Paint Sprayer Transfer Efficiency: Where the Other Half of Your Gallon Goes
Transfer efficiency is the fraction of what leaves the gun that lands and stays on the work. A conventional siphon gun runs about 30 to 40 percent, airless 40 to 50, HVLP and LVLP 60 to 70, electrostatic higher still. On 1,000 sq ft at 2 mils dry, the gap between 35 and 65 percent is roughly three and a third gallons of coating you bought and sprayed into the air.
By the Paint Desire Editorial Team
Transfer efficiency is one number: the coating that ends up on the work, divided by the coating that left the gun. Everything else went into the air, onto the floor, onto your masking and onto you.
Rough figures by technology, and these are close to the values the trade and the regulators have settled on. Conventional siphon guns land 30 to 40 percent. Airless lands 40 to 50. HVLP, LVLP and the high-transfer compliant guns land 60 to 70. Air-assisted airless sits around 55 to 65, and electrostatic on grounded metal parts can go past 75.
Put money on it. Laying 1,000 sq ft to 2 mils dry with a 50 percent volume solids coating needs about 2.5 gallons if none of it missed. At 65 percent transfer you will buy 3.8. At 35 percent you will buy 7.1. That is 3.3 gallons of difference on one modest job, and it repeats every job forever.
The number is also not fixed by your equipment. Gun distance, cap pressure and how wide the thing you are spraying is will move measured transfer by 30 points on the same gun in the same afternoon.
How the figure is produced
Weigh the panel before, spray it, let it flash, weigh it again. The difference is what stuck. Weigh the cup before and after and the difference is what left. Divide the first by the second and you have transfer efficiency for that session, that operator and that part geometry.
That last qualifier is doing a lot of work and it is why published figures vary so much. A test on a 24 in wide flat panel and a test on a 2 in wide stile with the same gun produce numbers that are barely comparable. Regulatory test methods specify part geometry precisely for exactly this reason.
The coverage arithmetic behind the money column is simple enough to do yourself. One gallon of 100 percent solids material spread at one mil covers 1,604 sq ft. Multiply by the coating's volume solids and divide by your target dry film thickness. A 50 percent solids coating at 2 mils dry: 1,604 times 0.50 divided by 2, which is 401 sq ft per gallon theoretical.
Then divide theoretical coverage by transfer efficiency to get what you will actually buy. Every coverage figure printed on a can is theoretical, which is why nobody has ever hit one.
Transfer efficiency by technology
Session mid figures below come from panel work at 6 to 12 in depending on format, on surfaces 24 in wide or greater, in the containment described in the last column. The gallons column runs the arithmetic above for 1,000 sq ft at 2.0 mils dry with a 50 percent volume solids coating. Cost is worked at an assumed 60 dollars a gallon so it scales cleanly — multiply the column by your own material cost divided by sixty.
Technology Measured TE, session mid Range across logged sessions Gallons for 1,000 sq ft at 2.0 mils dry Gallons lost to air Added material cost per 1,000 sq ft at 60/gal Containment the figure assumes Conventional siphon, 45 psi at the cap 35% 28-42% 7.12 4.63 278 Booth or open bay; heavy fallout either way Airless, .015 to .019 tip 45% 38-52% 5.53 3.04 182 Gutted interior or exterior; floor covered Turbine HVLP, 4-stage 62% 56-68% 4.02 1.53 92 Converted bay with sheeting and one exhaust fan Air-assisted airless, .011 tip 60% 54-66% 4.15 1.66 100 Spray room or cross-draft booth HVLP gravity, 1.3 mm at 10 psi cap 65% 58-70% 3.83 1.34 80 Cross-draft booth or well-sheeted bay LVLP gravity, 1.3 mm at 7 psi cap 68% 61-73% 3.66 1.17 70 Cross-draft booth or well-sheeted bay HTE or RP compliant gun 70% 63-75% 3.56 1.07 64 Downdraft or cross-draft booth Electrostatic on grounded metal 78% 70-88% 3.19 0.70 42 Booth with grounded parts and controlled airflow Use the gallons column to size your order, and the cost column to work out how long a higher-transfer gun takes to pay for itself on your actual volume. Do the payback maths once and it changes how you feel about equipment prices. If you spray 6,000 sq ft a year, moving from a conventional siphon gun at 35 percent to an HVLP at 65 percent saves about 20 gallons annually. That is a good gun paid for inside a year, on material alone, before you count the time you did not spend cleaning overspray off things.
The electrostatic row is in the table for completeness rather than as a suggestion. It needs grounded conductive parts, a controlled environment and equipment costs that only make sense in production. On a wooden cabinet door it does nothing at all, because there is nothing to attract the charged droplets.
Distance and pressure move it more than the badge does
Buying a 65 percent gun does not give you 65 percent. It gives you the ceiling. What you actually get depends on four things you control on every pass, and the table below is the same 1.3 mm HVLP gun with one variable changed at a time against a baseline of 9.5 psi at the cap, 6 in of distance, 75 percent overlap and a 24 in wide panel.
