Understanding your result
The headline is the extra paint spraying needs, and the sub-line gives both totals and the extra cost. The three figures show the roller quantity, the sprayer quantity and the application time the sprayer saves, and the bars compare the two quantities at a glance.
The table starts with the paint that ends up on the surface, the same for both methods, then the roller quantity with its loss and cans, the sprayer quantity with its overspray, conditions and cans, the extra paint, the paint cost of each and the difference, and the application hours of each. The note puts the paint and the hours together, which is the actual decision.
The hours here are application only. The painting time calculator adds prep and setup, which is where spraying’s masking goes; the sprayer usage calculator works out the spraying minutes and refills from the tip flow; and the paint cost calculator prices either quantity with supplies and tax.
How we calculate this
The losses are shares of the paint that leaves the can, so the quantity is divided by what remains: 20% overspray means 80% reaches the wall, and the paint needed is the surface figure divided by 0.8, which is 25% more, not 20%. This is how coating and spray-equipment makers state transfer efficiency, and it is the same arithmetic as the spread rate calculator’s transfer-efficiency line.
The overspray presets are mid-range figures from sprayer makers’ and contractors’ guidance: 20% for interior walls and ceilings in still air, 35% outside with some wind, 40% at fine-finish settings on narrow work. The application rates are the site’s production rates, listed on the production rates page. The spraying versus rolling guide explains where each method’s paint goes and when the trade favours each.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Roller and tray loss | 5% | Paint left in the cover and tray; a round figure |
| Overspray, interior | 20% | Mid-range of the 20–25% airless figures in sprayer makers’ guidance |
| Overspray, exterior | 35% | Mid-range of the 30–40% outside in some wind |
| Overspray, fine finish | 40% | Narrow work at fine-finish settings |
| Back-rolling | + 5% | Paint picked up by the back-roller; site estimate |
| Application rates | roller 200, sprayer 600 sq ft per hour per coat | Site production rates |
| Coverage and price | 350 sq ft per gallon, $40 a gallon | Site defaults |
Assumptions last reviewed October 8, 2026.
The calculator does not model the paint left in the sprayer’s hose and pump at the end of the job, which can be a quart or more on a 50 ft hose, or the cleaning time. It does not price the sprayer rental, the masking materials or the drop cloths. Those belong in the supplies and time calculators.
Two worked examples
An empty room’s walls and ceiling
1,000 sq ft, two coats, 350 sq ft per gallon, interior spraying at 20% overspray, paint at $40.
- On the surface: 1,000 ÷ 350 × 2 = 5.71 gallons
- Roller: 5.71 ÷ 0.95 = 6.02 gallons; sprayer: 5.71 ÷ 0.80 = 7.14 gallons
- Extra paint: 1.13 gallons, $45.11
- Application: roller 10 h, sprayer 3 h 20 min
Forty-five dollars of paint to save over six hours on an empty room is a good trade, if the masking takes less than the six hours.
A house exterior, back-rolled
2,500 sq ft, two coats, exterior spraying at 35% overspray, back-rolled.
- On the surface: 14.29 gallons
- Roller: 15.04 gallons; sprayer: 14.29 ÷ 0.65 × 1.05 = 23.08 gallons
- Extra paint: 8.04 gallons, $321.57
- Application: roller 25 h, sprayer 8 h 20 min
Outdoors the paint penalty is large, and the note on wind applies. A professional crew still sprays, because sixteen hours of labour costs more than eight gallons.
Where to find your inputs
Area and coats. From the wall, ceiling or exterior calculators and the coats calculator.
Coverage. From the can; the same figure for both methods.
Conditions. Interior and still, exterior with some wind, or fine-finish work. If you have measured your own loss, use the custom figure.
Back-rolling. Tick it for rough siding, block, stucco and new drywall.
Price. Per gallon, from the shelf.
Common mistakes
- Adding 20% instead of dividing by 0.8. A 20% loss means 25% more paint.
- Forgetting the masking. The sprayer’s time saving is before it.
- Spraying in wind. The overspray lands on cars and neighbours.
- Skipping back-rolling on texture. The paint bridges the hollows instead of filling them.
- Comparing quantities with different coats. Keep the coats the same for both.
- Forgetting the hose. A long hose holds paint you will not get back.
Questions people ask
- How much more paint does spraying use?
- Indoors on walls and ceilings, about 20% of airless spray is overspray, so a job needing 5.7 gallons on the wall takes 7.1 gallons sprayed against 6.0 rolled. Outdoors with some wind, 35% overspray makes it half as much again as rolling. Fine-finish settings on doors and trim lose about 40%.
- Is spraying faster than rolling?
- On the wall, about three times faster. The calculator uses 200 sq ft per hour per coat for rolling with cutting in and 600 for airless spraying. Masking, which spraying needs and rolling mostly does not, is not included, and on a furnished room it can take longer than the time saved.
- What is back-rolling?
- Rolling over sprayed paint while it is wet, to push it into texture and even the finish. It is standard on rough siding, block and new drywall. The roller picks up a little paint, which the calculator counts as an extra 5%.
- Does a sprayed finish hide better?
- Usually, because a sprayer lays a thicker, more even wet film in one pass than a roller does. It is not a reason to skip the second coat on a colour change.
- When is spraying worth it?
- Empty rooms, new construction, exteriors, ceilings with texture, fences and anything with many edges, such as louvered doors and railings. Rolling wins in furnished rooms, for single walls, and where overspray would land on something valuable.
- What overspray figure should I use?
- The presets are 20% for interior walls and ceilings, 35% for exterior work in some wind and 40% for fine-finish settings on trim and doors. If you know your own rig's loss, choose your own figure and enter it.