Calculators
Paint coverage and conversion calculators
The arithmetic every other calculator relies on: square footage, coverage rates, coats, cans and units.
The number on the can is a laboratory figure: a measured film on a smooth, sealed panel. Real coverage is lower because walls are porous and textured, rollers hold paint, and the first coat always goes further into the surface than the second. Everything on this site starts from an editable coverage rate for that reason, and this group holds the calculators that deal with the rate itself: converting it, deriving it from volume solids and film thickness, and turning it into cans.
The unit conversions are exact. A US gallon is 3.785411784 litres, a square foot is 0.09290304 square metres, and 350 square feet per gallon is 8.6 square metres per litre. The conversion pages print the factors so you can check the arithmetic by hand.
10 calculators
Paint Coverage Calculator
Area a quantity of paint covers, or paint for an area, with a texture factor and coats.
Wall Square Footage Calculator
Paintable area of up to six walls and a ceiling, with the openings subtracted, in sq ft and m².
Paint Quantity Converter
Gallons, quarts, pints, fluid ounces, litres and millilitres, converted exactly and rounded to cans.
How Many Coats Calculator
How many coats a colour change takes, whether to prime, and how much extra paint that means.
Spread Rate & Film Thickness Calculator
Theoretical and practical coverage from volume solids and dry film thickness, the way pros spec it.
Paint Thinning Calculator
How much water or thinner to add for a given percentage, and whether it is within the label limit.
Spray vs Roll Paint Usage Calculator
Paint and cost by roller and by airless sprayer for the same job, with the overspray shown.
Can Size Optimizer
The cheapest mix of pails, gallons and quarts (or litre cans) for the paint you need at your prices.
Paint Weight Calculator
What a quantity of paint weighs with its cans, the trips to carry it, or the paint left in a can by weight.
Sample Pot Calculator
How many sample pots to test your colours with proper patches, and what they cost.
Guides for this topic
Airless spray tips explained: the three digits
A 517 tip sprays a 10 inch fan through a 0.017 inch hole. Once you can read the number, choosing a tip for any paint and any pump takes a minute.
Dark colours, LRV and the extra coats they cost
A navy wall can take half as much paint again as a pale one. The number on the back of the paint chip tells you before you buy, and a tinted primer is usually the way round it.
Wet film, dry film and volume solids: coverage for pros
Every coverage figure on a can comes from one line of arithmetic. Learn it and you can compare paints honestly, check a crew's film build, and predict coverage for any coating.
How many coats of paint you really need
The number of coats changes the order more than any other input. Here are the rules, the reasons behind them, and the cheaper way round a third coat.
How much paint do I need? The complete method
Five steps turn a tape measure and a paint can label into an order that will not run short, and a worked room shows each of them with real numbers.
Measuring a room for paint (and what to subtract)
Ten minutes with a tape measure is all a paint estimate needs, if you measure the right things and subtract only what is worth subtracting.
Paint can sizes, 5-gallon savings and the leftover problem
The cheapest way to buy 3.6 gallons is four gallons, not three and three quarts. A little arithmetic on can prices saves money, and a plan for the leftover saves the next repair.
Paint coverage explained: why 400 sq ft a gallon rarely happens
The coverage on the can is a laboratory number. Here is what eats into it on a real wall, by how much, and which figure to plan with instead.
Primer: when you need it and when you can skip it
Primer is either essential or a waste of a day, depending on the surface. Here is how to tell which, which primer to buy, and how much.
Spraying vs rolling: paint usage, overspray and finish
A sprayer is several times faster at putting paint on a wall and always uses more paint doing it. Whether it saves time on your job depends on the masking, not the spraying.
Textured and popcorn ceilings: coverage, product and technique
A popcorn ceiling can take two thirds more paint than a smooth one of the same size. Here is why, how to plan for it, and how to paint it without pulling the texture down.
Trim, doors and windows: the quart maths
Trim is a small area and a lot of work. Here is how to turn linear feet and door counts into quarts, and why the answer is usually two or three quarts more than people think.
Questions people ask
- How many square feet does a gallon of paint cover?
- Manufacturers' data sheets for interior wall paint typically print 350 to 400 sq ft per gallon per coat on a smooth, previously painted surface. Bare drywall, textured walls and rough exterior wood bring it down to 250 to 300, and elastomeric or block-filler products are applied so thick that 50 to 100 sq ft per gallon is normal.
- How many square metres does a litre cover?
- 350 sq ft per gallon is 8.6 m² per litre and 400 sq ft per gallon is 9.8 m² per litre. European emulsion cans commonly quote 10 to 14 m² per litre; the difference is partly thinner films and partly the same optimism about smooth test panels.
- How many quarts are in a gallon, and how big is a 5-gallon pail?
- Four US quarts make a gallon. A quart is 32 US fluid ounces or 0.946 litres, a gallon is 3.785 litres and a 5-gallon pail is 18.9 litres. Sample pots are usually 8 fl oz, a quarter of a quart, and cover roughly 10 sq ft at two coats, enough for a 2 × 2 ft test patch with some to spare.
- How many coats of paint do I need?
- Two for any change of colour, any new or patched surface, or any change of sheen. One coat can refresh the same colour over sound paint. Deep reds, yellows and oranges over a light wall, or a light colour over a dark one, often take three unless the primer is tinted. The coats calculator applies those rules.
- Does a 5-gallon pail save money?
- Per gallon, a pail is usually cheaper than five single cans, but only if you will use most of it: the leftover is wasted money and a storage problem. The can size optimizer compares your store's prices for pails, gallons and quarts and finds the cheapest combination that covers the quantity you need.
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