Rendering Calculator – Bags, Coats, Coverage & Cost

MEASURE · RENDER · PLAN

Rendering calculator for walls, gables, bags and job costs

This free rendering calculator estimates whole bags or tubs for measured exterior surfaces. Use it for one wall, several elevations, a gable end or repeated sections. It supports manufacturer coverage, consumption by weight and mixed yield, with an optional second product for a separate base coat, finish or colour. Mesh, stock and pricing are optional.

The shortest route is to enter Product A’s coverage and thickness, add your wall dimensions and calculate. You do not need to price labour or configure a complete render system to get quantities. The result explains each order, including rounding and any existing stock.

How to use the rendering calculator

1. Choose Metric or Imperial measurements. Currency changes the money display only.
2. Select the product-data method that matches your bag, tub or technical sheet. Enter product coverage and the corresponding thickness basis.
3. Enter the wall dimensions, or choose direct area. For a gable, enter the rectangular wall height and the additional triangular rise separately.
4. Deduct openings and add any reveal returns that will be rendered. Quantity repeats the entire surface, including its openings and reveals.
5. Add another surface, use bulk entry, or override thickness on a particular elevation. Blank overrides inherit; zero excludes that product.
6. Enable Product B only for a separately purchased product. Add deliberate allowances, matching stock, optional mesh and prices as needed.
7. Calculate and check the shopping list. Print / Save PDF opens a free estimate containing the results and working.

Which coverage method should I choose?

Coverage per bag or tub at reference thickness suits a product sheet giving square metres covered by one purchase unit. At the same total and reference thickness, the calculation is simply area divided by coverage. Different thicknesses are scaled proportionally for quantity estimation; that does not mean every thickness is permitted. Thin-coat grain sizes need their own stated coverage, rather than assuming proportional scaling between textures.

Consumption in kg per m² per mm uses a product-specific consumption rate, thickness and bag weight. The engine calculates the mass required before dividing by the weight in one bag. Enter the rate exactly as specified: kg/m² for an entire coat is different from kg/m²/mm. A whole-coat figure should instead be converted to coverage per bag at that coat thickness.

Mixed yield in litres per bag uses the volume of usable wet render produced by one bag. One square metre at one millimetre thickness is one litre. This method uses applied wet thickness. It does not split a traditional site mix into sand, cement and lime or decide a mix ratio.

Applied thickness, finished thickness and scraping

Always match the thickness basis to the coverage figure. A manufacturer may give coverage for a finished scraped coat while allowing for the extra material applied before scraping. Adding that allowance again would inflate the estimate. Other figures describe applied material only. Read the actual product guidance and use an additional waste allowance for losses not already included.

For example, Weber describes roughly one square metre per 25 kg bag for a particular scraped weberpral finish, with material applied thicker before scraping. That is a product/finish example, not a universal bag yield. K Rend also publishes product-specific consumption rates. The calculator starts with coverage blank so you can use the correct data for your chosen system.

Worked example: a wall with an opening

A wall 5 m wide and 4 m high has a gross area of 20 m². Deduct a 2 m² opening and add 1 m² of rendered reveals: net area is 19 m². With coverage of 1 m² per bag at the same reference and total thickness, the base requirement is 19 bags. Add 10% extra to reach 20.9, then round up to 21 whole bags. With one matching whole bag already available, buy 20. These coverage values are an arithmetic example; check your own product.

Measuring gables and reveal returns

Gable mode combines a rectangle and a triangle: wall width × rectangular wall height, plus wall width × triangular rise ÷ 2. Do not enter the full ridge height as the rectangular height. For an irregular elevation, split it into non-overlapping simple surfaces or enter an independently measured area.

Openings are deducted from the face, but window and door returns may add rendering area. Measure each coated return’s length and depth, multiply them, and add the results. Do not include a sill or head that will receive a different finish. Use a separate surface with its own thickness override if the reveals require a different build-up. Four-wall mode is a perimeter shortcut; confirm all four faces actually need rendering.

Two products, multiple passes and separate orders

A scratch/base coat and a different finishing product need separate coverage and purchase rounding. Product B provides that second order. It initially covers all surfaces when enabled; set a surface’s B thickness to zero to exclude it. The same product applied in several passes normally belongs in one product section with its combined thickness. Splitting it across A and B would round purchases separately.

Pool only matching product, colour and pack size. More than two distinct products or colours need separate estimates. Existing stock reduces the quantity to buy, but this calculator assigns it no historical cost. Additional whole units can represent pump residue, a reserve or another known loss; do not include the same loss again in your percentage allowance.

Mesh and the full job price

Optional mesh estimates whole rolls using effective coverage after overlaps. By default it covers net surfaces once, irrespective of the number of render products. Use the area override for selected surfaces or specified additional reinforcement patches. The tool does not decide mesh type, position, laps or corner reinforcement.

Choose labour per net area for one whole-job area rate, or per product-coated area to count A and B separately. Neither basis counts trowel passes or adds material waste. Hour/day pricing is useful for uneven backgrounds, difficult details, access and preparation. Add beads, primer, protection, delivery or scaffold under other costs where applicable. Those quantities depend on detailing and are not inferred from wall area.

Markup adds a percentage to materials, labour and other costs; it is not profit margin. Tax applies to the marked-up amount. Use consistent pretax input prices, then enter the tax percentage relevant to your estimate. Changing currency does not convert prices.

Frequently asked questions

Manufacturer references

See Weber’s render coverage explanation and K Rend K Mono product guidance for examples of product-specific data. Check the latest technical sheet for the actual product, finish and application.

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