arrow) to select one of the anchor points. You can tell only 1 of the anchor points is selected because it will be filled while the other anchor points will show as empty (the other lines with the little circles on the ends are direction handles and they allow you to adjust curves).
    select anchor point
  2. Hit delete on your keyboard.
  3. This creates a half-circle but it is an unclosed shape we need one more step to finish this. We need to close the path, essentially drawing a line across from the end anchor point on one side of the semi-circle to the anchor point at the other side.  We did this with the pathfinder panel in the method above but this time we are going todo this by joining.  First, we need to select both end anchor points by drawing a marquee (box) around them with the direct selection tool. You can tell they are selected because they will be solid/filled and unselected anchor points will appear hollow.  Then we can either choose the join option from the properties panel or use a hot key combination CTRL + J (Windows) or CMD +  J (Mac).
    close half-circle-shape by joining

Method 5: Use DIVIDE from the Pathfinder Palette.

  1. Draw out a perfect circle by using the Ellipse tool and holding the Shift Key down as you drag so the shape is constrained to the same height and width.
  2. Select the rectangle tool and position your cursor close to the left anchor point on the circle – watch for the smart guides to signal that you are aligned with the center of the circle (a a fine guide line will appear between the cursor and the center point of the circle – if you don’t see it make sure your smart guides are turned on View > Smart Guides or CTRL + u (Windows) / CMD + u (Mac) ).  Drag out your rectangle so overlaps the circle on both sides.
    using smart guides and overlapping a rectangle over the circle shape
  3. With the selection tool, drag a marquee selection to select both objects
  4. From the pathfinder palette, choose the Divide option.
    using the pathfinder panel to create a half-circle in illustrator
  5.  Ungroup the resulting object (right-click and choose ungroup from the context menu).
    ungroup the grouped object created by the pathfinder palette
  6. Select and delete the remainder of the rectangle and you will be left with two perfect semi-circles. (I moved them slightly apart for illustration purposes)
    half-circle created using pathfinder divide

Method 6: Using the Shape Builder Tool

  1. Create a perfect circle by choosing the ellipse tool and then click and shift drag to constrain the tool to make the shape the same width and height.
  2. Draw out a rectangle that overlaps half the circle. Make sure to start drawing level with the anchor point on the side of the circle and watch for the smart guide to show that you are level with the center of the circle.
    using smart guides and overlapping a rectangle over the circle shape
  3. Using the Selection Tool drag a marquee around both shapes so they are both selected
    select both the circle and the overlapping rectangle
  4. Select the Shape Builder Tool and then Alt + Click (Windows) or Opt + Click (Mac) to subtract half the circle and the remainder of the rectangle. By default the shape builder tool wants to add things together so we need to use the modifying keys to set it to subtract the extra piece we don’t need instead.
    removing extaneous rectangle with the shape builder tool
  5. This leaves you with both a half circle and the original full circle.
    half-circle made with illustrator's shape builder tool

Before You Go…

Mastering the techniques for creating half circles in Illustrator is a valuable skill that can be applied to many other shapes. Whether you’re working on logos, illustrations, or any other design project, the ability to create precise and symmetrical shapes is essential. By experimenting with the different methods outlined in this article, you’ll not only be able to create perfect half circles but also gain a deeper understanding of Illustrator’s tools and capabilities. So, take the time to practice and explore the possibilities. You’ll be amazed at what you can create once you’ve mastered the techniques of making half circles.

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