Calculate the exact cement, sand, and water needed for wall and ceiling plastering. Get bag counts, material weights, and costs for any mix ratio.
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Planning to plaster walls or ceilings? This calculator covers both gypsum plaster (yeso) — the quantity in kilograms and bags per square meter for interior work — and traditional cement-sand render for exterior and heavy-duty jobs. Enter your area and thickness to get exact material quantities, bag counts and an optional cost estimate.
A plaster calculator works out how much material a plastering job needs. For gypsum plaster the yield is about 0.8–1.0 kg per square meter per millimeter of thickness, so total kilograms = net area (m²) × thickness (mm) × yield. For cement-sand render it converts the wet plaster volume (area × thickness) to a dry volume (×1.35 for shrinkage and wastage), then splits it into cement and sand by the mix ratio. Both modes subtract door and window openings first.
Plaster Volume Formula
Calculate materials for plastering newly built walls in residential or commercial construction projects.
Estimate plaster needs when renovating bedrooms, living rooms, or other interior spaces in existing buildings.
Plan stronger plaster mixes for moisture-prone areas requiring water-resistant finishes.
Calculate weather-resistant render materials for external walls and facades.
Determine lighter plaster quantities for ceiling applications with appropriate thickness.
Estimate materials for repairing damaged plaster sections or patching holes in existing walls.
Generate accurate material estimates for construction bids and project proposals.
Help homeowners calculate exact material needs for do-it-yourself plastering projects.
Calculate gypsum (yeso) quantity per m² for interior walls and ceilings, or cement-sand render for external and heavy-duty plastering.
Get recommendations for internal walls, external renders, and ceiling plastering with appropriate thickness ranges.
See cement requirements in 50kg, 40kg, and 25kg bag quantities—order exactly what you need.
Automatically subtract door and window areas to avoid over-ordering materials for your project.
Get approximate material costs to help budget your plastering project accurately.
Use pre-configured settings for bedrooms, bathrooms, kitchens, and exterior walls for quick estimates.
Gypsum plaster consumption is about 0.8–1.0 kg per square meter for every millimeter of thickness. At a typical 13 mm coat that is roughly 12 kg/m², so a 25 kg bag covers about 2 m². Multiply your net wall area (m²) by thickness (mm) by ~0.9 to get the total kilograms.
For 40 m² of wall at 13 mm thickness you need about 40 × 13 × 0.9 ≈ 468 kg, or roughly nineteen 25 kg bags. Enter your exact area and thickness above and the calculator returns 25 kg and 40 kg bag counts plus the water needed.
For interior walls, a 1:5 or 1:6 cement-sand ratio is typically used. These ratios provide adequate strength while being economical. Use 1:5 for general interior work and 1:6 for finish coats. For bathrooms and kitchens where moisture resistance is important, consider 1:4.
External walls require stronger plaster to withstand weather. Use 1:3 or 1:4 cement-sand ratio for exterior renders. The 1:3 ratio is best for areas exposed to heavy rain or extreme weather, while 1:4 works well for protected exterior surfaces.
Standard plaster thickness is 12-15mm for internal walls and 15-20mm for external walls. Ceiling plaster is typically 6-12mm. Applying plaster too thick (over 20mm) in one coat can cause cracking, so thick applications should be done in multiple coats.
When cement and sand are mixed with water, the fine cement particles fill voids between sand grains. This compaction means the dry materials occupy more space than the finished plaster. The 1.35 factor accounts for this shrinkage plus normal wastage during application.
For 100 sq ft (≈9.3 m²) at 12 mm with a 1:5 mix you need about 0.7 of a 50 kg cement bag — round up to 1 bag — plus roughly 0.13 m³ of sand. Our calculator gives exact quantities for your specific area, thickness and mix ratio.
Sand quantity depends on the mix ratio. For 1:4 ratio, you need 4 parts sand per 1 part cement (approximately 180 kg sand per 50kg cement bag). For 1:5 ratio, it's 5 parts sand (225 kg). For 1:6 ratio, use 6 parts sand (270 kg per bag).
Yes, but the wall must be clean, free of loose material, and dampened before plastering. Hack smooth surfaces to improve adhesion. For very smooth surfaces like concrete blocks, apply a splatter dash coat (1:2 cement-sand thrown onto the wall) and let it cure for 24 hours before plastering.
Plaster needs at least 7 days to cure for initial strength, but 28 days is recommended for full curing before painting. Keep the plaster moist by sprinkling water 2-3 times daily for the first week. Painting too early can trap moisture and cause paint failure.
Common causes include: too much cement (strong mix), thick application in single coat, rapid drying, poor surface preparation, or movement in the structure. To prevent cracking, use appropriate mix ratios, apply in thin coats, keep plaster moist during curing, and ensure structural stability.
For bathrooms, external walls, and areas exposed to moisture, adding waterproofing compound is recommended. Use as per manufacturer instructions, typically 1-2% by weight of cement. This helps prevent water penetration and efflorescence (white salt deposits).