Enter wall details
Example data table
| Wall size | Openings | Thickness | Mix | Waste | Estimated cement (bags) | Estimated sand (m³) |
|---|---|---|---|---|---|---|
| 5 m × 3 m (1 wall) | 1.5 m² | 12 mm | 1:4 | 10% | ≈ 1.70 | ≈ 0.17 |
| 8 m × 3 m (2 walls) | 3.0 m² | 15 mm | 1:5 | 12% | ≈ 4.05 | ≈ 0.42 |
| 12 ft × 10 ft (1 wall) | 15 ft² | 0.5 in | 1:4 | 10% | ≈ 1.10 | ≈ 0.11 |
| 20 ft × 10 ft (2 walls) | 30 ft² | 0.6 in | 1:6 | 8% | ≈ 2.90 | ≈ 0.34 |
Formula used
Sand volume = Vdry × (Sand part / Total parts)
Bags = Cement kg / Bag weight
Water liters ≈ Cement kg × (w/c ratio)
Apply wastage: Multiply totals by (1 + Wastage%/100)
How to use this calculator
- Select your unit system and enter wall length and height.
- Set the number of similar walls, and subtract openings area.
- Choose plaster thickness, sides plastered, and number of coats.
- Enter the mortar mix ratio and adjust dry factor if needed.
- Add a wastage percentage to cover losses and spillage.
- Optionally enable cost estimate and enter local prices.
- Press Calculate to view results and download CSV/PDF.
Professional guide to wall plaster estimating
1) Why accurate plaster quantities matter
Plaster is often purchased in bags of cement plus loose sand, so small measuring errors can create real cost and schedule impacts. A shortfall can stop finishing trades, while overbuying ties up cash and creates disposal waste. Estimating with consistent inputs keeps procurement predictable.
2) Area measurement with openings
Start with wall face area: length × height, then multiply by the number of similar walls. Subtract door and window openings to get net plaster area. If you plaster both sides of a wall, double the net area. If you apply multiple coats, multiply again by the coat count.
3) Thickness and coat planning
Typical interior plaster thickness ranges around 10–15 mm for smooth finishes, while external work and levelling can push higher. Thickness drives volume directly: area × thickness. Two thinner coats can improve bond and reduce cracking risk compared with one thick coat on uneven substrates.
4) Wet to dry mortar conversion
Mortar volume expands when converted from compacted wet volume to dry ingredients because of voids and bulking. A dry factor near 1.27–1.35 is widely used for practical estimating; this calculator defaults to 1.33. Adjust it if your sand grading or site practice differs.
5) Mix ratio and material split
The mix ratio sets the cement-to-sand proportion, for example 1:4 or 1:5. The calculator divides total dry mortar volume by total parts, then allocates cement and sand by their parts. Richer mixes (lower sand part) increase cement demand and usually cost more per square meter.
6) Cement bags, density, and water
Cement is converted from volume to mass using bulk density, commonly near 1440 kg/m³. Bags are then computed from cement mass and your chosen bag weight, often 50 kg. Water demand is estimated from water–cement ratio; a practical range is about 0.40–0.60 depending on workability.
7) Wastage allowance and site reality
Even with careful batching, some mortar is lost to spillage, rebound, and leftover pans. A wastage allowance of 5–15% is common, increasing for tall scaffolding, hot conditions, or frequent mixing interruptions. This calculator applies wastage to cement, sand, water, and volumes for a safer purchase plan.
8) Turning quantities into a clear budget
When you enable cost estimating, the tool multiplies cement bags and sand volume by your local unit prices, then adds labor per m². A small misc/transport percentage helps cover loading, handling, and local delivery. Save results as CSV for quoting, or export PDF for site records and approvals.
FAQs
1) Should I enter net area or total wall area?
Enter total wall dimensions and subtract openings area. The calculator handles net area, sides, and coats, so you get consistent results across multiple walls.
2) What dry factor should I use for plaster mortar?
A common estimating range is 1.27 to 1.35. Use 1.33 as a practical default, then adjust based on your sand bulking, compaction, and mixing practice.
3) How do I choose plaster thickness?
For smooth interior finishes, 10–15 mm is typical. Uneven masonry, external exposure, and levelling needs can require more. Measure trial patches if the substrate varies.
4) Why are cement bags sometimes not a whole number?
The tool calculates continuous quantities from volume and density. In purchasing, round up to the next full bag to avoid shortages, especially when wastage is higher.
5) Does the water output replace on-site judgment?
No. It is a planning estimate based on a water–cement ratio. Actual water depends on sand moisture, weather, additives, and the finish required. Mix to workable consistency.
6) Can I use this for both sides and multiple coats?
Yes. Select both sides if plaster is applied on each face, and increase coats for multi-layer work. The calculator multiplies net area accordingly before computing volumes.
7) How should I set wastage percentage?
Start around 8–12% for typical residential plastering. Increase it for high lifts, many small batches, or rough surfaces. Reduce it only when site controls are proven.
Notes and good practice
- Dry factor varies with bulking, compaction, and workmanship.
- Thicker coats and rough substrates usually increase consumption.
- Water demand changes with sand grading and weather conditions.
- Accurate plaster estimates help reduce waste and delays significantly.