What mud ring means
A mud ring is the raised cover on a square metal box that brings the opening out flush with the drywall and gives the device a mounting point.
Also called plaster ring, device ring.
Where it matters on a electrical job
Ring depth has to match the wall finish, and a ring marked with its volume adds to the box fill. Order the right depth for the drywall or paneling thickness before rough-in.
What the model code says
- Plaster rings and extension rings marked with their volume count toward the box's volume. (IRC 2021, Chapter 39)
Check which code edition your building department enforces for mud ring before you quote.
Work it out
- Free calculator: Box fill calculator
- Licensing: Electrical license rules by state
- Tools, templates and guides: Free electrical resources
Sources: 2021 International Residential Code, Chapter 39, Power and Lighting Distribution (ICC). Checked October 9, 2026.