Gypsum Plaster Scratch Coat Volume Calculator

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Wall/Ceiling Area

The total area to receive the scratch coat.

Measure the actual lath or substrate area that will be plastered.

Scratch Coat Thickness

The applied thickness of the scratch coat.

The scratch coat is typically the thickest of the three plaster coats, commonly around 10 mm, since it fills and keys into the lath.

Scratch coat plaster volume

77.8 gal

High confidence

Equivalent volume: 0.39 yd³

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

Three-coat plaster system volume per coat = wall area × coat thickness; the scratch coat is typically the thickest of the three coats (commonly ~10 mm)

Inputs used

Wall/Ceiling Area: 320 sq ft
Scratch Coat Thickness: 0.39 in

Intermediate steps

Equivalent volume: 0.39 yd³

Final result77.8 gal

What this calculation does not cover

Gives the volume on the wall, and plaster is bought in bags. Turning one into the other needs the product's yield: gypsum basecoat is mixed with sand at a ratio the manufacturer sets, commonly somewhere around 2:1 to 3:1 by volume for a scratch coat, and one bag of neat plaster covers a very different area depending on which ratio is used and how the sand is graded. Read the yield off the bag and divide - a bare volume cannot be ordered.
Says nothing about how much never reaches the wall. Hand-applied basecoat is lost off the hawk, off the trowel, onto the boards, and in whatever is left in the bath when the mix goes off - and gypsum basecoat sets on a clock that cannot be extended, so any batch mixed larger than the plasterer can hang inside that window is thrown away. Batch to the working time rather than to the total, and expect the practical figure for droppings and part-batches to sit well above the clean number this sum returns.
One coat out of a system that is specified as a total. Interior gypsum plaster over metal lath is normally required to reach a nominal total thickness, commonly quoted at 5/8 in (16 mm) measured from the face of the lath across scratch, brown and finish - and where the wall or ceiling carries a fire rating, that full thickness and that lath are part of what was tested. Trimming the scratch coat here only pushes material into the brown coat; taking it out of the total is a different assembly.

Estimated cost — your price

Price per gal ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations1

Three-coat plaster system volume per coat = wall area × coat thickness; the scratch coat is typically the thickest of the three coats (commonly ~10 mm)

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To skim a plaster finish. Generic types, no brands, no prices.

Protection this work requires

Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
Most fatal falls on small jobs are from under three metres: use a tower or a ladder tied at the top, and never work off the top two rungs.

Show the 4 tools this job needs

Essential

Mixing bucket or tub
Paddle mixer
Plastering trowel and hawk

Recommended

Step ladder

what each plastering tool is for, and the spec that decides which to buy where one does.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Injecting a Remedial DPC and Replastering After Ituses this calculator

Hole spacing, cream volume per metre, what the drying wait is really for, and why the replaster over an injected course is a salt specification.

Rendering and Plastering a Walluses this calculator

A coat-by-coat field guide to render and plaster: reading what the background drinks, and keeping every coat weaker and thinner than the one beneath it.

Plastering Over Artex

Wall/Ceiling Area	Scratch coat plaster volume (gal)
200 sq ft	49.1
300 sq ft	73.6
400 sq ft	98.2
500 sq ft	123
600 sq ft	147

Wall/Ceiling Area

Scratch coat plaster volume (gal)

200 sq ft

49.1

300 sq ft

73.6

400 sq ft

98.2

500 sq ft

123

600 sq ft

147

Frequently asked questions

Why is the scratch coat thinner than the coat above it?

Because its job is grip, not flatness. The scratch coat is pressed into the background or through the lath and then deliberately raked across while green, so the next coat has a key to hold onto — a smooth first coat is the classic reason a three-coat system later parts company with the wall. It follows the background rather than correcting it, which is why its quantity barely moves when the wall is out of true: the material that fills hollows and brings the face to a plane belongs to the brown coat, and adding it here just gives you a thick coat that shrinks and cracks while the plane is still wrong.

Why is the scratch coat the thickest of the three coats?

The scratch coat has to fill the keys of the lath and establish a solid base for the coats that follow, which typically makes it the thickest layer in a three-coat plaster system, commonly around 10 mm.

How is plaster volume converted to liters?

Volume in cubic meters is multiplied by 1,000 to convert to liters (1 m³ = 1,000 L), since plaster and other wet mixes are commonly quoted and mixed by liter or gallon rather than cubic meter.

Does this account for lath keying or texture that increases material use?

No — this is a straight area × thickness volume calculation. Rough or heavily keyed lath, and any hand-applied texture beyond a flat coat thickness, will use more material than this base volume.