Estimate how much paint you need for walls, ceilings or a room — metric or imperial, with optional primer and cost.
Surface
Calculation method
Coverage varies by paint brand, product line, sheen and surface — always use the figure printed on your specific product's label rather than a generic assumption.
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Choose your surface — walls only, ceiling only, or walls and ceiling together — then pick a method. Room dimensions works for a single rectangular room: enter length, width and wall height and the calculator finds the wall and/or ceiling area automatically. Custom wall sections lets you add each wall (or an L-shaped or multi-room layout) as its own width × height entry, which is useful for irregular rooms, hallways or feature walls. If you're painting walls, you can subtract doors, windows and other openings so you're not buying paint for surfaces you won't cover. Enter the number of coats, your paint's coverage rate from the product label, a container size, and a waste allowance, and the calculator rounds up to a whole number of containers to buy.
The amount of paint you need depends on three things: the net area you're painting (after subtracting doors and windows), how many coats you're applying, and your paint's coverage rate. As a rough guide, a typical interior wall paint covers around 10 m² per litre (roughly 350–400 sq ft per US gallon) per coat, but this varies significantly by brand, sheen and the surface you're painting onto — always check the figure printed on your can. For an average 4m × 3.5m bedroom with 2.4m ceilings and two coats, most people need one to two 4-litre containers, or a single US gallon can for a similarly sized room. Use the calculator above with your product's actual coverage rate for an accurate figure rather than a generic rule of thumb.
Coverage rate tells you how much wall area one unit of paint (a litre or a gallon) will cover in a single coat. It's printed on the paint can, usually as a range (for example "10–12 m² per litre" or "350–400 sq ft per gallon"), because coverage depends on the porosity and texture of the surface — a smooth, previously painted wall covers more than bare or textured plaster. When a range is given, using the lower figure gives a safer (slightly higher) quantity estimate.
Most interior painting uses two coats for even colour and hide, especially over a colour change, a repair, or bare drywall/plaster. A single coat may be enough for a straightforward repaint in a similar colour. The formula the calculator uses is:
A waste allowance (5–15% is typical, 10% is a common default) is then added on top to account for spillage, roller loading, cutting-in and touch-ups, before rounding up to the nearest whole container.
Primer is optional in the calculator and is priced and calculated separately from your topcoat paint, because primer coverage rates are usually different from finish paint. Primer is generally recommended when painting bare drywall or plaster, covering a stain, making a major colour change (especially light to dark or vice versa), or painting over a glossy or previously unpainted surface. If you're doing a straightforward repaint in a similar colour over sound existing paint, primer is often unnecessary. Enter your primer's coverage rate from its own product label — don't reuse your topcoat's coverage figure, as the two are rarely the same.
Paint is sold in fixed container sizes, so the calculator always rounds your raw litres or gallons up to a whole number of containers — you can't buy 1.3 tins of paint. Common metric sizes are 1L, 4L, 10L, 15L and 20L; common imperial sizes are quarts, 1-gallon and 5-gallon pails. Buying one larger container is often more cost-effective than several small ones, but check the total against what you'll actually use — leftover paint is useful for touch-ups but ties up money if you consistently over-buy.
The Cost tab gives a simple material-cost estimate: containers needed × price per container, for paint and (if enabled) primer separately. This does not include labour, brushes, rollers, trays, masking tape, drop sheets, filler/sanding supplies or delivery charges — add these separately if you need a full project budget. Prices for paint vary widely by brand and finish, so use your local supplier's actual quoted price for an accurate total.
Example 1 — Metric, walls only. A bedroom is 4m × 3.5m with 2.4m ceilings, walls only, with one 0.9m × 2.1m door. Gross wall area = 2×(4×2.4) + 2×(3.5×2.4) = 36.00 m². Subtracting the door (1.89 m²) gives a net area of 34.11 m². At two coats and a coverage rate of 10 m²/L, raw paint needed = (34.11 × 2) ÷ 10 = 6.82 L. Adding 10% waste gives 7.50 L, which rounds up to two 4-litre containers.
