Drywall Calculator
Work out how many drywall sheets a room needs, plus the joint compound, tape and screws, and why deducting doors and windows is a false economy.
Wall perimeter × ceiling height, plus the ceiling if you are boarding it.
10-15% covers offcuts around doors and windows.
Longer sheets mean fewer butt joints to tape, but they are far harder to handle alone.
Do not deduct doors and windows. The offcuts around an opening are rarely reusable, so the allowance and the deduction cancel out — and running short mid-hang is worse than a spare sheet.
What this calculator does
Drywall is cheap and hanging it is unpleasant, which makes running short the worst possible outcome — you stop mid-job, drive to the store, and come back to finish a wall that now has a seam you did not plan. This calculator sizes the sheets and the three consumables people reliably forget: compound, tape and screws.
The sheet calculation
Drywall is four feet wide always; the name gives the length:
| Sheet | Coverage |
|---|---|
| 4 × 8 ft | 32 sq ft |
| 4 × 10 ft | 40 sq ft |
| 4 × 12 ft | 48 sq ft |
Measure your wall area as perimeter × ceiling height, add the ceiling separately if you are boarding it, divide by the sheet coverage and add a waste allowance of 10 to 15%.
A 12 × 14 foot room with 9-foot ceilings has 52 feet of perimeter, so 468 square feet of wall. In 4 × 8 sheets that is 14.6 sheets of bare coverage, and 17 with a 12% allowance.
Why you should not deduct openings
This is counterintuitive and it is the most common mistake.
The instinct is to subtract 21 square feet for a door and 15 for a window. The problem is what happens to the material around the opening: you cut a sheet to fit above a window and the offcut is an awkward strip that fits nowhere else. That waste is roughly the size of the opening you deducted.
Deducting openings and applying a normal waste allowance double-counts the saving, and the result is being one sheet short on the final wall. Ignore anything smaller than a garage door.
Sheet length is a finishing decision
The choice between 4 × 8 and 4 × 12 is not about material cost, it is about how much taping you sign up for.
Drywall sheets have tapered long edges, which create a shallow recess for tape and compound to sit in. The result finishes flat and invisible. The short ends are not tapered — a joint between two sheet ends is a butt joint, and it has to be built up and feathered wide to disguise the ridge.
Fewer sheets means fewer butt joints. A 4 × 12 sheet spanning a 12-foot wall has none at all. Against that, a half-inch 4 × 12 weighs around 75 pounds and is genuinely awkward for one person, particularly overhead. Buy the long sheets if you have a second pair of hands, the short ones if you do not.
The consumables
Joint compound, about a gallon per 125 square feet for a standard three-coat finish. Buy pre-mixed in the largest bucket that makes sense — it is cheaper per gallon and keeps well sealed.
Tape, roughly 400 linear feet per 1,000 square feet of board. Paper tape is stronger and standard for flats; mesh is easier for beginners but wants a setting compound over it.
Screws, about 32 per sheet on 16-inch framing. A one-pound box holds roughly 300, so a 17-sheet room needs about two pounds.
What this leaves out
- Corner bead for every outside corner, sold by the length.
- Primer, and specifically a drywall primer or sealer. Fresh compound and paper face absorb paint at completely different rates, so skipping primer produces visible flashing — the same problem covered in how much paint a room needs.
- Framing fasteners, furring and blocking, which are structure, not surface.
- Specialty board — moisture-resistant, fire-rated, or cement board behind tile. The quantity is identical, the product and price are not.
- Disposal. Drywall offcuts are bulky and heavy, and many transfer stations charge by weight.
After the board goes up
Once it is taped and sanded, the paint calculator sizes the primer and finish coats — remember new board drinks the first coat, so plan for three rather than two. If the room is getting tile over the new surface, the tile calculator handles that, and the flooring calculator covers what goes underfoot.
For application and finishing standards, including the level 1–5 finish definitions that contractors quote against, the Gypsum Association publishes GA-216, which is the document US inspectors and manufacturers reference.
How this is calculated
sheets = ceiling( area ÷ sheet coverage × (1 + waste) ) 4×8 = 32 sq ft, 4×10 = 40 sq ft, 4×12 = 48 sq ft compound ≈ 1 gallon per 125 sq ft tape ≈ 400 linear ft per 1,000 sq ft screws ≈ 32 per sheet on 16-inch framing
Frequently asked questions
- Should I subtract doors and windows?
- No, for anything smaller than a garage door. The offcuts around an opening are rarely reusable elsewhere, so the material you would save on paper is lost to waste anyway. Deducting them is how people end up one sheet short on the last wall, which is far more expensive in time than a spare sheet is in money.
- Which sheet size should I buy?
- Longer sheets mean fewer butt joints, and butt joints are the hardest to finish invisibly because there is no tapered edge to bed the tape into. A 4×12 across a 12-foot wall gives a seamless run. The trade-off is weight — a 4×12 half-inch sheet is around 75 pounds and genuinely difficult to handle alone.
- How much joint compound do I need?
- Roughly one gallon per 125 square feet of board for a standard three-coat finish. A level 5 finish, where the entire surface is skim coated, uses substantially more. Buying the larger bucket is almost always cheaper per gallon and leftovers keep well if sealed.
- Do I need different drywall in a bathroom?
- Yes for wet areas. Moisture-resistant board is standard around bathrooms, and cement board or a waterproof membrane is required behind tile in a shower. Standard board behind a shower surround will fail. Quantities are calculated the same way, only the product changes.
- What thickness should I use?
- Half inch is standard for walls and ceilings on 16-inch framing. Five-eighths is used where fire rating is required, such as garage ceilings under living space, and it sags less on ceilings with 24-inch framing. Check your local code before choosing, since the requirement is jurisdictional.