For projects that require a corner radius or laying out a diameter, I’ve always found it a challenge. I never had anything that matched the exact radius. An easier way is to make and use a set of simple templates.
They’re made from two layers of 1⁄8” hardboard. The bottom layer forms right-angle “fences” that register against the corner of the workpiece for drawing a radius. The top is drilled with a hole sized to match the diameter needed and acts as a circle template.