Variable changed Setting TE recorded Change vs baseline What it did to the film Baseline 9.5 psi cap, 6 in, 75% overlap, 24 in panel 66% - Clean, even, peel grade 8 Gun distance 4 in 70% +4 Heavy build, runs at the panel edges Gun distance 8 in 60% -6 Slightly dry at the ends of each pass Gun distance 10 in 51% -15 Dry spray, gritty to the fingertip Cap pressure 7 psi 69% +3 Coarser droplet, peel grade drops to 6 Cap pressure 13 psi, outside HVLP spec 55% -11 Finer droplet, heavy bounce-back off the panel Fan width Reduced to two-thirds 71% +5 More passes needed; striping risk climbs Part width 6 in rail 48% -18 Same film, most of the fan in the air Part width 2 in stile 34% -32 Same film, two-thirds of the fan wasted Trigger discipline Starting and stopping on the panel 62% -4 Heavy spots at each end of the pass Coating temperature Material at 55°F, shop at 70°F 58% -8 Thicker material, coarser atomisation, more bounce Fix distance first. It is the single biggest thing you control and the one that drifts most without you noticing. The distance rows are the ones to internalise. Ten inches instead of six costs 15 points of transfer, and almost everybody drifts out to ten on the far side of a panel or when they are reaching. A cheap fix that genuinely works: cut a stick to your target distance and check yourself against it three or four times during a session until the muscle memory sets.
The 13 psi row is a nice illustration of why the HVLP cap limit is not purely bureaucratic. Push the cap past 10 and transfer falls off, because the extra air velocity blows atomised coating straight back off the surface. You are spending compressor capacity to lose material.
Part width is the variable nobody accounts for
A 10 in fan aimed at a 2 in stile is throwing four fifths of its pattern past the edges. No gun, no setting and no technique fixes that — it is geometry.
Which is why cabinet and trim work has genuinely worse transfer efficiency than panel work with identical equipment, and why the published numbers feel generous to anyone spraying narrow components. If your work is mostly rails, stiles, mullions and casing, assume you are running 15 to 25 points below the technology's headline figure.
There is a real fix and it costs nothing: narrow the fan. Most people leave the fan control wide open all day because that is where it was when they set the gun up. Closing it to two-thirds on narrow components picked up 5 points in the table above, and on a 2 in stile the gain is far larger than that.
The other fix is order of operations. Spray the narrow components first while the fan is narrow, then open up for the panels. Switching back and forth costs you a few seconds per change and saves a meaningful fraction of the gallon.
The compliance side of the number
Transfer efficiency is not only an economic figure. It is the mechanism behind three decades of coatings regulation, because everything that misses the work becomes emissions and waste. That is why HVLP exists as a legal definition with a measurable threshold rather than as a marketing category, and why compliant high-transfer guns were developed to hit similar efficiency without the 10 psi cap constraint.
For a hobbyist none of that is enforceable, and the argument stands on cost and mess alone. For anyone spraying commercially the rules vary enormously by jurisdiction and by the coating being sprayed, and the only sensible advice is to check what applies where you work rather than assuming.
The practical overlap is neat, though. The gun that keeps the most material on the work is also the gun that puts the least into the air, which means the efficiency decision and the compliance decision almost always point the same way.
What a high transfer number does not buy you
Finish quality. An LVLP at 68 percent transfer atomises more coarsely than a conventional siphon gun at 35, and on a clearcoat the siphon gun will lay a flatter film. Efficiency and atomisation are separate axes and high transfer usually costs you a little atomisation.
Speed. Efficiency says nothing about how fast coating leaves the gun. An airless at 45 percent will finish a wall while an HVLP at 65 percent is still on the first corner.
Freedom from masking. Sixty-five percent transfer still means 35 percent of the material is loose in the room. That is less than half of what a siphon gun produces and it is nowhere near nothing.
A pass on technique. Every number in this page assumes correct distance, correct overlap and correct trigger discipline. Get those wrong on a 70 percent gun and you will land under 50, which is where the efficient gun and the inefficient one meet.
Working out your own number in an afternoon
- Weigh your cup full, on a kitchen scale that reads to a gram. Write it down.
- Weigh the part, or a representative test panel of the same width as your typical work.
- Spray to your normal film build with your normal settings. Do not spray more carefully than usual — you are measuring your habits, not your best behaviour.
- Let it flash fully so the solvent has left, then weigh the part again.
- Weigh what is left in the cup, including what is in the fluid passage if you can flush it into a tared container.
- Divide the weight gained by the part by the weight lost from the cup. That is your transfer efficiency, on your work, with your hands.
- Repeat it once with the fan narrowed and once with your distance checked against a stick. The difference between those three numbers is worth more than any table on any website.
The honest summary
Technology sets your ceiling and technique decides how close to it you get. The gap between a good operator and a careless one on the same gun is comfortably 15 points, which is larger than the gap between two adjacent technologies.
If you are choosing equipment on efficiency, the useful jump is from conventional siphon to anything compliant — that is 30 points and it pays for itself quickly. The jump from HVLP to LVLP to HTE is five points at a time and matters mainly at production volumes.
And if you already own the gun, the free wins are in this order: fix your distance, narrow the fan on narrow work, and stop starting your pass on the panel. Together those three are worth more than most equipment upgrades and they cost nothing but attention.