A plasterer is pricing a 180 m2 external sand-cement render job on a new brick veneer house. Before submitting the quote, they need the total product weight, bag count and a cross-check of the 15mm average thickness assumption.
Render & Screed Calculator
Masonry
Coverage varies by product and application thickness. Typical rates:
Sand-cement render (15mm): ~25–30 kg/m² · Acrylic base coat (5mm): ~8–10 kg/m²
Texture/finish coat (3mm): ~3–5 kg/m² · Floor screed (50mm): ~70–80 kg/m²
Always check manufacturer's TDS (Technical Data Sheet) for exact coverage — products vary significantly.
Sand-cement render (15mm): ~25–30 kg/m² · Acrylic base coat (5mm): ~8–10 kg/m²
Texture/finish coat (3mm): ~3–5 kg/m² · Floor screed (50mm): ~70–80 kg/m²
Always check manufacturer's TDS (Technical Data Sheet) for exact coverage — products vary significantly.
Reference: Product manufacturer TDS — USG Boral, Rockcote, Mapei, Laticrete
Results are estimates for planning purposes. Verify with current standards and a qualified professional.
1 What this calculator does
Calculates the quantity of render or screed in kilograms and bags from the area to be covered and the product type. Supports sand-cement render (15mm), acrylic render (5mm), texture coat (3mm), floor screed (50mm) and thin-set screed (25mm). Includes 8% waste.
2 Formula & professional reasoning
Approximate kg per m2 by product type:
Sand-cement render 15mm: ~27 kg/m2
Acrylic render 5mm: ~9 kg/m2
Texture coat 3mm: ~4 kg/m2
Floor screed 50mm: ~75 kg/m2
Thin-set screed 25mm: ~38 kg/m2
Total kg = Area x kg/m2 x 1.08 (8% waste)
Bags = Ceiling(Total kg / Bag size)
Product consumption depends on thickness and product density. Sand-cement render at 15mm uses approximately 27 kg/m2 because the dry density of the mixed mortar is approximately 1,800 kg/m3 (1,800 x 0.015 = 27). The 8% waste factor accounts for material lost in mixing and application, over-application in hollows, and any re-rendering of defective patches. Floor screed at 50mm uses 75 kg/m2 at a density of approximately 1,500 kg/m3 (1,500 x 0.050 = 75). Verify against the specific product data sheet as premixed products vary.
3 Worked examples
⚠️ Illustrative example only — not clinical or professional instruction.
Basic
External sand-cement render on brick veneer
Given: Area: 180 m2 | Product: sand-cement render 15mm | Bag size: 20 kg | Waste: 8%
Working:
kg/m2: 27 | Total kg: 180 x 27 x 1.08 = 5,248.8 kg | Bags: ceiling(5248.8/20) = ceiling(262.4) = 263 bagsAnswer: 5,249 kg | 263 x 20 kg bags of render
💡 At $12-$15 per 20 kg bag, materials cost is approximately $3,150-$3,950. This is only the base coat render -- a texture coat over the top adds approximately 4 kg/m2 x 180 = 720 kg = 36 x 20 kg bags additional.
Standard
Floor screed for tile substrate
Given: Area: 75 m2 | Product: floor screed 50mm | Bag size: 20 kg | Waste: 8%
Working:
kg/m2: 75 | Total kg: 75 x 75 x 1.08 = 6,075 kg | Bags: ceiling(6075/20) = ceiling(303.75) = 304 bagsAnswer: 6,075 kg | 304 x 20 kg bags of floor screed
💡 304 bags of 20 kg is 6.08 tonnes of material -- significant delivery weight. Check that the slab can take the cumulative load and that the delivery truck can access the site. A 50mm screed over 75 m2 is a large pour -- plan the work in sections to maintain a workable mix.
Advanced
Acrylic render system -- base and texture coat
Given: Area: 240 m2 | Base coat: acrylic render 5mm (9 kg/m2) | Texture coat: 3mm (4 kg/m2) | Bag size: 20 kg
Working:
Base: 240 x 9 x 1.08 = 2,332.8 kg -> 117 bags | Texture: 240 x 4 x 1.08 = 1,036.8 kg -> 52 bags | Total: 169 bags across two productsAnswer: 117 bags base coat + 52 bags texture coat = 169 bags total | 3,370 kg total product
💡 Acrylic render systems are specified as a complete system -- base coat and texture/finish coat must be compatible products from the same manufacturer. Never mix acrylic render brands between coats.
4 Sanity check
Coverage rates by product type
Sand-cement render 15mm: 27 kg/m2 | Acrylic render 5mm: 9 kg/m2 | Texture coat 3mm: 4 kg/m2 | Floor screed 50mm: 75 kg/m2 | Thin screed 25mm: 38 kg/m2
Always verify against the product technical data sheet -- coverage rates vary between brands.
Always verify against product TDS
Premixed and polymer-modified products vary significantly from the generic rates -- some high-build products cover more per kg, others cover less
Bag weight options
Most Australian render and screed products: 20 kg bags | Some specialty products: 15 kg or 25 kg | Confirm with supplier
Render thickness considerations
Sand-cement render: typically applied in two coats (scratch coat 10mm + finish coat 5mm) | Acrylic render: single coat 5mm onto a primed background
5 Common errors
| Error | Cause | Consequence | Fix |
|---|---|---|---|
| Using a generic coverage rate without checking the specific product TDS | Assuming all sand-cement renders have the same coverage rate | Material quantity off by 10-30% -- running short or overordering significantly | Every product has a stated coverage rate on its technical data sheet (TDS). The rate in this calculator is a generic approximation. Always cross-check against the TDS of the specific product being specified. |
| Not accounting for two-coat render systems in the material calculation | Calculating only one coat when the spec requires two | Material order for only half the required render | Traditional sand-cement render is typically two-coat: a 10mm scratch coat scratched to provide a mechanical key, followed by a 5mm finish coat. Calculate each coat separately from its thickness. The total 15mm is split as 10mm scratch + 5mm finish, not as a single application. |
| Not applying a bonding agent or primer on smooth concrete backgrounds | Applying render directly to smooth poured concrete | Render delamination -- the smooth concrete surface has insufficient mechanical key for render adhesion | On smooth or low-suction backgrounds (poured concrete, block paving, smooth block), apply a bonding agent or PVA primer to the background before rendering. Alternatively, a cement slurry coat or proprietary dash coat can be applied first to provide the key. |
| Estimating screed volume without confirming the substrate level and required finished level | Assuming a uniform 50mm thickness across the area | Screed volume and weight significantly underestimated if the substrate is irregular | On irregular substrates, establish the finished floor level (FFL) from the drawings and measure the depth to the existing substrate at multiple points. Use the average depth across the area for material calculation, not the nominal design thickness. |
6 Reference & regulatory links
🇦🇺 Australia
7 Professional workflow
Common tools used alongside this one:
Brick & Block Calculator
Brick and Block Calculator determines the wall area that will receive render, feeding directly into this calculation
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Construction Labour Cost Calculator
Construction Labour Cost Calculator estimates the plastering or screeding labour from the calculated area and product quantities
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