Change canvas size in Photoshop (borders, side extensions, relative vs. absolute)
This guide walks you through changing canvas size in Photoshop. You’ll add an even border, extend the canvas on one side only, pick an extension color, and understand the difference between Relative and absolute sizing.
Step-by-step instructions
Open the Canvas Size dialog
Go to Image → Canvas Size.
Shortcut: Alt+Ctrl+C (Windows) or Option+Cmd+C (Mac).
Add an even border around the image
In Canvas Size, enable Relative.
Set Width and Height to 5 in (or your desired border size).
Set Canvas extension color to White (or another color), then click OK.
Extend canvas on one side only
Open Image → Canvas Size again.
Choose units (Pixels or Percent); for example, Percent.
Click the Anchor grid to pin to the left so the empty space appears on the right.
Adjust Width (e.g., 10% or 100% for a larger area).
Set Canvas extension color (e.g., Gray), then click OK.
Understand Relative vs. absolute sizing
Relative checked: the values you enter are added to the current canvas size (e.g., +55 px on each side when anchored center).
Relative unchecked: the values set the total final canvas size (e.g., Width = 55 px total).
