MudAndTapeSheets, mud, tape and screws for a room, with the waste counted.

Drywall for a 20 × 18 ft ceiling: ⅝″ 4 × 8 on 16″ joists

Ceiling boards
13× ⅝″ 4 × 8 ft
360 ft² ceiling plus 12% — framing at 16″ o.c.
Ceiling planboards run across the joists · joists at 16″ o.c.13× ⅝″ 4 × 8 ft504 screws at 12″70 lb per boardSag: OK
Boards12% waste — ceilings cut around fixtures13⅝″ 4 × 8 ft
Ceiling area20 × 18 ft360ft²
Sag check⅝″ 4 × 8 ft is rated for framing at 16″ o.c.OK
Screws12″ spacing on ceilings, not 16″ — about 1 lb box504screws
Joint compound0.84.5 gal buckets
Paper tape166linear ft
Weight per boardoverhead — a panel lift is worth the hire, and it is not optional on ⅝″ 12 ft boards70lb
Fixture cut-outscut after the board is up, from the joist positions marked on the floor4holes
Length
20 ft
Width
18 ft
Board
⅝″ 4 × 8
Joist spacing
16 in o.c.
Light fittings
4

A ceiling is not a wall lying down

Three things change, and all three are in the standards rather than in preference.

Thickness depends on framing spacing. ½″ standard board sags between joists at 24″ on center — it looks fine for a season and then develops a slow wave that no skim coat corrects. At 24″ you want ⅝″, or ½″ sag-resistant board rated for it.

Sag check for this ceiling: OK.

Screws every 12 inches, not 16. A ceiling board fights gravity for its whole life; a wall board rests on the plate. That is 504 screws here.

Boards run perpendicular to the joists. A board bridging several joists is far stiffer than one running along a single bay, and it spreads load across the joints instead of concentrating it.

What to buy

13 boards of ⅝″ 4 × 8, 0.8 buckets of compound, 166 linear ft of tape.

Waste is 12% rather than the 10% used on walls, because a ceiling gets cut around 4 light fitting4 plus vents and the perimeter.

Each board weighs 70 lb, overhead

A panel lift is worth the hire. On the heavier boards it is not a convenience — it is the difference between doing the job and dropping a board on somebody.

Mark the joists on the floor first

Once a board is up you cannot see the framing, and hunting for it with a screw gun leaves a ceiling full of holes that all have to be filled.

Notes

  • ⅝″ 4 × 8 ft is rated for 16″ framing. Note it is the **board** that carries the rating, not the paint or the texture over it.
  • **Screws every 12 inches on a ceiling**, not 16. A ceiling board fights gravity for its whole life; a wall board rests on the plate. That difference is why ceiling screw patterns are tighter, and why a ceiling that was screwed to wall spacing shows fastener pops first.
  • Run the boards **perpendicular to the joists**. A board bridging several joists is far stiffer than one running along a single bay, and it spreads the load across the joints instead of concentrating it.
  • Each board weighs 70 lb overhead. Two people can manage it, but a panel lift makes the joints tighter because nobody is fighting the weight while positioning.
  • Mark the joist positions on the floor before you lift a board. Once it is up you cannot see them, and hunting for framing with a screw gun leaves a ceiling full of holes.
  • 12% waste rather than the 10% used on walls — ceilings are cut around 4 lights, plus any fan boxes, vents and the perimeter.

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