Should I hang drywall vertically or horizontally on walls?

In Australia and most of the world, plasterboard is hung vertically (long edge vertical, parallel to studs) as the preferred method for residential walls. This minimises horizontal butt joints and works well for standard ceiling heights. In the US, horizontal hanging (long edge horizontal, perpendicular to studs) is common in residential construction because it produces stronger walls (the board crosses more studs) and reduces the number of butt joints when sheets are long enough to span full wall widths. Follow the manufacturer's installation guide for the specific product and application.

What is the difference between standard and moisture-resistant plasterboard?

Standard plasterboard (Gyprock Standard, USG Sheetrock) has a paper facing on a gypsum core and is suitable for dry interior areas. Moisture-resistant (MR) plasterboard has a treated core and moisture-resistant facing suitable for areas with intermittent moisture exposure (bathroom walls away from the shower, laundries). Water-resistant (WR) or tile backer products use a fibrous or cement-based core for areas of direct water contact. Wet areas (inside shower recesses) should use fibre cement board or a proprietary shower backer system rated for direct water contact.

How do I calculate drywall for a room with a vaulted or raked ceiling?

For raked ceilings, calculate the actual ceiling area using the sloped dimension (not the plan view area). For a room with a ceiling that rises from 2.4m to 3.6m over a 5m run: the slope length is sqrt(5^2 + 1.2^2) = 5.14m. Multiply by the room width for the ceiling area. Use 18-25% waste for raked ceilings because the angle means fewer sheets fit a standard panel layout without significant cuts.

Drywall / Plasterboard Calculator — Free Construction Calculator

🎯

A plasterer is lining a new extension -- 85 m2 of walls and 32 m2 of ceiling. Before the materials order goes in, they need the sheet count and confirm whether 10% waste is enough for a straightforward rectangular room.

Drywall / Plasterboard Calculator

Lining

Total wall area (m²)

Measure all walls, subtract door/window openings

Ceiling area (m²)

Sheet size

Waste factor (%)

10% standard, 15% for complex rooms

AU (plasterboard): Standard 1200×2400mm, 10mm walls, 13mm ceilings. Also 1200×3000mm for 2.7m ceilings (fewer joints). Fire-rated, moisture-resistant and acoustic sheets available.
US (drywall): Standard 4×8ft (most common), 4×12ft reduces joints. ½" (12.7mm) walls, ⅝" (15.9mm) fire-rated and ceilings.
For ceilings, standing seam direction matters — always run sheets perpendicular to joists.

Reference: Gyprock — Technical Guide

ℹ️ Results are estimates for planning purposes. Verify with current standards and a qualified professional.

1 What this calculator does

Calculates the number of plasterboard or drywall sheets needed for walls and ceiling from total areas, sheet size and waste percentage. Supports AU sheet sizes (1200x2400mm, 1200x3000mm) and US sheet sizes (4x8ft, 4x12ft). Shows sheets for walls and ceiling separately.

2 Formula & professional reasoning

Total area = Wall area + Ceiling area
Area with waste = Total area x (1 + Waste%/100)
Sheets = Ceiling(Area with waste / Sheet area m2)
Sheet areas: AU 1200x2400mm = 2.88 m2 | AU 1200x3000mm = 3.60 m2
  US 4x8ft = 2.98 m2 | US 4x12ft = 4.46 m2

Sheet count is the total area to be covered including waste, divided by the area of one sheet, rounded up to a whole number (ceiling function). Walls and ceiling are calculated separately because they often use different sheet sizes (longer sheets on walls to minimise horizontal joints) and different waste allowances (ceilings often have more waste due to the need for continuous long runs). The standard 10% waste allowance accounts for cuts at corners, around doors and windows, and the odd damaged sheet.

3 Worked examples

⚠️ Illustrative example only — not clinical or professional instruction.

Basic

Standard room lining -- walls and ceiling

Given: Wall area: 85 m2 | Ceiling area: 32 m2 | Sheet: AU 1200x2400mm (2.88 m2) | Waste: 10%

Working: Total: 85 + 32 = 117 m2 | With waste: 117 x 1.10 = 128.7 m2 | Sheets: ceiling(128.7/2.88) = ceiling(44.7) = 45 sheets

Answer: 45 sheets of 1200x2400mm plasterboard

💡 For a better result use different sheet sizes: 1200x3000mm for walls (fewer joints) and 1200x2400mm for ceiling. Walls: ceiling(85x1.10/3.60) = 27 sheets x 3000mm. Ceiling: ceiling(32x1.10/2.88) = 13 sheets x 2400mm. Total 40 sheets but two different sizes.

