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About this tool
Find primer litres required by primer type, substrate absorbency and coat count, with tin sizes and cost.
This calculator gives the litres of primer a job needs from the formula litres = area × coats ÷ (spreading rate × absorbency factor). The spreading rate is the figure printed on the tin — around 100-120 sq ft per litre per coat for Indian wall primers — and the absorbency factor scales it for what you are actually priming, so fresh cement plaster at 0.78 and AAC block at 0.60 use far more than the smooth plaster the published rate assumes. You also get the cheapest tin combination, the thinner range and the material cost.
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Read the result and use it in your planning or reporting.
Eight substrate factors, from non-absorbent metal at 1.20 down to rough masonry at 0.60.
The least primer bought, and the fewest tins, with the cost of each.
Shows the thinning range for the primer family without inflating the litres you buy.
About 9.5 litres for one coat on smooth cement plaster with a 5% wastage allowance, using a wall primer rated at 110 sq ft per litre per coat. On new bare plaster the same 1000 sq ft takes roughly 12 litres and on AAC block or rough masonry closer to 16, because the porous surface absorbs part of the film.
One full coat is the standard specification for a wall primer over prepared plaster or putty. A second coat is worth it only on very porous new masonry, over patch repairs, or where a strong existing colour would otherwise bleed through — priming twice does not substitute for a topcoat.
Follow the tin: Indian water-based interior wall primers are usually thinned 30-50% by volume with clean water, exterior water-based primers 20-30%, solvent-based cement primer 30-40% with mineral turpentine, and metal or wood primers only 10-20%. Thinner does not reduce the litres of primer you must buy, because the published coverage is already quoted for the thinned material.
Not on a fresh or repaired surface. Primer seals a porous substrate so the topcoat's binder stays on the surface instead of soaking in, gives uniform absorption so the finish sheen is even, and provides adhesion on plaster, metal and wood. An extra coat of emulsion is more expensive per litre and does none of those jobs.
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