Drywall for a 18 × 16 ft ceiling: ⅝″ 4 × 12 on 16″ joists

Ceiling boards

7× ⅝″ 4 × 12 ft

288 ft² ceiling plus 12% — framing at 16″ o.c.

Boards12% waste — ceilings cut around fixtures	7⅝″ 4 × 12 ft
Ceiling area18 × 16 ft	288ft²
Sag check⅝″ 4 × 12 ft is rated for framing at 16″ o.c.	OK
Screws12″ spacing on ceilings, not 16″ — about 1 lb box	404screws
Joint compound	0.74.5 gal buckets
Paper tape	134linear ft
Weight per boardoverhead — a panel lift is worth the hire, and it is not optional on ⅝″ 12 ft boards	105lb
Fixture cut-outscut after the board is up, from the joist positions marked on the floor	2holes

Length: 18 ft
Width: 16 ft
Board: ⅝″ 4 × 12
Joist spacing: 16 in o.c.
Light fittings: 2

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 404 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

7 boards of ⅝″ 4 × 12, 0.7 buckets of compound, 134 linear ft of tape.

Waste is 12% rather than the 10% used on walls, because a ceiling gets cut around 2 light fitting2 plus vents and the perimeter.

Each board weighs 105 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 × 12 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 105 lb overhead. At this weight a panel lift is not a convenience, it is the difference between doing the job and dropping a board on someone.
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 2 lights, plus any fan boxes, vents and the perimeter.

Nearby sizes

Cost to Repair a Drywall Ceiling: Patch, Section, or Take It DownA twelve-inch patch and a whole ceiling are not on the same price curve. The patch is three visits and a texture match; the ceiling is one day and no matching at all.
All-Purpose or Lightweight Joint Compound: Where Each One BelongsLightweight sands better, shrinks less and dries faster. It also bonds less, which is why the bedding coat is the one place it does not belong.
Cost to Drywall a Room by Size: Six Rooms Priced Line by LineRooms are quoted by floor area and built by wall area, and the two scale differently. A room twice the floor size needs far less than twice the drywall.
DIY Drywall or Hire It Out: The Real Saving, Tools and Calendar IncludedThe material-versus-quote gap looks enormous. Subtract the tools, the rental and the fact that finishing is a skill, and the honest saving is smaller and still worth having.