Longer sheets mean fewer butt joints, but need two people.
Room 1
For corner bead.
Advanced options
Coverage in ft² per gallon of premixed compound.
This drywall calculator works out sheets, joint compound, tape, screws and corner bead — tracking walls and ceilings separately, because ceilings need half again as many screws.
The short answer
Wall area is perimeter × height, less doors and windows. Add 12% waste and divide by 32 for 4 × 8 sheets.
A 14 × 12 ft room with 8 ft walls, one door and two windows is 371 ft² of board — 13 sheets, one 4.5 gallon pail of compound, one roll of tape and about 2 lb of screws.
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How to use this drywall calculator
Enter the room and the calculator returns a full material list. Four modes:
- Room — length, width, wall height, plus doors, windows and outside corners
- Walls only — total wall run and height, for partial jobs
- Ceiling only — overhead area on its own
- Known area — separate wall and ceiling square footage
The header toggle switches between walls only and walls plus ceiling. That matters more than it sounds: ceilings take about 50% more screws than walls because the field spacing tightens, and the calculator counts them separately rather than applying one blended rate.
Under Advanced options: sheet size, finish level, pail and tape roll sizes, waste, opening areas and price.
The drywall formula
1. Wall area = Perimeter × Height
2. Board area = Wall area − openings + ceiling
3. Sheets = Board area × (1 + waste) ÷ sheet coverage
Perimeter = 2 × (Length + Width) · a 4 × 8 sheet covers 32 ft²
Worked example — 14 × 12 ft room, 8 ft walls, 1 door, 2 windows
Add the ceiling and it rises to 539 ft² and 19 sheets.
Sheet sizes
| Sheet | Coverage | Weight, 1/2 in | When to use |
|---|---|---|---|
| 4 × 8 ft | 32 ft² | ~51 lb | DIY standard — one person can manage it |
| 4 × 9 ft | 36 ft² | ~58 lb | 9 ft ceilings, vertical hanging |
| 4 × 10 ft | 40 ft² | ~64 lb | Fewer butt joints on medium walls |
| 4 × 12 ft | 48 ft² | ~77 lb | Professional standard — fewest joints |
| 4 × 14 ft | 56 ft² | ~90 lb | Long walls, needs a crew or a lift |
The reason professionals use 12 ft board isn’t the sheet count — it’s the joints. A 12 ft wall boarded with 4 × 8 sheets has a butt joint in the middle of every course. The same wall in 4 × 12 has none.
Butt joints are the hard ones to finish invisibly, because there’s no tapered edge to recess the tape into. Every one you eliminate saves mud, sanding and the risk of a visible ridge. If you can get the sheets into the room and have a second person, longer is better.
Joint compound
The practical figure for premixed all-purpose compound at a full three-coat finish is about 100 square feet per gallon. That’s tape coat, fill coat and finish coat combined.
| Pail | Covers | 4 × 8 sheets |
|---|---|---|
| 1 gallon | ~100 ft² | 3 |
| 3.5 gallon | ~350 ft² | 11 |
| 4.5 gallon | ~450 ft² | 14 |
| 5 gallon | ~500 ft² | 16 |
Why compound figures vary by three times
Published coverage for joint compound ranges from about 90 to 280 square feet per gallon. That’s a genuine three-fold spread, and it comes down to two confusions rather than any real disagreement.
| The confusion | What’s happening |
|---|---|
| Per coat vs three coats | 280 ft² per gallon is roughly right for a single coat. Divide by three for a Level 4 finish and you get 93 ft² — which matches the practical figure almost exactly. |
| Powder weight vs premixed volume | The often-quoted 0.053 lb per ft² describes setting-type powder, not premixed mud. Powder gains volume when you add water, so pounds per square foot and gallons per square foot are not interchangeable. A 25 lb powder bag covers roughly 470 ft². |
If a coverage number seems generous, ask whether it’s per coat or for the full finish, and whether it describes powder or premixed. Both errors push the same way — toward under-ordering — and running out of mud between coats means an extra trip and a joint that dried at a different rate to its neighbours.
Finish levels
GA-214 defines six levels of drywall finish. Three matter for normal work:
| Level | Coverage | What it is | Use for |
|---|---|---|---|
| Level 3 | 140 ft²/gal | Tape plus one coat over joints and fasteners | Under texture or heavy wallcovering |
| Level 4 | 100 ft²/gal | Tape plus two coats, sanded smooth | Standard — flat and eggshell paint |
| Level 5 | 74 ft²/gal | Level 4 plus a skim coat over the entire surface | Gloss and semi-gloss, or strong side light |
Level 5 uses about 35% more compound than Level 4, because you’re coating the whole wall rather than just the joints. It’s worth specifying anywhere raking light will cross the surface — a wall beside a window, or a hallway lit from one end. Under those conditions every joint and screw dimple on a Level 4 wall telegraphs through the paint.
