About This Calculator
This calculator estimates the amount of plaster needed for walls and ceilings. It calculates volume based on thickness and converts to bags required.
Coverage Guide
| Thickness | Use | Gypsum (25kg) | Lime (25kg) |
|---|---|---|---|
| 2mm | Skim coat (finish) | ~10.0 m² | ~6.8 m² |
| 3mm | Heavier skim | ~6.7 m² | ~4.5 m² |
| 10mm | Base coat (standard) | ~2.5 m² | ~1.5 m² |
| 15mm | Thick base coat | ~1.5 m² | ~1.0 m² |
| 20mm | Rough/uneven surfaces | ~1.1 m² | ~0.8 m² |
Coverage varies by plaster product and substrate. Lime systems are typically lower coverage (higher consumption) than gypsum. Always check manufacturer data sheets for final ordering.
Types of Plaster
- Skim Coat: Thin finish layer over existing plaster or plasterboard
- Multi-finish: One-coat plaster for most surfaces
- Hardwall: Base coat for high-impact areas
- Bonding: For difficult surfaces like concrete
Tips for Ordering
- • Add 10-15% for wastage
- • Gypsum: one 25kg bag covers ~2.5m² at 10mm; lime: ~1.5m² at 10mm
- • Work in manageable sections - plaster sets quickly
- • Check substrate is suitable and properly prepared
Working Time
Plaster has a working time of 20-40 minutes once mixed. Only mix what you can apply in that time. Clean tools between mixes to avoid contamination.
Ready to Calculate?
Enter your wall/ceiling area and plaster thickness to get an estimate.
Open CalculatorRelated Calculators
FLFlorida Building Code
References & Sources
Standards Cited
- ASTM C842 — Standard Specification for Application of Interior Gypsum Plaster
Defines internal plaster application thicknesses, coat systems, and coverage rates - ASTM C28 — Standard Specification for Gypsum Plasters
Guidance on plaster thickness, coverage rates, and application methods
Formulas Used
- Plaster volume:
volumeM3 = wallArea x (plasterThickness / 1000)
Source: Basic geometry - Plaster weight:
weightKg = wallArea x plasterThickness x materialCoatFactorKgPerMmM2 x (1 + wastage/100)
Source: ASTM C842 — Consumption factor is derived from nominal bag coverage at 10mm for the selected material and coat system - Bags required:
bagsRequired = ceil(totalWeightKg / bagSize)
Source: Standard quantity calculation - Bag coverage:
coverageM2 = bagSizeKg / (thicknessMm x materialCoatFactorKgPerMmM2)
Source: ASTM C842 — Coverage varies by both material type (gypsum vs lime) and coat system
Key Assumptions
- Gypsum nominal coverage per 25kg at 10mm: finish 2.0 m2, base 2.5 m2, heavy 2.3 m2 — ASTM C842 / manufacturer data-sheet practice
- Lime nominal coverage per 25kg at 10mm: finish 1.7 m2, base 1.5 m2, heavy 1.3 m2 (conservative planning values) — ASTM C28 / manufacturer data-sheet practice
- If coat system is omitted, calculator infers from thickness: <=3mm finish skim, 4-14mm base undercoat, >=15mm heavy undercoat — ASTM C842
- Typical wastage allowance of 10-15% for plaster — Industry standard practice