Stucco and Plaster Bag Calculator
Project inputs
Start with the essentials. Every preset is editable; use the exact coverage on your bag or technical data sheet before ordering.
Advanced options: precision, cost, extra bags, and accessories
Planning quantities only. Confirm laps, layer count, spacing, fasteners, and code requirements from the selected wall assembly.
Shopping list
Enter the project and product details to see the estimate.
| Material / method | Exact | Purchase | Package | Waste | Mixing water | Subtotal |
|---|
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Worked examples
Example 1: three-coat exterior stucco wall with openings
Inputs: one 20 ft × 10 ft wall; one 3 ft × 7 ft door; two 3 ft × 4 ft windows; 10% waste. Scratch and brown coverage is 26.6 sq ft per 80 lb bag at 3/8 in; finish coverage is 70 sq ft per 80 lb bag at 1/8 in.
Area: gross = 20 × 10 = 200 sq ft. Openings = (3 × 7) + 2 × (3 × 4) = 45 sq ft. Net = 200 − 45 = 155 sq ft.
Scratch: 155 × 1.10 ÷ 26.56 = 6.42 bags → order 7. Brown: the same substitution gives 6.42 → order 7. Finish: 155 × 1.10 ÷ 70 = 2.44 → order 3. Final order: 17 bags. The waste-adjusted exact quantities are shown before each product is rounded.
Example 2: metric room skim plaster, walls and ceiling
Inputs: 4 m × 3 m room, 2.4 m high; walls and ceiling; 0.9 m × 2.1 m door; 1.2 m × 1.2 m window; 25 kg plaster covering 10 m² at 2 mm; 10% waste; 11.5 L mixing water per bag.
Area: walls = 2 × (4 + 3) × 2.4 = 33.60 m²; ceiling = 4 × 3 = 12.00 m²; openings = 1.89 + 1.44 = 3.33 m²; net = 45.60 − 3.33 = 42.27 m².
Bags: 42.27 × 1.10 ÷ 10 = 4.65 exact → order 5 bags. Mixing water = 5 × 11.5 = 57.5 L. Water is a planning total; follow the bag’s mixing instructions and do not automatically add the full amount at once.
Quick answers for 100 sq ft and 10 m²
Planning examples include the preset waste and round each product separately. Your label value can change the answer.
| System | Planning inputs | 100 sq ft | 10 m² |
|---|---|---|---|
| Three-coat stucco | Scratch 26.6, brown 26.6, finish 70 sq ft/bag; 10% | 12 bags total (5 + 5 + 2) | 12 bags total (5 + 5 + 2) |
| One-coat stucco | 22 sq ft/80 lb bag at 3/8 in; 10% | 5 bags | 5 bags |
| Finish skim | 10 m²/25 kg bag at 2 mm; 8% | 2 bags | 2 bags |
| One-coat render | 1 m²/25 kg bag at 15 mm; 10% | 11 bags | 11 bags |
Coverage and thickness planning examples
These are examples, not universal specifications. Select the closest preset to explore the calculator, then replace every value with the package label, technical data sheet, approved assembly, and project specification.
| Application | Typical planning thickness | Example package and coverage | Common use and source |
|---|---|---|---|
| Three-coat stucco: scratch | 3/8 in (9.5 mm) | 80 lb; 0.83 cu ft wet yield ≈ 26.6 sq ft | Base/key coat. QUIKRETE Base Coat data sheet |
| Three-coat stucco: brown | 3/8 in (9.5 mm) | 80 lb; 0.83 cu ft wet yield ≈ 26.6 sq ft | Leveling/base coat. QUIKRETE stucco calculator |
| Stucco finish | 1/8 in (3.2 mm) | 80 lb; about 70 sq ft | Decorative finish. QUIKRETE Finish Coat data sheet |
| Proprietary one-coat stucco | 3/8 in (9.5 mm) | 80 lb; about 20–24 sq ft | Evaluated one-coat assembly. QUIKRETE One Coat FRS data sheet |
| Skim / finish plaster | 2 mm total in two passes | 25 kg; about 10 m²; 11.5 L water | Interior finish. British Gypsum MultiFinish data sheet |
| Bonding / base plaster | 11 mm walls; 8 mm plasterboard or ceilings | 25 kg; enter label coverage; about 14 L water | Low-suction base coat. British Gypsum BondingCoat instructions |
| One-coat render | 15 mm finished | 25 kg; about 1 m² per bag | Through-coloured render. Weber weberpral E data sheet |
Methodology and formulas
Page updated: 15 July 2026. Preset revision: 15 July 2026. Formulas and implementation are maintained by Starlight Tools; no external reviewer is claimed.
