Enter wall or room measurements, subtract openings, select a stucco, plaster, skim, or render system, and get whole bags by coat with optional water and cost.
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
Added to the overall order, not every coat.
Planning quantities only. Confirm laps, layer count, spacing, fasteners, and code requirements from the selected wall assembly.
Enter the project and product details to see the estimate.
Gross area—
Opening deduction—
Net coated area—
Total estimated cost—
Material / method
Exact
Purchase
Package
Waste
Mixing water
Subtotal
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.
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.
Page updated: 15 July 2026. Preset revision: 15 July 2026. Formulas and implementation are maintained by Starlight Tools; no external reviewer is claimed.
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.
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.
