Why is the same spray gun quoted at 30 per cent in one place and 75 in another?

Because transfer efficiency is not a property of the gun on its own — it is the result of a TEST, and the tests do not agree. The same HVLP gun is reported at 25 to 32 per cent when measured one way and at 70 to 78 per cent when measured another, and neither figure is a lie: they were produced by different procedures, spraying different targets, at different distances, with different definitions of what counts as deposited. ASTM D5286 measures under general production conditions, D5009 and D5327 under laboratory conditions, and a laboratory panel held at a fixed distance is a far kinder target than a real one. The practical consequence is that a transfer efficiency with no method attached tells you almost nothing, and comparing two figures from different sources is comparing two different experiments. If a supplier quotes one, the useful question is which standard produced it. If you need a number you can rely on for your own work, the only real answer is a production measurement on the work itself.

Why does the hose matter so much on a small job?

Because it is the only loss here that does not scale. Overspray is a percentage — double the job and you double the overspray — but the material used to fill the line between the pump and the gun is a fixed volume set by the hose, not by the work. Fifteen metres of three-eighths inch hose holds a bit over a litre. Against twenty litres landing on the work that is around five per cent and barely worth noticing; against three litres landing it is more than a third as much again, and it is the difference between finishing and a second trip to the merchant. The effect gets worse with bore rather than with length, because volume goes with the square of the diameter: a half-inch hose holds four times what a quarter-inch one of the same length does. The practical moves are to use the shortest run that reaches, to use the smallest bore the pump and the coating will tolerate, and on genuinely small work to consider whether spraying is worth charging a line for at all.

Is ordering the cautious end just wasting money?

Less than the alternative costs, and the reason is specific to coatings rather than general caution. Run short of a brushed emulsion and you buy another tin; run short of a sprayed finish and the tin you buy is from a different batch, which is the exact problem the boxing calculator exists to prevent — tinted paint is matched to a tolerance, and a fresh batch introduced partway up a wall shows as a soft vertical step that nothing will hide afterwards. On a sprayed job it is worse still, because spraying is what you do when you want no visible joins at all. The overrun costs a part-used tin, which on most products keeps for the touch-ups you will need anyway. The shortfall can cost a repaint of the whole elevation. That asymmetry is why the headline figure here is the pessimistic end of the band and the optimistic end sits in the breakdown, rather than the other way round.

What actually moves transfer efficiency on site?

The shape of what you are spraying, more than anything else, and then the operator. A flat wall gives almost everything that leaves the gun something to land on. A handrail, a lattice, a pipe rack or a chain-link fence gives it very little, and the material that misses is gone — on genuinely open work even good equipment can put more into the air than onto the steel, which is why those jobs are so often brushed instead despite the labour. After geometry come the things the operator controls: distance from the work, keeping the gun perpendicular rather than arcing it, triggering at the ends of each pass rather than spraying past them, and not using more atomising pressure than the coating needs. Equipment class, the one thing this calculator can actually know, is the coarsest factor of the three. That is the honest reason the answer is a band: the calculator knows the least important variable and cannot see the other two.

Materials & Quantities

Paint and Coating Overspray Transfer Efficiency Calculator

How much coating to buy once overspray and the material left charging the hose are counted, starting from the quantity that has to end up on the surface.

Answers as you typeNo submit button
Every formula citedNamed published standards
Calculated in your browserNo account, nothing uploaded

SettingsSettings for this calculationUS

Market

Imperial · sales tax

Coating that must end up on the surface

The quantity a coverage calculation says the job needs.

Take this from whichever coverage page fits the work — the exterior paint, primer or steel primer calculators all produce it. Those figures count only the coating that reaches the surface and say so; this page adds what never gets there. Do not add your own waste allowance first, or it will be counted twice.

How it is being applied

The equipment class, which sets the efficiency band.

Equipment class is the coarsest of the things that decide transfer efficiency, and it is the only one a calculator can know. Distance, angle, fan width, how much of the target is edge rather than face, and the operator all move the result further than the choice between two spray classes does — which is why the answer here is a band and not a number.

Length of hose to be charged

The whole run from pump to gun. Zero for brush and roller.

Every metre of it has to be full of coating before any reaches the surface, and at the end of the job most of that is flushed out. Include extension hoses and the whip at the gun. This is ignored for brush and roller work, which has no line to charge.

Hose bore

Internal diameter of the line.

Bore matters more than length does, because the volume goes with the SQUARE of the diameter: a half-inch hose holds four times what a quarter-inch one of the same length holds. Airless hose is sold by internal diameter in inches almost everywhere, so the metric equivalents are given alongside rather than instead.

