Plaster Quantity Calculator
Calculate Cement & Sand for wall plastering with deductions for doors and windows.
No deductions added. Click "Add" to subtract door/window areas.
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What is a Plaster Quantity Calculator?
A Plaster Quantity Calculator helps you estimate the exact amount of Cement and Sand needed for wall plastering. Plastering is the process of applying a smooth mortar coat on walls to protect masonry and create a paintable surface.
Calculating plaster materials involves the 1.6 Dry Volume Factor – a crucial adjustment that accounts for volume shrinkage when dry materials are mixed with water, plus the filling of joints and surface irregularities. Without this factor, you'll significantly underestimate your material needs.
Our advanced calculator supports multiple walls, allows door and window deductions, offers 4 mix ratios for different applications, and includes cost estimation to help you budget your plastering project accurately.
4 Surface Types
Internal Wall (12mm), External Wall (20mm), Ceiling, and Repair work. Each sets appropriate thickness and mix ratio automatically.
Multiple Walls
Add multiple wall dimensions in one calculation. Perfect for estimating an entire room or multiple rooms at once.
Deductions Feature
Subtract door and window areas from your calculation. Avoid over-ordering and save material costs significantly.
4 Mix Ratios
Choose 1:3 (Rich), 1:4 (Strong), 1:5 (Standard), or 1:6 (Lean) based on application. Each has different cement requirements.
How to Use the Plaster Calculator
Select Surface Type
Choose Internal Wall (12mm, 1:6), External Wall (20mm, 1:4), Ceiling (12mm, 1:4), or Repair (15mm, 1:3). This auto-sets recommended settings.
Enter Wall Dimensions
Input Length and Height for each wall. Click "Add Wall" to add more walls. Results update in real-time.
Deduct Openings
Click "Add" under Deductions. Enter door and window dimensions. These areas will be subtracted from total.
Get Results & Cost
See cement bags and sand quantity. Enter material prices for cost estimation. Download or Print your calculation.
Understanding the 1.6 Factor
When dry cement and sand are mixed with water, the volume shrinks by 33% because cement particles fill the voids between sand grains. Additionally, plaster must fill brick joints and surface irregularities.
The 1.6 Dry Volume Factor combines:
- 1.33× for dry-to-wet volume shrinkage
- Additional 20% for joint filling
- Combined factor: approximately 1.6
For 1 m² of 12mm plaster, dry volume = 0.012 m³ × 1.6 = 0.0192 m³
Mix Ratio Selection Guide
The mix ratio (Cement:Sand) determines strength and cost. Richer mixes (more cement) are stronger but more expensive and prone to cracking.
| Ratio | Type | Best For |
|---|---|---|
| 1:3 | Rich | External walls, repair, basement |
| 1:4 | Strong | Ceilings, external walls |
| 1:5 | Standard | Internal brick walls |
| 1:6 | Lean | Internal smooth walls (common) |
Plaster Thickness Guidelines
| Application | Thickness | Mix Ratio | Notes |
|---|---|---|---|
| Internal Walls | 12mm | 1:5 or 1:6 | Single coat application |
| External Walls | 20mm | 1:4 | Apply in two coats (12mm + 8mm) |
| Ceilings | 12mm | 1:4 | Apply POP coat over plaster |
| Repair/Patch | 15-20mm | 1:3 | Match existing thickness |
| Rough RCC | 6mm | 1:3 | Just to even out surface |
Pro Tips for Quality Plastering
Wet the wall first - Dry walls absorb water from mortar, causing weak bond and cracks.
Apply in two coats - For thickness over 12mm, apply as 12mm base + finish coat.
Cure for 7 days - Spray water 2-3 times daily or cover with wet jute to prevent cracking.
Use clean sand - Clay and silt in sand reduce adhesion. Wash if necessary.
Avoid rich mix - Too much cement causes shrinkage cracks. Stick to recommended ratios.
Use chicken mesh - Fix wire mesh at RCC-brick joints to prevent junction cracks.
Common Use Cases
New Construction
Calculate materials for entire house - internal and external walls. Use deductions for all doors and windows.
Single Room
Estimate for bathroom, bedroom, or kitchen renovation. Add all 4 walls and deduct door/window areas.
Repair Work
Calculate materials for patching damaged plaster. Use 1:3 rich mix for better bonding with old surface.
Frequently Asked Questions
What is the dry volume factor 1.6 in plaster calculation?
When cement and sand are mixed with water, the volume shrinks. The dry volume factor 1.6 accounts for this shrinkage plus filling of joints and depressions in the wall. It means you need 60% more material than the theoretical wet volume. Formula: Dry Volume = Wet Volume × 1.6
What thickness should I use for plastering?
Standard plaster thickness: 12mm (0.5 inch) for internal walls - provides smooth finish for painting. 15mm for rough surfaces. 20mm (0.75 inch) for external walls - provides better weather protection and waterproofing. Ceiling plaster is typically 12mm.
What is the best cement-sand ratio for plastering?
1:3 (Rich Mix) - For external walls, repair work, and areas with heavy weathering. 1:4 - For ceilings and external walls where strength is important. 1:5 - Standard for internal brick walls. 1:6 (Lean Mix) - For internal smooth walls. Richer mixes use more cement and are stronger but more expensive.
How many cement bags for 100 sq ft plastering?
For 100 sq ft (9.3 m²) with 12mm thickness and 1:6 ratio: approximately 1.5-2 bags of cement and 3-4 cubic feet of sand. For 20mm external plaster with 1:4 ratio: approximately 2.5-3 bags of cement. These estimates include the 1.6 dry volume factor and 10% wastage.
Should I deduct door and window areas from plaster calculation?
Yes! Always deduct door and window openings to avoid over-ordering materials. A standard door (3×7 ft = 21 sq ft) and window (4×4 ft = 16 sq ft) can save significant material in a room. Our calculator has a dedicated deduction feature for this purpose.
What is the wastage percentage for plastering?
Standard wastage for plastering is 10-15%. This accounts for fallen mortar, uneven application, and handling losses. For rough brick walls, use 15-20%. For smooth concrete block walls, 10% is usually sufficient. Our calculator has an adjustable wastage slider.
How much water is needed for plastering?
Water requirement is approximately 20-25% of cement weight for workable mortar consistency. For 50kg cement bag, use 10-12 liters of water. Too much water weakens the plaster and causes cracking. Always add water gradually and mix to proper consistency.
What type of sand is best for plastering?
Fine sand (river sand or manufactured sand) is best for plastering. It should be clean, free from clay and organic matter. Grain size should pass through 4.75mm sieve. Avoid using sea sand due to salt content. M-sand (manufactured sand) is increasingly used as river sand alternative.
How long should I cure plaster?
Plaster should be cured for minimum 7 days. Start curing after initial set (6-8 hours). Spray water 2-3 times daily or cover with wet jute/burlap. Proper curing prevents cracking and ensures full strength development. External plaster may need longer curing in hot weather.
What causes plaster to crack?
Common causes: 1) Rich mix (too much cement) - use correct ratio. 2) Thick application in single coat - apply in 2 coats for >12mm. 3) Insufficient curing - cure for 7+ days. 4) Too much water in mix - use proper consistency. 5) Plastering on dry wall - wet the wall before application.