Plaster Calculator

About Plaster Calculation

This calculator estimates plaster (render, stucco) consumption for wall plastering based on wall area, average coat thickness, mix type, substrate condition, and bag size. It supports three ways to enter area (room perimeter, single wall, or known m²) and can subtract windows and doors by total opening area or by their dimensions. Results show total treated area, total dry mix required, and the approximate number of bags.

Built-in presets reflect common mixes used indoors and outdoors, and a substrate coefficient accounts for smooth, porous, or uneven backgrounds. If your product has a different declared consumption, you can switch to manual entry.

Tips and tricks

• Area input: For rooms, the calculator uses 2 × (L+W) × H to get the total wall surface. Remember to subtract large openings so you do not overestimate material.
• How consumption is calculated: kg = Area × Thickness(mm) × Consumption(kg/m²/mm) × Substrate k; Bags = kg / Bag weight. Default presets are commonly used values in this tool: gypsum ≈ 1.0, cement ≈ 1.9, cement-lime ≈ 1.7 (all in kg/m²/mm). Substrate coefficients: smooth 1.00, porous 1.08, uneven 1.15.
• Typical thickness: Interior leveling coats often use 8-15 mm; local corrections may raise the average. Facade renders and damp rooms frequently need 10-20 mm. Start with a realistic average rather than the maximum spot thickness.
• Choosing a mix: Gypsum mixes are usually for dry, heated rooms (living areas, corridors). Cement or cement-lime mixes are typical for wet rooms (bathrooms, kitchens), basements, and exterior walls.
• Substrate notes: Porous masonry (aerated concrete, perforated brick) increases uptake, hence a higher coefficient. Very uneven brickwork or deep joints may require beacons and a larger average thickness; consider a base leveling pass.
• Practical ranges people use: Bag weights are often 20-30 kg; common average thickness for “cosmetic” leveling is about 10 mm; for rough walls 12-15 mm; for facades 15-20 mm. Many users add a small contingency (≈5-10%) if walls are highly irregular.
• European standards (informational): Indoor gypsum plasters are typically covered by EN 13279; cement and cement-lime rendering mortars by EN 998-1. Always check the manufacturer's data sheet for declared consumption and substrate preparation guidance.

FAQs

How do I pick the right input mode for area?

Use Room dimensions when you know the room's length, width, and wall height (the tool sums all four walls). Use Wall dimensions for a single wall, or Area if you already measured the surface in m².

What average thickness should I enter?

Enter the average coat thickness across the wall, not the deepest spot. A common starting point for interior leveling is 10 mm; older masonry or facades can require 12-20 mm depending on flatness.

Gypsum vs cement vs cement-lime - which preset suits my project?

For dry living spaces, gypsum plaster is widely used and easier to finish. For bathrooms, kitchens, basements, and exterior walls, people often choose cement or cement-lime renders due to moisture resistance. If your product sheet lists a different consumption, switch to manual and enter that value.

What does the substrate coefficient mean?

It adjusts consumption for background absorption/roughness: smooth = 1.00, porous = 1.08, uneven = 1.15. Porous or uneven substrates typically need a bit more material and may require priming or base leveling.

Why does my bag count show decimals?

The result is a precise estimate. In practice, round up to whole bags to cover losses and on-site variations. Many users add one extra bag for contingency, especially on uneven walls or when mixing small batches.