The short answer
At 350 square feet per gallon, 1,000 square feet of wall takes 2.9 gallons per coat. Two coats is 5.8, so you buy 6 gallons — or better, a 5 gallon pail and a single gallon, which is usually $30 cheaper than six separate gallons.
Add one gallon if any of this applies: new drywall, textured walls, a colour change of more than two shades, or spraying instead of rolling. Add two if more than one applies.
Before anything else, be sure which 1,000 square feet you mean. Wall area and floor area are different numbers and confusing them is the most common paint estimating error there is. A 1,000 square foot apartment has roughly 2,400 to 3,000 square feet of wall. Put your actual room dimensions into the paint calculator and it will do the wall arithmetic, subtract the openings and round to the half gallon.
The quick way to check yourself: add up the perimeter of every room in feet and multiply by the ceiling height. A 1,000 square foot single-storey house typically has 280 to 340 linear feet of wall, which at 8 feet is 2,240 to 2,720 square feet of paintable surface.
Coverage in practice
The 350 to 400 square feet on the can is measured on smooth, sealed, previously painted drywall with a professional roller. It is achievable. It is also the best case.
| Surface | Coverage | Gallons for 1,000 sq ft, 2 coats |
|---|---|---|
| Smooth, previously painted drywall | 350 sq ft | 6 |
| New drywall, primed | 320 sq ft | 6.5 |
| New drywall, unprimed | 250 sq ft | 8 |
| Light orange peel texture | 300 sq ft | 7 |
| Knockdown texture | 275 sq ft | 7.5 |
| Rough sawn wood or cedar | 180 sq ft | 11 |
| Bare masonry or brick | 175 sq ft | 11.5 |
Spraying changes every row in that table by 15% to 20% in the wrong direction. Spray atomises paint into the air and some of it never reaches the wall, and the film it lays down is thinner than a rolled one. Spray for speed on big empty rooms, roll for economy.
Texture and porosity
Texture increases the actual surface area. A knockdown wall measured as 100 square feet has perhaps 125 square feet of paintable surface once you follow the peaks and valleys, and the roller has to work into all of it.
Porosity is the other half. Fresh joint compound is far more absorbent than the paper face of the board around it, which is why an unprimed patch shows through two coats of finish paint as a dull spot — the phenomenon painters call flashing. A coat of primer over the patches, or over the whole wall on new board, evens the absorption out and saves a coat of the expensive material.
The nap of the roller is the variable people never adjust. On smooth drywall use 3/8 inch; on light texture 1/2 inch; on knockdown or masonry 3/4 inch. A 1/4 inch nap on a textured wall lays a film so thin you will need three coats, and no amount of extra paint in the tray fixes it.
Colour change and coats
Coverage is about volume; hide is about pigment. A paint can have excellent coverage and poor hide, which is exactly what happens with deep saturated colours.
| Going from | Going to | Coats |
|---|---|---|
| Mid grey | Mid beige | 2 |
| White | Mid tone | 2 |
| Dark navy | White | Tinted primer + 2 |
| White | Deep red or yellow | Tinted primer + 2 to 3 |
| Any | Same colour, touch-up | 1 |
Deep reds, oranges and yellows are the difficult cases because they are made on a clear or near-clear base with very little white pigment. A grey tinted primer underneath does more than a third coat of colour and costs a third as much. The full decision tree is in how many coats of paint.
Ceiling and trim
Ceilings are measured as the floor footprint. A 1,000 square foot house has about 1,000 square feet of ceiling, which at two coats is 6 gallons of flat ceiling paint — the same order of magnitude as the walls, and it is routinely forgotten in the budget.
Trim is linear, not square. Figure one gallon of trim enamel per 300 linear feet for two coats. A 1,000 square foot house typically has 400 to 600 linear feet of baseboard, casing and door edges, so 2 gallons. Doors are counted separately: a gallon does about eight door faces with two coats, so six doors painted both sides is most of a gallon on its own.
If you are also replacing the trim, measure it with the method in the baseboard and trim measuring guide and prime the sticks before they go on the wall.
Order the whole job in one go, in this sequence:
- Work out wall area room by room and total it.
- Add ceilings as the floor area of the rooms you are doing.
- Convert both to gallons at the coverage for your surface, times the coats.
- Add trim by linear feet, and doors by the face.
- Round up to whole gallons, then to a pail if the total passes four.
One last ordering note. Past four gallons, buy the 5 gallon pail: it is typically 15% to 20% cheaper per gallon and it removes the tint variation between cans, which on a long uninterrupted wall is visible in raking light. If you do buy separate gallons, box them — pour them all into one pail and mix before you start.
And if the walls are new board, the drywall and the paint are one job with one schedule. Sheet counts and compound quantities are in how many sheets of drywall.
Frequently asked questions
How many gallons of paint for 1,000 square feet of wall?
About 3 gallons per coat at 350 square feet per gallon, so 6 gallons for the usual two coats. Buy 5 gallon pails once you pass 4 gallons — the price per gallon drops sharply.
Is 1,000 square feet the floor area or the wall area?
These are different numbers and mixing them up is the most common paint estimating error. A 1,000 square foot house has roughly 2,400 to 3,000 square feet of wall surface to paint.
Does the colour change how much paint I need?
Yes. Deep reds, yellows and oranges use a low-hide base and often need three coats. A tinted primer in the same family saves a full coat on the whole room.
Should I buy a 5 gallon pail or single gallons?
Past four gallons, buy the pail. It is typically 15% to 20% cheaper per gallon and every drop is the same tint, which matters on a long uninterrupted wall. Single gallons vary slightly between cans, which is why painters box them together before starting.