How to Draw a Perfect Circle Selection in GIMP

To draw an ellipse selection constrained strictly to a 1:1 aspect ratio in GIMP, you use the Shift key. However, the order in which you press the key matters to avoid triggering selection modes. This guide explains how to use modifier keys properly to draw a perfect circle selection, along with built-in tool settings for persistent 1:1 constraints.

Using the Shift Modifier Key

  1. Activate the Tool: Select the Ellipse Select Tool from the Toolbox or press the shortcut key E.
  2. Click and Drag First: Click on the canvas and begin dragging to define the selection area.
  3. Hold Shift: While holding down the left mouse button, press and hold the Shift key. The ellipse will instantly snap to a 1:1 square aspect ratio, forming a perfect circle.
  4. Release Mouse First: Release the left mouse button to set the selection, then release the Shift key.

Note: You must start dragging before pressing Shift. If you press Shift before clicking, GIMP interprets the action as the "Add to current selection" mode rather than an aspect ratio constraint.

Drawing from the Center Outward (Shift + Ctrl)

If you want the circle to expand outward from its center point rather than from a corner:

  1. Click and begin dragging from the desired center point.
  2. Press and hold both Shift and Ctrl simultaneously.
  3. Adjust the size to your liking.
  4. Release the mouse button first, followed by the modifier keys.

Alternative Method: Fixed Aspect Ratio in Tool Options

If you prefer not to rely on keyboard modifiers, you can permanently lock the tool to a 1:1 ratio via the interface:

  1. Open the Tool Options dockable dialog with the Ellipse Select Tool active.
  2. Check the box labeled Fixed.
  3. Ensure the dropdown menu is set to Aspect ratio.
  4. Enter 1:1 into the text field below the dropdown.

With this option enabled, every ellipse selection you draw will automatically be constrained to a perfect circle without needing to hold any modifier keys.