Understanding your result
The headline is the total number of sheets, and the line under it splits them into the three surfaces a garage has: the ceiling, the wall shared with the house, and the other walls. Each surface gets its own line in the table with the board type the code calls for, because a garage order is often two kinds of board, type X for the ceiling and regular for the walls, and the two are priced and stocked differently.
The “Type X or 5/8 in” tile is the number of heavier sheets in the order. With living space above the garage it is the whole ceiling in 5/8 in type X. Without, it is still the ceiling when the trusses are 24 in apart, because regular 1/2 in board sags at that spacing; the calculator says which reason applies. The screws, compound and tape follow the sheet count, with the compound at the finish level you chose: a fire-taped garage (Level 2) needs about half the compound of a painted one.
The notes carry the code language in plain words. They are a summary of the International Residential Code, not your local amendment, and the fire-rated drywall calculator goes further when a one- or two-hour wall is actually required, for example between a garage and a dwelling unit in a duplex. For a garage with no fire question at all, the room sheet calculator gives the same count without the split.
How we calculate this
Each surface is rounded up separately, because the ceiling and the walls are different board. The sheet areas are on the sheet sizes page. The house door is taken out of the shared wall rather than the other walls, since that is where it is, and garage doors come out of the other walls at the area you give per door: 63 sq ft for a 9 × 7 ft door, 112 sq ft for a 16 × 7 ft double door.
Screws use the GA-216 pattern with walls at 16 in on centre and the ceiling at the joist spacing you chose, 12 in along each joist; the screw calculator handles 24 in wall framing and 1-5/8 in screws for 5/8 in board. Compound is the GA-214 finish level you chose: Level 2 for fire taping, which is the common garage finish, or Level 4 for a painted garage; the joint compound calculator takes the sheet count from here if you want setting-type compound instead.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Garage-house wall | 1/2 in gypsum board minimum on the garage side | International Residential Code R302.6, Table R302.6 |
| Garage ceiling under habitable rooms | 5/8 in type X | IRC Table R302.6 |
| Structure supporting that ceiling | 1/2 in gypsum board | IRC Table R302.6 |
| Door between garage and house | Solid wood 1-3/8 in, solid or honeycomb steel 1-3/8 in, or 20-minute rated | IRC R302.5.1 |
| Regular 1/2 in board on 24 in joists | Not used; 5/8 in or sag-resistant 1/2 in | Our choice: IRC Table R702.3.5 allows 1/2 in across 24 in joists, but it sags more than heavier board |
| Garage door opening | 63 sq ft (9 × 7 ft) per door | Common residential door size; a 16 × 7 ft double is 112 sq ft |
| Finish | Level 2 (fire taping) | Gypsum Association GA-214 levels; see the levels table |
| Waste | 10% | Garages are plain rectangles with large openings |
Assumptions last reviewed October 8, 2026.
The calculator summarises the model code. Local codes add to it: some require 5/8 in type X on the house wall, some require board on every garage wall, some treat a garage with a gas appliance differently. It does not model a fire-rated assembly as a whole (fastener spacing, joint treatment and insulation are part of a rated listing), which is what the guide to fire-rated assemblies and the garage fire-separation guide explain before you buy.
Two worked examples
A 22 × 22 ft attached garage with a bedroom above and one 16 ft door
Ten-foot walls, a 22 ft wall shared with the house, one 16 × 7 ft garage door (112 sq ft), one entry door, one window, 16 in joists, painted finish (Level 4), 4 × 8 sheets.
- Gross wall area: 2 × (22 + 22) × 10 = 880 sq ft
- House wall: 22 × 10 − 20 = 200 sq ft → 200 ÷ 32 × 1.1 = 6.9, rounded up to 7 sheets (1/2 in minimum)
- Other walls: 880 − 220 − 127 = 533 sq ft → 19 sheets of 1/2 in
- Ceiling: 22 × 22 = 484 sq ft → 17 sheets of 5/8 in type X, because of the bedroom above
- 43 sheets, 1,323 screws (6.3 lb), 11.4 gallons of compound (3 pails), 584 ft of joints (2 rolls)
The 17 type X sheets are the heavy part of the order, 70 lb each, and they are the surface the inspector will look at: taped and filled, with no gaps at the walls.