Screws
| Surface | Spacing | Per ft² | Per 4 × 8 sheet |
|---|---|---|---|
| Walls, 16 in framing | 12 in field, 8 in edges | 1.0 | ~32 |
| Ceilings, 16 in framing | 12 in throughout | 1.5 | ~48 |
Ceilings need half again as many because gravity is working against the board rather than with it, and sag between fasteners shows badly on a flat overhead surface. Most drywall calculators apply one blended rate; this one counts walls and ceilings separately.
A 1 lb box of 1¼ inch coarse-thread screws holds roughly 200 screws, so a 5 lb box covers about 30 sheets of wall. Use 1¼ inch for 1/2 inch board on wood framing and 1⅝ inch for 5/8 inch board.
A screw should dimple the paper without breaking it. Break the face paper and the screw has almost no holding power — it’s gripping gypsum crumb rather than paper fibre. A drywall dimpler bit or a clutch setting on the driver handles this far more consistently than trigger control.
Tape and corner bead
Tape works out at about 0.37 linear feet per square foot of board, or 38 lf per 100 ft².
| Roll | Covers |
|---|---|
| 75 ft | ~200 ft² of board |
| 250 ft | ~675 ft² |
| 500 ft | ~1,350 ft² |
Paper tape is stronger and is what professionals use on flat joints and inside corners. Mesh tape is self-adhesive and easier for beginners, but it needs setting-type compound over it rather than premixed, because it’s weaker in tension and relies on the mud for strength.
Corner bead goes on outside corners only — inside corners are taped. Standard pieces are 8 ft, so count your outside corners, multiply by wall height and divide by 8.
Board thickness
| Thickness | Where | Notes |
|---|---|---|
| 1/2 in | Standard walls | The default for residential interior walls |
| 5/8 in | Ceilings, garage separation walls | Required on 24 in framing; resists sag on ceilings |
| 5/8 in Type X | Fire-rated assemblies | Code-required on the garage-to-house wall and ceiling |
| 1/4 in | Curved walls, skim over existing | Too weak to span framing on its own |
| Moisture-resistant | Bathrooms, laundry | Not a tile backer — use cement board in wet areas |
The wall separating an attached garage from living space, and the ceiling below habitable rooms above a garage, must be fire-rated — typically 5/8 in Type X. This is an inspected item and not a matter of preference. Check your local code, because requirements vary on whether the whole garage or only the separation needs it.
Sheets by room size
8 ft walls, one door and two windows, walls only, 12% waste.
| Room | Board area | 4 × 8 sheets | 4 × 12 sheets |
|---|---|---|---|
| 10 × 10 ft | 275 ft² | 10 | 7 |
| 12 × 12 ft | 339 ft² | 12 | 8 |
| 12 × 14 ft | 371 ft² | 13 | 9 |
| 14 × 16 ft | 435 ft² | 16 | 11 |
| 16 × 20 ft | 531 ft² | 19 | 13 |
| 20 × 20 ft | 595 ft² | 21 | 14 |
Hang it horizontally
On standard 8 ft walls, two courses of 4 ft board run horizontally is the right approach, and it’s what professionals do. Three reasons:
- Less joint length. A 12 ft wall hung horizontally has one 12 ft seam. Hung vertically it has two 8 ft seams — 33% more joint to tape and finish.
- Tapered edges meet. The long edges of a sheet are recessed so tape and mud sit flush. Hung horizontally, those tapered edges meet each other. Hung vertically, you get full-thickness butt joints that have to be built out and feathered wide.
- The seam is at a workable height. A horizontal joint sits at 4 ft — comfortable to tape standing up, and it crosses your eye line where light is less raking than at floor or ceiling level.
Vertical hanging makes sense on walls taller than 8 ft where a horizontal joint would land awkwardly, and in narrow spaces where you can’t manoeuvre a sheet sideways.
Drywall estimating mistakes to avoid
- Calculating from floor area. Wall surface is perimeter × height, usually three to four times the floor area.
- Under-ordering compound. Three coats needs three times what one coat suggests.
- One screw rate for everything. Ceilings need 50% more than walls.
- 1/2 in board on 24 in ceiling joists. It sags. Use 5/8 in.
- Standard board on the garage wall. Fire rating is code and it’s inspected.
