Can the finish coat fix an uneven wall?

No, and trying is how finishes fail. It is a few millimetres thick and is applied to a consistent thickness across the surface, so it follows every deviation underneath it rather than filling it. Building it up locally to correct a hollow gives a patch of different thickness that dries at a different rate and shows as a shadow in raking light. Flatness is the brown coat's job.

Why does the finish crack in a fine network?

Usually because it was applied over a background that was still moving — a brown coat that had not cured, or one that was too dry and sucked the water out of the finish before it could set. Both produce crazing across the face. Controlling suction, by dampening or by a bonding treatment, is as important as the mix itself.

Does texture change how much I need?

Yes, and by more than people expect. A tight trowelled finish uses less than a floated or scraped texture, and a heavily textured finish more again, because the material has to fill a deeper profile. Manufacturers publish coverage per texture for this reason, and estimating from a smooth-finish figure understates a textured job.

When can a new finish coat be painted, and with what?

Only once it has dried right through, which on fresh gypsum shows as an even pale colour with no darker patches left; that takes days rather than hours, and longer on a cold or thickly plastered wall. The first coat is either the wall paint thinned with water, a mist coat, or a primer sold for new plaster, because the new surface is so absorbent that paint applied at full strength skins on the face and later peels. Vinyl or other low-permeability finishes go on after that first coat, not as it, so the wall can go on drying through the decoration.

Materials & Quantities

Gypsum Plaster Finish Coat Volume Calculator

Calculate the plaster volume needed for the thin finish coat, the final layer of a three-coat plaster system.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Wall/Ceiling Area

The total area to receive the finish coat.

Use the same area as the brown coat beneath it — the finish coat is applied over the full browned-out surface.

Finish Coat Thickness

The applied thickness of the finish coat.

The finish coat is the thinnest, smoothest layer in a three-coat system, typically applied around 3 mm thick to produce the final surface texture.

Finish coat plaster volume

23.56 gal

High confidence

The finish coat is thin, and its quantity is small relative to the coats beneath. What it is not is forgiving — it reveals whatever the brown coat left behind rather than correcting it.

Equivalent volume: 0.12 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 finish coat is the thinnest, smoothest layer (commonly ~3 mm)

Inputs used

Wall/Ceiling Area: 320 sq ft
Finish Coat Thickness: 0.12 in

Intermediate steps

Equivalent volume: 0.12 yd³

Final result23.56 gal

Confidence note: The finish coat is thin, and its quantity is small relative to the coats beneath. What it is not is forgiving — it reveals whatever the brown coat left behind rather than correcting it.

What this calculation does not cover

A FINISH COAT IS A THICKNESS OF 2-3 MM AND A QUESTION OF FLATNESS, not a quantity to be stretched. Applying it thicker to bury a background that was never levelled is the commonest cause of a finish that crazes or delaminates, and no material figure prevents it.
Set is time, not quantity. A bag mixed and not used inside its working time is waste regardless of the area it would have covered, so the order is governed by how much can be laid in one working period as much as by the wall.
Says nothing about the background it is going on to. Finish plaster over new board, over a brown coat and over painted plaster are three different preparations with three different suction conditions.
Excludes the scratch and brown coats, which together account for most of a rendered wall's material.
Coverage varies markedly with the texture being achieved; a smooth trowelled finish and a heavy float finish consume different amounts of the same product.
Does not include the first coat new plaster takes before it is decorated, a mist coat or a primer made for new plaster, nor the paint that goes over it.

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.

Part of a bigger job

Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.

Room planner

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 2026-08-26 · in the site-wide review of 2026-09-06 · v1.0.0

Regulatory standards & verification citations1

Three-coat plaster system volume per coat = wall area × coat thickness; the finish coat is the thinnest, smoothest layer (commonly ~3 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.
Overboarding or Taking Down a Lath and Plaster Ceilinguses this calculator
Two answers to a bowing Victorian ceiling — board over it or take it out — and the screw length, dust and container size that decide which.
Plastering Over Artexuses this calculator
A textured ceiling takes a skim, an undercoat or a new sheet of board depending on one lab result and one depth gauge reading — not on the primer.

Called something else where you work? Skim coat / joint compound — the term in each market, how close the equivalence really is, and the standard that governs it.

Already gone wrong? The paint is peeling off my new plaster · My paint is blistering or bubbling · My plaster sounds hollow, or has blown off the wall

The data behind it: Production rates by operation

How to calculate gypsum plaster finish coat volume in 3 steps

Wall/Ceiling AreaThe total area to receive the finish coat.
Finish Coat ThicknessThe applied thickness of the finish coat.
Finish coat plaster volumeThe tool computes the finish coat plaster volume from those figures and shows the formula, its sources, and a confidence rating alongside it.

Finish coat plaster volume by wall/ceiling area

Page defaults, not your figures above.

Wall/Ceiling Area	Finish coat plaster volume (gal)
200 sq ft	14.7
300 sq ft	22.1
400 sq ft	29.5
500 sq ft	36.8
600 sq ft	44.2

Frequently asked questions

Can the finish coat fix an uneven wall?: No, and trying is how finishes fail. It is a few millimetres thick and is applied to a consistent thickness across the surface, so it follows every deviation underneath it rather than filling it. Building it up locally to correct a hollow gives a patch of different thickness that dries at a different rate and shows as a shadow in raking light. Flatness is the brown coat's job.
Why does the finish crack in a fine network?: Usually because it was applied over a background that was still moving — a brown coat that had not cured, or one that was too dry and sucked the water out of the finish before it could set. Both produce crazing across the face. Controlling suction, by dampening or by a bonding treatment, is as important as the mix itself.
Does texture change how much I need?: Yes, and by more than people expect. A tight trowelled finish uses less than a floated or scraped texture, and a heavily textured finish more again, because the material has to fill a deeper profile. Manufacturers publish coverage per texture for this reason, and estimating from a smooth-finish figure understates a textured job.
When can a new finish coat be painted, and with what?: Only once it has dried right through, which on fresh gypsum shows as an even pale colour with no darker patches left; that takes days rather than hours, and longer on a cold or thickly plastered wall. The first coat is either the wall paint thinned with water, a mist coat, or a primer sold for new plaster, because the new surface is so absorbent that paint applied at full strength skins on the face and later peels. Vinyl or other low-permeability finishes go on after that first coat, not as it, so the wall can go on drying through the decoration.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.