- Gross single-wall area:
width × height × repeated wall count - Gross room wall area:
2 × (length + width) × height; ceiling =length × width - Net area:
gross area − quick opening total − individual openings - Coverage method: coverage is scaled inversely when entered coat thickness differs from the label thickness; bags =
net area × (1 + waste%) ÷ adjusted coverage - Wet-volume method: bags =
net area × coat thickness × (1 + waste%) ÷ wet yield per bag - Dry-consumption method: kg =
net m² × kg/m²/10 mm × thickness mm × (1 + waste%); bags =kg ÷ bag kg - Total-weight method: bags =
entered total dry kg × (1 + waste%) ÷ bag kg - Purchase quantity: each active coat is rounded up separately; optional extra packages are added after coat rounding.
Coverage varies with substrate suction, surface plane, texture, aggregate, mixing, application method, and loss. Proprietary one-coat systems and EIFS are assemblies: use their current manufacturer evaluation report and component specifications, not a generic thickness. This calculator does not design a wall assembly or determine code compliance.
Sources
- ASTM C926, Standard Specification for Application of Portland Cement-Based Plaster — scope and system thickness tables.
- QUIKRETE Base Coat Stucco – Pump Grade data sheet — 80 lb package, 0.83 cu ft yield, water guidance, scratch/brown use.
- QUIKRETE Finish Coat Stucco data sheet — 80 lb package, 70 sq ft at 1/8 in, 0.75 cu ft yield.
- British Gypsum Thistle MultiFinish data sheet — 25 kg, 10 m² at 2 mm, 11.5 L water.
- Weber weberpral E data sheet — 25 kg, 1 m² at 15 mm planning example.
How to calculate stucco or plaster bags
- Choose the material mode and units: Choose exterior stucco, interior plaster or skim, or render, then select imperial or metric units.
- Measure the coated surfaces: Enter a single wall, room perimeter, repeatable walls, or a known area; include the ceiling only when it will be coated.
- Subtract openings: Add individual doors and windows or enter an existing total opening takeoff, without counting the same opening twice.
- Enter each product label: For each active coat, enter its thickness and choose coverage, wet yield, dry consumption, or total material weight from the product label.
- Order whole packages: Apply waste to each coat, divide by its package yield, and round each coat up to a whole bag or pail.
Stucco and plaster questions
How many 80 lb stucco bags cover 100 sq ft?
Using the planning examples, 100 sq ft before waste needs about 3.77 bags for each 3/8 in scratch or brown coat at 26.6 sq ft per 80 lb bag, or 1.43 bags for a 1/8 in finish at 70 sq ft per bag. Add the selected waste and round each product up separately.
How many 25 kg plaster bags cover 10 m²?
A product labelled 10 m² per 25 kg bag at 2 mm needs exactly one bag for 10 m² before waste. With 10% waste the calculator shows 1.10 exact bags and a two-bag purchase quantity.
What is a typical thickness for each stucco or plaster coat?
Planning examples on this page use 3/8 in scratch, 3/8 in brown, 1/8 in stucco finish, 3/8 in one-coat stucco, 11 mm bonding plaster, 2 mm skim plaster, and 10 mm render. Replace these with the project specification or product data sheet.
What waste percentage should I use?
Use about 5% to 10% for measured flat work and more for rough or porous walls, deep texture, many corners, small batches, pump loss, or repairs. Waste is applied to every active coat before rounding.
Should I subtract small doors, windows, and openings?
Subtract meaningful uncoated areas. Leaving very small openings in the gross area can provide a practical cutting and handling allowance, but do not also count that allowance as waste.
How are ceilings measured for plaster?
Ceiling area is room length multiplied by room width. In room-perimeter mode choose ceilings or walls and ceilings; openings are deducted from the combined selected area.
Where do I find label consumption or coverage?
Check the coverage, yield, consumption, or technical data section on the bag and product data sheet. Enter both the stated coverage and its stated thickness, or choose the matching yield method.
Why might actual use be higher on uneven or porous walls?
Low spots increase average thickness, while porous backgrounds can shorten working time and increase tool or mixing loss. Measure average depth carefully and increase the calculator waste input when conditions justify it.