How to Measure Radius in Illustrator?

In Adobe Illustrator, the most precise way to measure the radius of a circle is by using the Measure Tool to determine the distance from the circle's center point to any point on its edge.

Using the Measure Tool to Find Radius

The Measure Tool (Measure Tool (M)) is specifically designed for calculating distances within your artwork. Measuring the radius of a circle with this tool is straightforward once you identify the key points.

• Reference: By default, Illustrator will start measuring from the circle's center, so all we need to do is to click somewhere along the edge to find the radius value.

This means you initiate the measurement from the center and end it at the circumference.

Step-by-Step Guide

Follow these steps to measure your circle's radius:

1. Select Your Circle: Click on the circle object you wish to measure using the Selection Tool (V).
2. Activate the Measure Tool: Find the Measure Tool in your Tools panel. It is often grouped with the Eyedropper Tool.
   • Note: If you can't see it, right-click the Eyedropper Tool icon to expand the nested tools.
3. Locate the Center: Hover your cursor over the center of the circle. If you have Smart Guides (View > Smart Guides, shortcut Cmd+U or Ctrl+U) enabled, Illustrator will usually snap to or highlight the center point.
4. Start the Measurement: Click once precisely on the center of the circle.
5. End the Measurement: Move your cursor from the center towards the edge of the circle. Click a second time exactly on the path of the circle's edge.

Viewing the Measurement Result

After performing the second click on the edge, the distance between the two points (the center and the edge) will be displayed.

• Look at the Info panel (Window > Info). This panel shows detailed information about selections and measurements. The D value (Distance) shown in the Info panel represents the length of the line you just measured – which is the radius of your circle.

Why This Method Works

This technique leverages the fundamental definition of a circle's radius. By using the Measure Tool to click from the center to the edge, you are directly calculating that specific distance. The Info panel then provides you with the exact numerical value of this measurement.

Alternative Way to See Dimensions (Diameter)

While not a direct radius measurement, you can also quickly see a circle's overall size which relates to its diameter:

• Properties Panel: With the circle selected, the Properties panel (Window > Properties) displays the Width and Height under the Transform section. For a perfect circle, these values are identical and represent the diameter. The radius is half of this value.

Using the Measure Tool as described, starting from the center and clicking the edge, remains the method specifically designed to directly provide the radius measurement within Illustrator.

Table: Finding the Measure Tool