Coating to order

13 gal

Low confidence

At 40% to 70% transfer efficiency, 5.0 gal on the surface needs 7.4 gal to 12.8 gal bought — you are ordering about 2.6 times what lands. 0.3 gal of that is the hose, which does not shrink if the job does. Airless lays material down fast and is the usual choice for large areas, but its published efficiency spans a very wide range and falls hard on small or intricate work.

Coating that must land on the surface: 5 gal
If it goes well (the efficient end): 7.42 gal
Never reaches the surface (the cautious end): 7.78 gal
Held in the hose: 0.28 gal
Transfer efficiency band used: 40 to 70%
Bought per unit that lands: 2.56 times

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

ASTM D5286 defines TRANSFER EFFICIENCY as the ratio of paint SOLIDS deposited to the total paint solids used, expressed as a percent, measured under general production conditions; ASTM D5009 and D5327 are the corresponding laboratory methods
The bands used here are PLANNING figures spanning values commonly published for each equipment class, not a measurement of any particular gun. Published figures differ enormously with the test method — the same HVLP gun is reported at 25 to 32 per cent under one standard and 70 to 78 under another — so a transfer efficiency quoted without its method is not comparable to anything
Material used to charge the hose is a FIXED loss rather than a proportional one: it is the internal volume of the line, πr²L, and it does not shrink with the job. On a small job it can exceed the overspray

Inputs used

Coating that must end up on the surface: 5 gal
How it is being applied: Airless
Length of hose to be charged: 49 ft
Hose bore: 3/8 in (about 10 mm) — the common airless hose

Intermediate steps

Coating that must land on the surface: 5 gal
If it goes well (the efficient end): 7.42 gal
Never reaches the surface (the cautious end): 7.78 gal
Held in the hose: 0.28 gal
Transfer efficiency band used: 40 to 70%
Bought per unit that lands: 2.56 times

Final result12.78 gal

Confidence note: At 40% to 70% transfer efficiency, 5.0 gal on the surface needs 7.4 gal to 12.8 gal bought — you are ordering about 2.6 times what lands. 0.3 gal of that is the hose, which does not shrink if the job does. Airless lays material down fast and is the usual choice for large areas, but its published efficiency spans a very wide range and falls hard on small or intricate work.

What this calculation does not cover

Transfer efficiency is defined on SOLIDS, not on liquid. ASTM D5286 puts it as the ratio of paint solids deposited to the total paint solids used. Dividing a liquid volume by it, as this page does, is only valid because it is one paint on both sides of the division — the same figure must never be carried across to a different product, or a different thinning, without going back to solids.
The bands here are PLANNING figures spanning commonly published values, and they are not a measurement of your equipment. Published figures disagree with each other enormously, and the largest single reason is the test method: the same HVLP gun is reported at 25 to 32 per cent under one standard and at 70 to 78 under another. A transfer efficiency quoted without the method that produced it cannot be compared with one that names it.
Equipment class is the coarsest of the things that set the real number, and the only one a calculator can know. The operator, the distance and angle held, the fan width, and above all how much of the target is EDGE rather than face move it further than the choice between two spray classes does. A handrail, a lattice or a pipe rack wastes a far greater share than a flat wall, because most of what leaves the gun has nothing to hit.
Outdoors, wind removes material that no equipment class accounts for, and it does so unpredictably. Spraying in anything more than a light breeze also puts the coating somewhere it was not intended to go, which is a liability question rather than a quantity one.
The hose figure assumes the line is charged once and flushed once. Some of that material is recoverable on some jobs and none of it is on others, and nothing here covers what stays in the pump, the filters or the pot — all real, all product-specific.
AIRLESS EQUIPMENT INJECTS. An airless gun atomises by forcing coating through a small orifice at a pressure high enough to drive it through skin without breaking it open, and a fluid injection injury looks like a pinprick and is a surgical emergency — the material spreads along the tendon sheath and the damage is done in hours, not days. It is not a puncture wound and must not be treated as one; anyone injected needs a hospital told what the coating was, with the data sheet taken along. The tip guard and the trigger lock are on the gun for this and not for tidiness. None of that is a quantity question, which is why this page names the hazard and stops there.
Some sectors are required by regulation to use demonstrably high-efficiency equipment, and the threshold, the qualifying equipment and the evidence needed are set where you are working. That is a compliance question with its own paperwork, and a quantity calculator is the wrong place to answer it.