- Hanging vertically on 8 ft walls. More joints, and the hard kind.
- Mesh tape with premixed mud. Mesh needs setting-type compound for strength.
Frequently asked questions
How many sheets of drywall do I need?
Multiply room perimeter by wall height, subtract doors and windows, add the ceiling if you’re boarding it, then add 12% waste and divide by 32 for 4 × 8 sheets. A 14 × 12 ft room with 8 ft walls needs 13 sheets for the walls alone, or 19 with the ceiling.
How much joint compound do I need?
About 1 gallon per 100 square feet of board for a full three-coat Level 4 finish, so a 4.5 gallon pail covers roughly 450 ft² or 14 sheets. Level 5 needs about 35% more because it includes a skim coat over the whole surface.
Why do compound coverage figures vary so much?
Two reasons. Some sources quote coverage per coat — around 280 ft² per gallon — which divided by three coats gives the practical 93 ft². Others quote 0.053 lb per ft², which describes setting-type powder rather than premixed mud; powder gains volume with water, so the two units aren’t interchangeable.
How many screws per sheet of drywall?
About 32 for a 4 × 8 sheet on walls, and roughly 48 on ceilings where the field spacing tightens to 12 inches throughout. That’s 1.0 and 1.5 screws per square foot respectively. A 1 lb box holds around 200 screws.
How much drywall tape do I need?
About 0.37 linear feet per square foot of board, or 38 ft per 100 ft². A 250 ft roll covers roughly 675 ft² of drywall and a 500 ft roll about 1,350 ft². Most single rooms need one roll.
Should drywall be hung horizontally or vertically?
Horizontally on standard 8 ft walls. It produces about a third less joint length, the tapered edges meet each other so joints finish flat, and the seam lands at a comfortable 4 ft working height. Vertical hanging creates full-thickness butt joints that are much harder to finish invisibly.
What thickness drywall should I use?
1/2 inch for standard walls, 5/8 inch for ceilings and anywhere framing is at 24 inch centres. 5/8 inch Type X is code-required on the wall between an attached garage and living space. Moisture-resistant board suits bathrooms but is not a tile backer — use cement board in wet areas.
What is a Level 5 drywall finish?
Level 4 plus a thin skim coat of compound across the entire surface, not just joints and fasteners. It uses about 35% more mud and is specified for gloss or semi-gloss paint, and for any wall crossed by strong side light where joints would otherwise telegraph through.
Do I subtract doors and windows?
Yes — drywall openings are large enough to matter. A standard interior door is about 21 ft² and a typical window 12 ft². A room with one door and two windows loses 45 ft², more than a full sheet.
Should I use 4×8 or 4×12 sheets?
4 × 12 if you can handle them — they eliminate butt joints on walls up to 12 ft, which is where most of the finishing difficulty lies. But a 4 × 12 half-inch sheet weighs about 77 lb and needs two people. 4 × 8 is the practical DIY choice.
How much waste should I add?
10% for a simple rectangular room with few openings, 12% for a typical room with closets and several doors and windows, and 15% or more for complex layouts with angled walls or soffits.
Paper tape or mesh tape?
Paper is stronger and is what professionals use on flat joints and inside corners. Mesh is self-adhesive and more forgiving for beginners, but it must be coated with setting-type compound rather than premixed, because it relies on the mud for tensile strength.
Standards and sources
- ASTM C840 — Standard specification for application and finishing of gypsum board
- GA-216 — Gypsum Association application and finishing standards, including fastener spacing
- GA-214 — Recommended levels of gypsum board finish
- Compound coverage figures are for premixed all-purpose at a full three-coat finish; powder products are measured by weight and are not directly comparable
- Sheet weights and screw counts from manufacturer packaging data
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How this drywall calculator works out its numbers
Wall area is perimeter times height less the openings you enter; ceiling area is length times width and is tracked separately throughout. Sheets are total board area times the waste factor, divided by sheet coverage and rounded up.
Screws are calculated at 1.0 per square foot on walls and 1.5 on ceilings, reflecting the tighter 12 inch field spacing overhead — that works out to about 32 and 48 per 4 × 8 sheet respectively. Compound uses coverage per gallon for a full three-coat finish at your chosen level, not per coat. Tape uses 0.37 linear feet per square foot of board. Corner bead is outside corners times wall height, divided into 8 ft pieces.
Coverage figures are planning estimates. Actual compound use varies considerably with joint density, how heavily you apply each coat, and how much you sand back. Fastener spacing, board thickness and fire-rated assemblies are governed by your local building code and by ASTM C840 — particularly the garage separation wall, which is an inspected item.