Understanding your result
The headline is the number of sheets of 5/8 in type X, and the line under it shows how it is built: sheets per layer per side, times layers, times sides, with the screw spacing on the face layer. The tiles give the screws, the length of perimeter to seal and the weight of the board.
The table follows the listing line by line: the studs it uses, the face area, the sheets per layer, the screws per sheet at the listing’s spacing (and at 24 in for the base layers of multi-layer listings, which many of them use), the insulation if the listing includes it, and the perimeter. If you entered your own listing, the figures follow your entries.
The notes are the rules that are not numbers: tape and fill every joint, seal every gap, run the wall to the structure above, and use rated doors. For a quick count of type X sheets by location, the fire-rated drywall calculator is simpler; the soundproofing calculator lists the two-hour walls that are also sound walls; and the garage calculator handles the prescriptive garage separation, which is not an hourly listing.
How we calculate this
The presets come from GA-600: WP 3660 is one layer of 5/8 in type X each side of 2 × 6 studs at 16 in, at right angles, with 2-1/4 in screws 7 in on centre; WP 3661 adds 5-1/2 in mineral fibre and spaces the screws 12 in on centre. The two-hour preset counts the usual two layers each side and asks you for the listing’s face-layer spacing, because two-hour listings differ. The sound and fire assemblies page lists these files with their sources, and the fastener spacing table shows how listing spacing compares with ordinary spacing.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| 1-hour preset | 5/8 in type X each side, 2 × 6 studs at 16 in, screws 2-1/4 in at 7 in | Gypsum Association GA-600 file WP 3660 |
| 1-hour insulated preset | As above with 5-1/2 in mineral fibre, screws at 12 in | GA-600 file WP 3661 |
| 2-hour preset | Two layers of 5/8 in type X each side; face spacing entered | Typical of GA-600 two-hour listings; check yours |
| Base-layer screws | 24 in on centre | Common in multi-layer listings; check yours |
| Board weight | 2.2 lb per sq ft | Manufacturer data for 5/8 in type X |
| Waste | 10% | Plain walls |
Assumptions last reviewed October 8, 2026.
The calculator does not pick the listing your building needs (the code and your designer do), does not count the studs, plates, rated doors, firestop systems or joint compound, and does not cover shaft walls, area separation walls or floor-ceiling listings, which have their own details. It is a materials count for a listing you have chosen, not a design. How to read a listing, and why the screw spacing is part of the rating, is in the guide to fire-rated assemblies; the simpler garage rules are in the garage fire-separation guide.
Two worked examples
A 24 × 9 ft one-hour wall built to WP 3660
- Face area: 216 sq ft; sheets per layer: 216 ÷ 32 × 1.1 → 8
- Sheets: 8 × 1 × 2 = 16 sheets of 5/8 in type X, about 1,126 lb
- Screws: 7 studs × 7 at 7 in = 49 per sheet; 784 screws of 2-1/4 in
- Perimeter to seal: 132 ft
Seven inches is closer than the 16 in an ordinary wall gets, and it is the listing’s number: the screw gun is busy, and the inspector can count.
A 30 × 10 ft two-hour wall, face layer screwed at 12 in
- Sheets per layer per side: 300 ÷ 32 × 1.1 → 11
- Sheets: 11 × 2 layers × 2 sides = 44 sheets, about 3,098 lb
- Screws: face 35 and base 21 per sheet position; 11 × 2 × 56 = 1,232
- Perimeter: 160 ft
Three thousand pounds of board is a boom-truck delivery. The base and face layers are staggered so no joint lines up through the wall.
Where to find your inputs
Listing. The GA file or UL design number on the drawings, or from the building department. If you have the listing, the custom option lets you enter its details.
Wall size. Floor to the structure above, not to a dropped ceiling, and the full length of the rated wall.
Screw spacing. From the listing, for the face layer.
Sheet size. Rated listings usually allow any length of sheet; some specify orientation, which the preset records.
Common mistakes
- Wider screw spacing. Seven inches means seven inches. Wider voids the rating.
- Regular 5/8 in board. Not type X, not rated.
- Untaped joints in the attic. Tape and cover every joint and head.
- Stopping at the ceiling grid. Run the wall to the deck.
- Penetrations left open. Every pipe, wire and box through a rated wall needs a listed firestop.
- Mixing listings. Take every detail from one listing.
Questions people ask
- What is a fire-rated assembly?
- A wall, floor or ceiling built exactly as one that was tested in a furnace to ASTM E119 and held for the rated time. The listing, in the Gypsum Association's GA-600 manual or the UL directory, specifies the studs, the board type and layers, the fastener type, length and spacing, the joints and any insulation. The rating applies only when every item matches.
- What is in a one-hour wood-stud wall?
- GA-600 file WP 3660, for example, is one layer of 5/8 in type X on each side of 2 × 6 studs at 16 in on centre, applied at right angles to the studs, with 2-1/4 in screws 7 in on centre. Its companion WP 3661 adds 5-1/2 in mineral fibre insulation and spaces the screws 12 in on centre.
- How many screws for a fire-rated wall?
- As many as the listing's spacing gives. At 7 in on centre along each stud, a 4 × 8 sheet hung across 16 in studs takes 49 screws; at 12 in it takes 35. Wider spacing than the listing voids the rating, so the calculator uses the listing's figure.
- Do fire-rated walls need taped joints?
- Yes. Listings require the joints taped and the fastener heads covered, at least a Level 1 finish, even where the wall will never be painted, such as an attic or a garage. Gaps at the perimeter and around penetrations are sealed with a listed firestop sealant.
- What is the difference between this and the fire-rated drywall calculator?
- The fire-rated drywall calculator counts sheets of type X for a rating or a location, quickly. This page works from a specific listing: its screw spacing, its insulation and its layers, and lets you enter the details of your own listing so the materials match it.
- Can I make my own fire-rated wall from type X board?
- No. Type X board is a component; the rating comes from the tested assembly. Using type X in an untested arrangement may be safer than regular board, but it carries no rating an inspector can accept.