Calculate how many 1200 × 2400 mm (4 × 8 ft) or 1200 × 3600 mm drywall sheets you need, plus joint compound tubs, tape rolls, and screw counts — based on room perimeter, ceiling height, and an optional ceiling.
What Your Results Mean
Measure the longest wall first — that's your room length. Then measure the perpendicular wall for width. For ceiling height, measure from the finished floor to the finished ceiling; 2.7 m (9 ft) is the most common modern ceiling height, 2.4 m (8 ft) is standard in older homes, and 3.0–3.6 m (10–12 ft) appears in newer construction with vaulted or raised ceilings. If your ceiling is sloped or vaulted, use the average height for the wall measurement and toggle the ceiling checkbox off (you'll need to estimate the vault separately).
Sheet size choice depends on three things: ceiling height, available labor, and access. 1200 × 2400 mm sheets (2.88 m² each, the classic 4 × 8 ft) are the residential default because one person can hang them. 1200 × 3600 mm sheets (4.32 m² each) cover 50% more area per sheet, which means fewer joints to tape and mud — but they weigh over 33 kg and require a drywall lift or two strong installers. For rooms with narrow stair access, stick with 1200 × 2400 mm sheets even if the math favors the longer ones.
The "include ceiling" checkbox adds the room's footprint area (length × width) to the wall area total. Leave it unchecked if your ceiling is already finished, exposed beam, or if you're only hanging walls. The estimator assumes one continuous room; for L-shaped or open-concept spaces, treat each rectangle separately and add the results.
What's in the Results
- Total Area: Sum of wall area (perimeter × height) plus ceiling area if included. This is the surface area your sheets must cover.
- Sheets Needed: Total area ÷ sheet area (2.88 or 4.32 m²), rounded up. Includes a small scrap allowance embedded in the rounding.
- Screws: Industry standard of 32 screws per 1200 × 2400 mm sheet or 48 per 1200 × 3600 mm sheet — one screw every 300 mm (12 in) on studs and around the perimeter.
- Joint Compound: One 17 L (4.5-gal, about 21 kg) tub covers approximately 37 m² (400 sq ft) of board for a three-coat finish (tape coat, fill coat, skim coat).
- Tape: One 76 m (250 ft) roll of paper tape covers approximately 76 m of joints. The estimator calculates total joint length based on sheet count and standard perimeter.
Pro Tip
Buy 10% more compound than the calculator shows. Running out mid-finish means a trip to the supplier with wet tools, and leftover compound stores for months if sealed airtight.
The Math Behind the Calculator
Drywall estimating starts with surface area and works backward to material counts. The fundamental equation:
wall_area = (2 × (length + width)) × height
ceiling_area = length × width (if included)
total_area = wall_area + ceiling_area
sheets_needed = ceil(total_area / sheet_area)
For 1200 × 2400 mm sheets, sheet_area = 2.88 m². For 1200 × 3600 mm sheets, sheet_area = 4.32 m². The ceiling function rounds up because you can't buy a fractional sheet.
Screw Count
US building code (IRC R702.3.5) requires drywall fasteners every 300 mm (12 in) in the field and every 200 mm (8 in) on the perimeter for ceiling applications, and every 300 mm (12 in) for walls. The practical rule of thumb used by installers is 32 screws per 1200 × 2400 mm sheet and 48 per 1200 × 3600 mm sheet, which gives a small safety margin over the strict code minimum.
Joint Compound Coverage
A 17-litre (4.5-gallon) tub of all-purpose joint compound weighs about 21 kg and covers approximately 37 m² (400 sq ft) of board for a complete three-coat tape-and-finish process. Lightweight formulations cover slightly less (about 32 m²) but are easier to sand. Setting-type compounds (the kind you mix from powder) cover similarly but cure chemically in 20 to 90 minutes rather than drying by evaporation.
Tape Length Estimation
Tape runs along every joint between sheets. For a typical installation, the joint length equals roughly 75% of the total sheet perimeter length (the other 25% is the perimeter where sheets meet walls and don't need tape). The formula used:
joint_length = sheets × (sheet_width + sheet_height) × 0.75
// one roll = 76.2 m (250 ft) of tape
tape_rolls = ceil(joint_length / 76.2)
Assumptions & Limitations
Every number above rests on these constants. If your project differs, change the matching input — or read the linked guide for the full reasoning.
- Area is wall area (minus openings at 1.9 m² per door, 1.4 m² per window)
- Sheets are counted whole — always rounded up
- Screws: 32 per 1200 × 2400 mm sheet (48 per 1200 × 3600 mm), per industry fastening practice
- Compound baseline: one 17 L (21 kg) tub per 37 m² (400 sq ft) at Level 4 finish
Worked Example: 5 × 4 m Bedroom with 2.7 m Ceilings
Consider a master bedroom 5 metres by 4 metres with 2.7 m (9 ft) ceilings, drywall on walls and ceiling, using standard 1200 × 2400 mm sheets. Here's how the math plays out:
- Wall area: perimeter = 2×(5+4) = 18 m. Wall area = 18 × 2.7 = 48.6 m².
- Ceiling area: 5 × 4 = 20 m².
- Total area: 48.6 + 20 = 68.6 m².
- Sheets: 68.6 ÷ 2.88 = 23.8 → 24 sheets of 1200 × 2400 mm.
- Screws: 24 × 32 = 768 screws (1 box of 1000 with margin).
- Joint compound: 68.6 ÷ 37 = 1.85 → 2 tubs (17 L, about 21 kg each).
- Tape: 24 × (1.2+2.4) × 0.75 = 64.8 m → 1 roll (76 m covers it).
- Order summary: 24 sheets of 1200 × 2400 mm board, one 1,000-count box of screws, 2 tubs of compound and 1 roll of tape — the full hanging kit for this room.
If you switched to 1200 × 3600 mm sheets on the same room, you'd need 16 sheets instead of 24 (68.6 ÷ 4.32 = 15.9, rounded up). That saves 8 sheets of handling, 8 joints to tape, and roughly an hour of hanging labour — but the longer sheets are harder for one person to handle alone and may need a second installer or a panel lift. For a single bedroom the switch rarely makes sense; for a whole-house build it usually does.
Reminder
The estimate excludes corner bead, sanding sponges, masks, drop cloths, primer and paint. Treat it as a board-and-consumables checklist, and add for corners and finishes before you shop.
