Plaster Calculator
Estimate bags of veneer plaster or gypsum basecoat, blueboard or lath, and mixing water for a wall, with coverage for skim coat, basecoat and two-coat plaster.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- 50 lb bags of veneer plaster
- 2 bags
- About 100 sq ft per bag; 198 sq ft including 10% waste
- Wall area
- 180 sq ft
- 20 ft x 9 ft minus openings
- Blueboard sheets
- 7 sheets
- 4 ft x 8 ft, 32 sq ft each, including 10% for cuts
- Mixing water
- 6 gal
- About 3 gal per 50 lb of dry plaster; check the bag and mix small batches
Plaster formula
Wall area = Length x Height - openings; Order area = Wall area x (1 + waste %)
Bags = Order area / coverage per bag (veneer 100 sq ft per 50 lb, basecoat 50 sq ft per 80 lb, two-coat over lath 12 sq ft per 80 lb)
Sheets or lath pieces = Order area / 32 sq ft (blueboard) or / 18 sq ft (lath)
Mixing water (gal) = Bags x bag weight (lb) x 3 / 50Worked example
A 15 x 8 ft wall with one 20 sq ft door, veneer plaster over new blueboard: 15 x 8 - 20 = 100 sq ft, or 110 sq ft with 10% waste. Veneer plaster: 110 / 100 = 1.1, so 2 bags of 50 lb. Blueboard: 110 / 32 = 3.4, so 4 sheets. Water: 2 x 50 x 3 / 50 = 6 gallons.
If the same wall gets a 1/8 in gypsum basecoat first, that is 110 / 50 = 2.2, so 3 bags of 80 lb basecoat and 3 x 80 x 3 / 50 = 14.4 gallons of water, plus the 2 bags of veneer finish on top.
Quick reference
| Wall area | Veneer (50 lb bags) | Basecoat (80 lb bags) | Two-coat over lath (80 lb bags) | Water for veneer |
|---|---|---|---|---|
| 100 sq ft | 2 | 3 | 10 | 6 gal |
| 200 sq ft | 3 | 5 | 19 | 9 gal |
| 300 sq ft | 4 | 7 | 28 | 12 gal |
| 400 sq ft | 5 | 9 | 37 | 15 gal |
| 500 sq ft | 6 | 11 | 46 | 18 gal |
| 800 sq ft | 9 | 18 | 74 | 27 gal |
Veneer plaster vs traditional three-coat
Veneer plaster is the modern system: blueboard goes up like drywall, the joints are taped with fiberglass mesh, and one or two thin coats of plaster are troweled over the whole surface. A room can be boarded, plastered and ready for paint in two or three days, and the result is harder and smoother than taped drywall. It is the right choice for new work and additions.
Traditional three-coat plaster over lath is a scratch coat and brown coat of gypsum or lime basecoat about 1/2 in thick, followed by a finish coat. It uses four to eight times as much material per square foot, takes a week or more of curing, and calls for an experienced plasterer. It is mostly used to match existing walls in older houses and for curved or ornamental work.
Mixing and applying plaster
Add the plaster to clean water, never water to plaster, and mix only what you can apply in the working time on the bag, usually about an hour. A dirty bucket or old plaster in the mixer shortens the set. Keep the blueboard dry before plastering; the board's paper does the bonding, and wet board blisters.
Over painted walls or standard drywall, brush on a plaster bonding agent first or the veneer coat can peel. Apply the first coat tight to the board, then double back with a second coat to fill and smooth, and trowel it to the finish you want as it firms up. Keep leftover dry plaster sealed; an open bag absorbs moisture and sets faster.
Key facts
- Veneer plaster is applied only 1/16 to 3/32 in thick over blueboard, a gypsum board with an absorbent face paper made for plaster.
- A 50 lb bag of veneer finish plaster covers about 100 sq ft; an 80 lb bag of gypsum basecoat covers about 50 sq ft at 1/8 in.
- Traditional plaster over metal lath is about 5/8 in thick: a 1/2 in scratch and brown basecoat plus a 1/16 to 1/8 in finish.
- Veneer plaster sets in about an hour or two and can usually be painted after a day or two; joint compound needs a full day to dry per coat.
- Blueboard comes in the same 4 x 8 ft sheets and 1/2 and 5/8 in thicknesses as drywall and is hung with the same screws.
Frequently asked questions
How much does a bag of veneer plaster cover?
About 100 sq ft per 50 lb bag at 1/16 to 3/32 in. A 12 x 12 ft room with 8 ft ceilings has about 334 sq ft of wall after openings, which needs 4 bags with 10% waste.
Can I put veneer plaster over regular drywall?
Not directly. Standard drywall paper is not absorbent enough and the plaster can peel. Use blueboard for new work, or brush a plaster bonding agent over existing drywall or painted walls first.
How much water do I mix with plaster?
About 3 gallons (12 quarts) per 50 lb bag of veneer plaster, so 2 bags take about 6 gallons. Follow the ratio on the bag and add the plaster to the water, not the other way around.
How thick is plaster?
Veneer plaster is 1/16 to 3/32 in over blueboard. A gypsum basecoat adds about 1/8 in under a veneer finish. Traditional plaster over metal lath is about 5/8 in in total.
Sources and references
Next steps for this project
The usual order for a paint & walls project. See all paint & walls calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.