Example 2 — Imperial, walls and ceiling. A 12ft × 10ft room with 8ft ceilings is painted walls and ceiling, one coat, no openings subtracted, 0% waste. Wall area = 2×(12×8) + 2×(10×8) = 352 ft². Ceiling area = 12×10 = 120 ft². Gross/net area = 472 ft². At a coverage rate of 350 sq ft per gallon, raw paint needed = 472 ÷ 350 = 1.35 gal, which rounds up to two 1-gallon containers.
The most common mistake is forgetting to subtract doors and windows from wall area, which leads to over-buying — though this shouldn't be done for a ceiling-only calculation, since a ceiling has no doors or windows to subtract. Another is using a single average coverage figure for every product rather than the number on the specific can being bought, since coverage can vary by 20% or more between brands and sheens. A third is skipping the waste allowance entirely, which often leaves just short of a second coat on a larger room. Finally, treating primer and topcoat coverage as identical typically produces an inaccurate primer estimate, since primers often cover less area per litre than finish paints.
This calculator provides a material quantity estimate based on area, coats and the coverage rate you enter — it does not know your specific paint product, surface condition, or application method (roller, brush or sprayer), all of which affect real-world coverage. It assumes a consistent coverage rate across the whole surface, which may not hold for heavily textured, damaged or highly porous walls. It does not account for multiple colours on the same wall, feature walls calculated separately, or paint lost to colour-matching test pots. For a large or high-value project, confirm quantities with your paint supplier before purchasing.
It depends on the net area you're painting (after subtracting doors/windows), the number of coats, and your paint's coverage rate. Use the calculator above with the coverage rate from your paint can for an accurate figure — as a rough guide, a typical 4m × 3.5m bedroom with two coats needs one to two 4-litre containers.
Most interior paints cover roughly 350–400 square feet per gallon per coat, though this varies by brand, sheen and surface. Check the exact figure printed on your paint can and enter it into the calculator's coverage rate field for an accurate quantity.
An average bedroom (around 4m × 3.5m with 2.4m ceilings) needs roughly 7–8 litres of paint for two coats on the walls, which is one to two 4-litre containers depending on openings. Use the Room dimensions method above with your room's actual measurements for a precise result.
A 10ft × 10ft room with 8ft ceilings has about 320 sq ft of wall area. At two coats and 350 sq ft/gallon coverage, that's roughly 1.8 gallons raw, which rounds up to two 1-gallon containers (or one 5-gallon pail if you're painting several similar rooms).
Two coats are recommended for most jobs, especially over a colour change, bare drywall, or a repair, since a single coat often leaves patchy coverage. One coat can be enough for a simple repaint in a similar or lighter-to-slightly-different shade over sound existing paint.
Primer quantity is calculated the same way as paint — net area × coats ÷ coverage rate — but using your primer's own coverage figure, which is often lower than your topcoat's. Enable the Primer tab in the calculator and enter your primer product's coverage rate for an accurate quantity.
This depends on the room's wall (and optionally ceiling) area, number of coats, and your paint's coverage rate. Enter your room's dimensions into the calculator above to get a precise gallon or litre figure, then round up to whole containers as shown in the results.
Yes, for wall paint — subtracting doors and windows avoids over-buying, since you won't be painting those surfaces. This doesn't apply to a ceiling-only calculation, since ceilings don't have doors or windows to subtract.
Material cost per square foot depends on your paint's price and coverage rate — divide the price per container by the area it covers (accounting for coats). Use the Cost tab above with your local paint price to get a total material estimate for your specific room; labour is priced separately.
This depends on how much paint you need in total — a single larger container (such as a 10L or 5-gallon pail) is often more economical than several small ones if you'll use most of it. The calculator rounds your quantity up to whole containers of the size you select, so try a couple of sizes to compare.
Yes — select Walls + Ceiling to calculate both together, or Ceiling only to calculate just the ceiling. Ceiling paint quantity is not affected by door or window openings, since those are wall features.