Estimate how many liters of paint you need for a wall or room.
Paint needed = (wall area × number of coats) ÷ coverage rate per liter.
The figure you'll see quoted everywhere — around 100 sq ft per litre — is a single-coat number on a smooth, primed masonry wall, and almost no real paint job stops at one coat. For two coats of a standard emulsion (tractor-emulsion grade), practical coverage in Indian conditions is closer to 130–150 sq ft per litre; premium emulsions (Royale-tier) run 110–130 sq ft per litre in practice even though the tin often claims 140–160; and distemper, being thinner-bodied and more absorbent, drops to 40–50 sq ft per litre for two coats. Whichever paint you're using, budget from the two-coat figure, not the one-coat headline number on the packaging.
Wall texture changes coverage more than most people expect — a rough or textured wall can pull coverage down to 70–80 sq ft per litre even for a paint rated at 100, because more paint physically sinks into the surface irregularities. Also budget separately for a primer coat on new plaster or a major colour change (dark to light, or the reverse), since primer isn't optional in those cases and skipping it usually means a third topcoat to get even coverage anyway — which costs more paint than the primer would have.
Take the paint's single-coat coverage figure and roughly halve it for two coats — so a paint claiming 130–150 sq ft/litre for two coats is really about 260–300 sq ft/litre for one. Manufacturers usually publish the two-coat figure directly on the tin; use that number rather than the sometimes higher one-coat marketing figure.
Yes, meaningfully. A smooth, well-plastered wall can get 100 sq ft per litre on the first coat; a textured or rough-plastered wall on the same paint can drop to 70–80 sq ft per litre because the surface absorbs more paint into its irregularities. If your walls are textured, add 15–25% to whatever the smooth-wall figure suggests.
New plaster, bare walls, and major colour changes (especially dark-to-light) generally need a primer coat first. Skipping it on these surfaces usually means the topcoat absorbs unevenly and needs a third coat to look consistent — at which point you've used more paint than the primer would have cost.
Distemper is a thinner, more porous, water-based coating compared to emulsion, so it spreads thinner and absorbs faster into the wall surface. That's why its two-coat coverage (40–50 sq ft/litre) is roughly a third of a standard emulsion's (130–150 sq ft/litre) — it's a genuine product difference, not a measurement error.