How much wastage should I allow?

Wastage covers cuts, breakages and the offcut at the end of every run. Ordering the exact computed quantity reliably means a second trip.

Construction & HomefinishingUnited States only

Drywall Calculator

Plasterboard sheets from wall or ceiling area. A standard 8 by 4 foot sheet covers about 2.97 square metres, and ten percent wastage is normal for a straightforward room.

Also called: plasterboard calculator, gypsum board quantity.

Sheets

7.64

7.64 sheets for 20 m² over 1 coat(s), including 10% wastage.

Area after deductions (m²)

Area across all coats (m²)

Before wastage

6.94

Area one unit covers (m²)

2.88

How this is calculated

Method and background

How this is calculated

Area divided by sheet coverage, plus wastage. Ceilings waste more than walls because the cuts around light fittings and the awkwardness of holding a sheet overhead both produce breakages. Fixing on both sides of a partition doubles the sheet count, which the coat multiplier handles.

quantity = area * coats / coverage per unit, plus wastage

A: Net area (m2)
c: Coats (count)
r: Coverage per unit (m2)
s: Wastage (decimal)

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

a partition boarded one side

Length (m): 8
Width or height (m): 2.7
Or enter the area directly (m²): 0
Openings to deduct (m²): 0
Area one sheet covers (m²): 2.97
Coats or layers: 1
Wastage: 10%

Sheets8

21.6 / 2.97, worked by hand

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boarding both sides doubles it

Length (m): 8
Width or height (m): 2.7
Or enter the area directly (m²): 0
Openings to deduct (m²): 0
Area one sheet covers (m²): 2.97
Coats or layers: 2
Wastage: 10%

Sheets16

boundary

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no area needs no board

Length (m): 0
Width or height (m): 0
Or enter the area directly (m²): 0
Openings to deduct (m²): 0
Area one sheet covers (m²): 2.97
Coats or layers: 1
Wastage: 10%

Sheets0

degenerate case

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Method and limits

What it assumes

One layer per surface unless the coat count is raised.

What it deliberately does not model

Fixings, joint compound and tape are separate quantities and are not included.
Fire-rated or acoustic construction often needs two layers, which changes the count and the fixings.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

How much wastage should I allow?: Wastage covers cuts, breakages and the offcut at the end of every run. Ordering the exact computed quantity reliably means a second trip.