Understanding your result
The headline is the paint to buy, overspray included, and the sub-line gives the cans and the spraying time. The three figures show the overspray, the spraying time and the buckets.
The table follows the paint through the sprayer: what ends up on the surface, the overspray added, the paint to buy, the thinner if any, the volume through the gun, the trigger minutes at the tip’s flow, the spraying time at your trigger share and the number of buckets. The trigger minutes are a floor: no technique gets the paint out faster than the tip allows.
The sprayer is one side of a decision. The spray versus roll calculator puts this quantity next to rolling; the spray tip calculator picks the tip and checks it against the pump; the thinning calculator measures the thinner; and the spread rate calculator turns a data sheet’s film thickness into coverage.
How we calculate this
The overspray presets are 20% for interior walls and ceilings, 35% outside with some wind and 40% for fine-finish work on doors and trim, mid-range figures from sprayer makers’ and contractors’ guidance; dividing by what reaches the wall is the same arithmetic as the transfer efficiency in the film thickness calculator. The tip flows are the water flows at 2,000 psi from the main sprayer makers’ tip charts, listed on the spray tip page; the spray tips guide explains how orifice size sets flow.
Spraying time here is gun time only. Masking, setup, flushing and cleaning the pump are separate, and the production rates guide explains how pros allow for them.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Overspray | 20 / 35 / 40% | Sprayer makers’ and contractors’ guidance for interior, exterior and fine finish |
| Tip flows | .015 0.24, .017 0.31, .019 0.38, .021 0.47 gpm | Water at 2,000 psi from Graco, Titan and Wagner tip charts, rounded |
| Trigger share | 60% | Typical for walls; site figure |
| Coverage | 350 sq ft per gallon | Interior wall paint data sheets |
| Bucket | 5 gallons | The pail the pump’s suction tube sits in |
Assumptions last reviewed October 8, 2026.
The calculator does not model the paint left in the pump and hose at the end of the job, which can be a quart or more on a 50 ft hose, flushing water, or the slower flow of thick paint. It is gun time, not job time.
Two worked examples
An empty house interior with a 517 tip
2,000 sq ft of walls and ceilings, two coats at 350 sq ft per gallon, 20% overspray, no thinning, 60% trigger time.
- On the surface: 2,000 ÷ 350 × 2 = 11.43 gallons
- Paint: 11.43 ÷ 0.8 = 14.29 gallons, three 5-gallon pails
- Trigger time: 14.29 ÷ 0.31 = 46 minutes; spraying time 1 h 17 min
- Buckets: 3
An hour and a quarter of spraying for two coats on a whole floor is why pros spray new construction; the masking around it is the rest of the day.
A house exterior with a 519 tip
3,000 sq ft, two coats, 35% overspray, 5% thinning.
- On the surface: 17.14 gallons; paint: 17.14 ÷ 0.65 = 26.37 gallons
- Through the gun: 26.37 × 1.05 = 27.69 gallons
- Trigger time: 27.69 ÷ 0.38 = 73 minutes; spraying time 2 h 1 min; 6 buckets
Nine gallons of overspray is the price of the speed outdoors, which is why calm days and shields matter.
Where to find your inputs
Area, coats and coverage. From the quantity calculators and the can.
Conditions. Indoors in still air, outdoors with some wind, or narrow work at a fine-finish setting.
Tip. The three-digit number on the tip; the last two digits are the orifice.
Trigger share. About 60% on open walls; 30 to 40% on trim, doors and cut-up work.
Bucket. The container the suction tube draws from.
Common mistakes
- Pressure too high. It adds overspray without adding speed.
- A worn tip. The fan narrows and wastes paint.
- Thinning to make a small pump cope. Use a smaller tip within the material’s range instead.
- Letting the bucket run dry. The pump sucks air and spits.
- Forgetting back-rolling on texture. It adds a little paint and a lot of adhesion.
- Comparing spray time with roll time and ignoring masking. The masking is where spraying’s time goes.
Questions people ask
- How much paint does an airless sprayer use?
- The paint for the surface plus the overspray. For 2,000 sq ft at two coats and 350 sq ft per gallon, 11.4 gallons reach the wall; with 20% overspray indoors the sprayer uses 14.3 gallons, three 5-gallon pails.
- How long does it take to spray a gallon?
- At a 517 tip's flow of about 0.31 gallons a minute of water at 2,000 psi, just over three minutes of trigger time. With the trigger pulled about 60% of the time, a gallon is about five and a half minutes of spraying. Paint flows a little slower than water.
- What is overspray?
- The paint that does not land on the surface, meaning mist that drifts, droplets that bounce, and the fan that passes the edge of a door or a railing. About 20% indoors on walls, 30 to 40% outside in some wind and on narrow work.
- Should I thin paint for an airless sprayer?
- Most modern airless sprayers spray latex unthinned with the right tip. Thinning is for small pumps or cold weather, within the label limit, usually 10% at most. Each percent of thinner adds volume through the gun without adding paint to the wall.
- What does trigger time mean?
- The share of the working time the gun is actually spraying. The rest is moving along the wall, checking edges, moving the hose, refilling and wiping the tip. 50 to 70% is typical for walls; much less for trim and doors.
- How many buckets will I fill?
- Through-the-gun volume divided by the bucket size, rounded up. A 14 gallon job from 5-gallon buckets is three fills; keep the next bucket stirred and ready so the pump never runs dry and sucks air.