In this video, This Old House general contractor Tom Silva shares some tricks-of-the-trade for accurately marking drywall cutouts.
1. Stand level on the floor and hold it perfectly plumb against the side of the electrical box.
2. Use pencil to mark the top and bottom of the electrical box onto the level.
3. Next, draw a line along the side of the level and onto the floor.
4. Hold the level plumb against the opposite side of the electrical box, and draw a second line onto the floor.
5. Set the drywall sheet in place against the wall. Stand the level on one of the pencil lines on the floor. Plumb up the level and draw a vertical line onto the drywall sheet. This line represents one side of the electrical box.
6. Transfer the two pencil marks on the level onto the drywall, representing the top and bottom of the electrical box.
7. Now stand the level on the second pencil mark on the floor. Plumb up the level and draw a vertical line onto the drywall sheet. This represents the remaining side of the electrical box.
8. Connect the two horizontal lines on the drywall with the two vertical lines to complete the outline of the electrical box.
9. Cut along the lines with a jab saw to complete the electrical-box cutout.
10. Take a mark-and-cut transfer sheet and peel off the protective backing to expose the sticky adhesive surface.
11. Press the transfer sheet onto the electrical box.
12. Stand the drywall sheet in position against the wall. Use a rubber mallet to tap on the drywall directly over the electrical box. The outline of the box will be transferred to the rear of the drywall sheet.
13. Turn around the drywall sheet and cut along the red transfer lines.