Standard

US drywall estimate -- 4x8 sheets

Given: Wall area: 920 sq ft | Ceiling area: 340 sq ft | Sheet: US 4x8ft (2.98 m2 = 32 sq ft) | Waste: 12%

Working:

Total: 920 + 340 = 1,260 sq ft | With 12% waste: 1,260 x 1.12 = 1,411 sq ft | Sheets: ceiling(1411/32) = ceiling(44.1) = 45 sheets

Answer: 45 sheets of 4x8ft drywall

💡 For walls in tall rooms (9-10ft ceiling), use 4x10ft or 4x12ft sheets to avoid horizontal butt joints. 4x12ft covers 48 sq ft: ceiling(920x1.12/48) = ceiling(21.5) = 22 sheets. More cost per sheet but fewer joints and less tape/compound.

Advanced

Commercial fit-out with high waste for complex ceilings

Given: Wall area: 640 m2 | Ceiling area: 280 m2 | Sheet: AU 1200x3000mm (3.60 m2) | Wall waste 10% | Ceiling waste 18% (coffered, complex)

Working:

Walls: ceiling(640 x 1.10 / 3.60) = ceiling(195.6) = 196 sheets | Ceiling: ceiling(280 x 1.18 / 3.60) = ceiling(91.8) = 92 sheets | Total: 288 sheets

Answer: 196 sheets walls + 92 sheets ceiling = 288 sheets total

💡 Complex coffered or bulkhead ceilings generate significantly more waste than flat ceilings. Use 15-20% waste for coffered ceilings and 10% for flat ceilings. Always estimate walls and ceiling separately when waste factors differ.

4 Sanity check

Standard sheet sizes and coverage

AU 1200x2400mm: 2.88 m2 | AU 1200x3000mm: 3.60 m2 | US 4x8ft: 2.98 m2 (32 sq ft) | US 4x10ft: 3.72 m2 | US 4x12ft: 4.46 m2

Waste allowance by application

Simple rectangular rooms: 10% | Rooms with many windows and doors: 12-15% | Complex ceiling shapes: 15-20% | Angled ceilings or raked walls: 18-25%

Sheet orientation for walls

Hang sheets vertically (long edge vertical) to minimise horizontal butt joints | Use the longest sheet that fits the wall height without a horizontal join

A 2.7m ceiling wall uses 1200x2700mm or 1200x3000mm sheets (overlapping at the floor) -- no horizontal join.

Ceiling sheets

Hang ceiling sheets perpendicular to joists | Stagger end joints between rows | Use the longest sheet the room and ceiling space allow to minimise butt joints

5 Common errors

Error	Cause	Consequence	Fix
Not deducting door and window openings from gross wall area	Using the gross perimeter x height without subtracting openings	Overordering sheets by 10-20% in rooms with many windows and doors	Subtract the area of each door (typically 1.8 m2 or 20 sq ft) and each window from the gross wall area. For rooms with a high proportion of glazing (feature walls, bifold doors), deductions can significantly reduce the sheet count.
Using the same sheet size for walls and ceilings without considering room height	Ordering all 2400mm sheets regardless of ceiling height	Walls with horizontal butt joints at mid-height -- more taping, finishing and visible joint lines	Match sheet length to ceiling height. For 2.7m ceilings, 3000mm sheets (trimmed to 2700mm) eliminate horizontal joints on walls. For 3.0m ceilings, 3000mm sheets used full-length are ideal.
Not accounting for fire-rated plasterboard requirements	Specifying standard 10mm plasterboard in a fire-rated wall or ceiling	Non-compliant fire separation -- fails inspection, must be replaced	Fire-rated assemblies (typically walls between garages and living areas, apartment party walls, and commercial fire partitions) require specific fire-rated plasterboard (13mm or 16mm) in specified layer configurations. Check NCC (AU) or IBC (US) requirements and the system manufacturer's test report.
Not specifying moisture-resistant plasterboard for wet areas	Using standard plasterboard behind tiles in wet areas	Plasterboard absorbs moisture through the tile joint, swells and debonds -- tile failure and structural damage	Use moisture-resistant (MR) or water-resistant (WR) plasterboard (e.g. Gyprock Aquachek, USG Durock) as the substrate in all wet areas including showers, bathrooms and laundries. In shower recess areas, a proprietary tile backer board or fibre cement sheet is preferred by many tilers.