Horizontal or vertical, and why it is not a preference
Drywall sheets have two long tapered edges and two square-cut ends. The tapered edges are there so that when two of them meet, the recess holds the tape and two coats of compound and finishes flush with the surface. Where two square ends meet, there is no recess. The tape and mud sit proud of the wall, and the only way to hide that is to build the compound out in a wide, shallow mound eighteen inches or more across. That is a butt joint, and it is the thing that separates a wall that looks flat from one that shows every seam when the sun comes in low.
Hanging horizontally, with the sheets lying flat and running the length of the wall, puts one continuous tapered seam across the room at the four foot line and pushes the butt joints out to wherever the sheets end — every 8, 10 or 12 feet. Hanging vertically, sheets stood on end, puts a tapered seam every four feet from floor to ceiling and no butt joints at all on a wall shorter than the sheet.
The linear footage is often close. On an 8 foot wall with 8 foot sheets it is identical. What differs is where the joints are and what kind they are. Horizontal wins for most rooms because it produces fewer butt joints, puts the main seam at chest height where it is easy to finish standing up, and bridges slight variations between studs. Vertical earns its place on walls taller than your longest sheet, in stairwells and narrow spaces where you cannot manoeuvre a sheet flat, and where a fire-rated assembly specifies the sheet edges land on framing.
| Horizontal | Vertical | |
|---|---|---|
| Tapered joints | One long run per wall | Every 4 ft, floor to ceiling |
| Butt joints | Every sheet length | None, if the sheet reaches the ceiling |
| Working height | Seam at about 4 ft | Full-height seams |
| Handling | Needs two people or a lift | Manageable alone |
Where the screw, tape and compound numbers come from
The screw count here is not a rule of thumb. A 4 foot wide sheet crosses four framing members at 16 inch centres and three at 24 inch. Along each of those, screws go in at roughly 16 inches on walls and 12 inches on ceilings, so an 8 foot sheet takes seven fixings per stud on a wall and nine per joist on a ceiling. That is 28 screws per sheet on the wall and 36 on the ceiling at 16 inch centres. Fastener schedules vary between the building code, the board manufacturer and whether adhesive is used, and perimeter fastening is usually tighter than field fastening, so treat this as the working figure and check the schedule if the job is inspected. Screws are counted at about 320 per pound for 1-1/4 inch coarse thread, which is close for most brands and not exact for any of them.
Tape is worked out from the joint layout rather than a rate. Every sheet contributes joint along the edges it shares, the four inside corners of the room take tape floor to ceiling, and the wall-to-ceiling line takes tape all the way round. For a 12 by 14 room with 8 foot ceilings and 4x8 sheets that comes to about 230 feet, which works out near the old rule of 370 feet per 1000 square feet of board once you remember that the rule usually excludes corners. What the number does not include is corner bead. Outside corners are not taped, they are beaded, and bead is bought by the stick and counted per corner.
Joint compound is the loosest of the three, because it depends more on the person holding the knife than on the room. The rates used here are the common working figures: roughly a gallon per 125 square feet of board for a level 3 finish, per 100 square feet for level 4, and per 70 square feet for level 5. A 4.5 gallon bucket therefore covers somewhere around 450 square feet at level 4, which matches the 400 to 500 square feet most suppliers quote. Those figures exclude setting-type compound if you use it for the first fill, exclude texture, and exclude the material you sand off. A first-timer will use noticeably more than this and should buy an extra bucket.
Finish levels, briefly, because they change the mud by half
Level 3 is tape plus two coats over joints and fasteners, intended to disappear under a heavy texture or a wall covering. Level 4 is tape plus three coats and is the normal specification for a flat or eggshell painted wall. Level 5 adds a thin skim coat over the entire surface, which is what you want under gloss paint or in a room with strong raking light, because at level 4 the compounded areas and the bare paper take paint differently and the joints show as bands. The jump from level 4 to level 5 is not a small amount of extra mud, it is roughly forty percent more, plus the labour of skimming every square foot.
Order the awkward things at the same time
The sheet count is what people phone in and it is the part least likely to be wrong. Make the order include the rest of it: corner bead by the stick with a count of outside corners, at least one more roll of tape than the calculator says, an extra bucket of compound, and a box of screws longer than you think you need if the ceiling gets a second layer. Delivery is the expensive part of a drywall order, and going back for one item costs more in time than buying the whole lot twice over. If the sheets are being delivered, have them put inside the room they are going in rather than in the garage — twelve foot sheets do not turn corners, and moving fifty of them by hand a second time is a genuinely bad day.
Questions people ask
How many sheets of drywall for a 12 by 14 room?
With 8 foot ceilings the walls are 2 x (12 + 14) x 8, which is 416 square feet, and the ceiling is 168, for 584 square feet in total. At 32 square feet per 4x8 sheet that is 19 sheets with no waste allowance and no deduction for openings. Add 10 percent for waste and take half credit for a door and two windows and you land near 20. Going to 4x12 sheets drops it to about 14 and cuts the number of butt joints by more than half, which matters more for the finish than the sheet count does for the price.
How much joint compound do I need per sheet?
About a third of a gallon per 4x8 sheet at a level 4 finish, which is the standard for a painted wall. That is the common working rate of roughly a gallon per 100 square feet of board, and a 4.5 gallon bucket covering somewhere between 400 and 500 square feet. The spread is wide because it depends on how heavily you load the knife, how much you sand back, and whether the framing is flat enough that the joints need building out. First time through, buy an extra bucket. Compound keeps if the lid is sealed and it is not allowed to freeze.
Should I use 1/2 inch or 5/8 inch drywall?
Half inch is standard for walls in a house. Five-eighths is used on ceilings, particularly over joists at 24 inch centres where half inch will sag over time, and it is required in various fire-rated assemblies such as a garage ceiling under living space or a shared wall between dwellings. It is also noticeably better at sound. The trade-off is weight: a 4x8 sheet of 5/8 is about 70 pounds against 50 for half inch, and lifting that overhead is the difference between a job with a drywall lift and a job without one. Which one you need in a specific location is set by your local code, not by preference.
Does the calculator account for cutting around outlets and windows?
Only through the waste allowance and the opening deduction, and those are blunt instruments. Cutouts for boxes produce no usable offcut and take no extra board. Openings are different: the calculator lets you take no credit, half credit or full credit, and half is closest to what actually happens, because the strip above a door is short and the returns beside a window are narrow, so most of that board goes in the skip rather than onto another wall. If the room has a lot of small openings, take no credit at all and let the extra sheets be your margin.