A 20 × 20 ft detached garage with 24 in trusses, fire-taped
Eight-foot walls, one 9 × 7 ft door, one entry door, two windows, ceiling boarded, Level 2 finish, 4 × 8 sheets.
- Gross wall area: 2 × (20 + 20) × 8 = 640 sq ft; openings 63 + 20 + 30 = 113 sq ft; 527 sq ft → 19 sheets
- Ceiling: 400 sq ft → 14 sheets of 5/8 in, not for fire but because the trusses are 24 in apart
- 33 sheets, 882 screws (4.2 lb), 3.9 gallons of compound (1 pail), 460 ft of joints
No shared wall, so no separation rule, and the Level 2 finish needs one pail. The ceiling screw pattern on 24 in trusses is 25 per sheet instead of 35, which the arithmetic line shows.
Where to find your inputs
Shared wall length. Walk the inside of the garage and measure every wall that has the house on the other side, including a wall under a bedroom bump-out. If the house wraps two sides of the garage, add them.
Living space above. Any habitable room: bedroom, office, bonus room. An attic used for storage is not, but check the floor-ceiling assembly rules with your inspector if the attic has a floor.
Garage doors. Use the door size on the opener’s paperwork or measure the opening: single doors are usually 8 or 9 ft wide, doubles 16 ft, all 7 ft tall in most houses, 8 ft in newer ones.
Joist spacing. Look up: trusses are almost always 24 in on centre; dimensional joists in older garages are 16 in. The thickness selector turns that into a board choice for any ceiling.
Common mistakes
- Regular 1/2 in on 24 in trusses. The most common garage ceiling failure, visible within a year as waves between the trusses.
- Type X on the walls, regular on the ceiling. Backwards. The ceiling under living space is where type X is required; the house wall needs 1/2 in minimum.
- Leaving gaps at the top of the house wall. The separation must be continuous: board the wall to the ceiling, fire-caulk the penetrations, and cover the framing that supports the ceiling.
- A hollow-core door to the house. It fails the inspection. Solid wood 1-3/8 in, solid steel, or a 20-minute rated door, self-closing where your code says so.
- Painting without taping. Fire taping is tape plus one coat, nothing less. Untaped joints void the separation.
- Ducts in the garage. Any duct in the garage must be 26-gauge steel with no openings into the garage; it is not drywall, but it fails the same inspection.
Questions people ask
- What drywall does an attached garage need?
- Under IRC R302.6, at least 1/2 in gypsum board on the garage side of the wall shared with the house, 5/8 in type X on the garage ceiling if there are habitable rooms above it, and 1/2 in board on the framing that supports that ceiling. The other garage walls have no requirement unless they are close to a property line.
- How many sheets of drywall for a 24 × 24 ft garage?
- With 9 ft walls, two 9 × 7 ft doors, one entry door, one window and the ceiling boarded, about 45 sheets of 4 × 8 at 10% waste: 20 for the ceiling, 7 for the house wall and 18 for the other walls. Trusses at 24 in put 5/8 in board on the ceiling; the walls can be 1/2 in.
- Do I need 5/8 in type X on the garage ceiling?
- Only when there is living space above it. Then the whole ceiling is 5/8 in type X, with the joints taped and the screw heads covered even if you never paint it. With nothing above, the ceiling can be 1/2 in, but garage trusses are usually 24 in apart, where regular 1/2 in sags, so 5/8 in is the practical choice there too.
- Does a detached garage need fire-rated drywall?
- Not under the IRC's garage separation rule, which applies to attached garages. A detached garage within 3 ft of the house or another building has exterior-wall fire-rating rules of its own, and some jurisdictions require board on any garage with a heater; check locally before you buy.
- How much joint compound for fire taping a garage?
- A Level 2 finish, tape embedded and one coat over the joints and fastener heads, uses about 0.42 gallons per 100 sq ft, less than half of a painted Level 4 finish. A 24 × 24 ft garage with 1,280 sq ft of board needs about 5.4 gallons, two pails, instead of 12 gallons for a painted finish.
- What about the door between the garage and the house?
- IRC R302.5 requires a solid wood door at least 1-3/8 in thick, a solid or honeycomb-core steel door of the same thickness, or a 20-minute fire-rated door, and no door directly into a bedroom. The door is not drywall, but it is part of the same separation, and it is a common inspection failure.