Calculate the exact quantities of cement, sand, and water needed for wall and ceiling plastering. Get bag counts, material weights, and cost estimates for any mix ratio.
Optional: Deduct Openings
Thickness is within recommended range (10-15mm). Typical: 12mm
Mix Ratio Information
Standard internal wall plastering
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Planning to plaster walls or ceilings? Our plaster calculator tells you exactly how much cement, sand, and water you need. Get accurate material quantities for any mix ratio, compare different plaster types, and estimate costs before starting your project.
A plaster calculator determines the quantities of cement, sand, and water needed to plaster a given wall area at a specified thickness. It accounts for the dry volume factor (35% increase for shrinkage), mix ratios, and different plaster applications. The calculator helps you avoid over-ordering materials while ensuring you have enough for the job.
Plaster Volume Formula
Dry Volume = Wall Area × Thickness × 1.35Calculate for 1:3, 1:4, 1:5, or 1:6 cement-sand ratios with guidance on which ratio suits your application.
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.
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.
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 at 12mm thickness with 1:5 ratio, you need approximately 0.5-0.6 bags of 50kg cement. At 1:4 ratio, it's about 0.7-0.8 bags. Our calculator gives exact quantities based on 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).