Estimated cost — your price

Price per gal ($)

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-15 · v1.0.0

Regulatory standards & verification citations3

ASTM D5286 defines TRANSFER EFFICIENCY as the ratio of paint SOLIDS deposited to the total paint solids used, expressed as a percent, measured under general production conditions; ASTM D5009 and D5327 are the corresponding laboratory methods
The bands used here are PLANNING figures spanning values commonly published for each equipment class, not a measurement of any particular gun. Published figures differ enormously with the test method — the same HVLP gun is reported at 25 to 32 per cent under one standard and 70 to 78 under another — so a transfer efficiency quoted without its method is not comparable to anything
Material used to charge the hose is a FIXED loss rather than a proportional one: it is the internal volume of the line, πr²L, and it does not shrink with the job. On a small job it can exceed the overspray

Which documents these citations point at

Standards referenced: ASTM D5286, ASTM D5009 (ASTM International, United States).

Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To spray-apply a coating. Generic types, no brands, no prices.

Protection this work requires

A dust mask does nothing about solvent vapour: ventilate through, and use an organic-vapour (A1) cartridge respirator in an enclosed room.
Nailing, chiselling and cutting all throw fragments: glasses to EN 166 or ANSI Z87.1, and goggles rather than glasses overhead.

Show the 3 tools this job needs

Essential

Airless paint sprayer
Dust sheets and masking

Recommended

Brushes

Also needed as materials: masking tape, plastic sheeting.

what each painting tool is for, and the spec that decides which to buy where one does.

How to calculate paint and coating overspray transfer efficiency in 5 steps

Coating that must end up on the surfaceThe quantity a coverage calculation says the job needs.
How it is being appliedThe equipment class, which sets the efficiency band.
Length of hose to be chargedThe whole run from pump to gun. Zero for brush and roller.
Hose boreInternal diameter of the line.
Coating to orderThe tool computes the coating to order from those figures and shows the formula, its sources, and a confidence rating alongside it.

Coating to order by coating that must end up on the surface

Page defaults, not your figures above.

Coating that must end up on the surface	Coating to order (gal)
4 gal	10.3
6 gal	15.3
8 gal	20.3
10 gal	25.3

Frequently asked questions

Why is the same spray gun quoted at 30 per cent in one place and 75 in another?: Because transfer efficiency is not a property of the gun on its own — it is the result of a TEST, and the tests do not agree. The same HVLP gun is reported at 25 to 32 per cent when measured one way and at 70 to 78 per cent when measured another, and neither figure is a lie: they were produced by different procedures, spraying different targets, at different distances, with different definitions of what counts as deposited. ASTM D5286 measures under general production conditions, D5009 and D5327 under laboratory conditions, and a laboratory panel held at a fixed distance is a far kinder target than a real one. The practical consequence is that a transfer efficiency with no method attached tells you almost nothing, and comparing two figures from different sources is comparing two different experiments. If a supplier quotes one, the useful question is which standard produced it. If you need a number you can rely on for your own work, the only real answer is a production measurement on the work itself.
Why does the hose matter so much on a small job?: Because it is the only loss here that does not scale. Overspray is a percentage — double the job and you double the overspray — but the material used to fill the line between the pump and the gun is a fixed volume set by the hose, not by the work. Fifteen metres of three-eighths inch hose holds a bit over a litre. Against twenty litres landing on the work that is around five per cent and barely worth noticing; against three litres landing it is more than a third as much again, and it is the difference between finishing and a second trip to the merchant. The effect gets worse with bore rather than with length, because volume goes with the square of the diameter: a half-inch hose holds four times what a quarter-inch one of the same length does. The practical moves are to use the shortest run that reaches, to use the smallest bore the pump and the coating will tolerate, and on genuinely small work to consider whether spraying is worth charging a line for at all.
Is ordering the cautious end just wasting money?: Less than the alternative costs, and the reason is specific to coatings rather than general caution. Run short of a brushed emulsion and you buy another tin; run short of a sprayed finish and the tin you buy is from a different batch, which is the exact problem the boxing calculator exists to prevent — tinted paint is matched to a tolerance, and a fresh batch introduced partway up a wall shows as a soft vertical step that nothing will hide afterwards. On a sprayed job it is worse still, because spraying is what you do when you want no visible joins at all. The overrun costs a part-used tin, which on most products keeps for the touch-ups you will need anyway. The shortfall can cost a repaint of the whole elevation. That asymmetry is why the headline figure here is the pessimistic end of the band and the optimistic end sits in the breakdown, rather than the other way round.
What actually moves transfer efficiency on site?: The shape of what you are spraying, more than anything else, and then the operator. A flat wall gives almost everything that leaves the gun something to land on. A handrail, a lattice, a pipe rack or a chain-link fence gives it very little, and the material that misses is gone — on genuinely open work even good equipment can put more into the air than onto the steel, which is why those jobs are so often brushed instead despite the labour. After geometry come the things the operator controls: distance from the work, keeping the gun perpendicular rather than arcing it, triggering at the ends of each pass rather than spraying past them, and not using more atomising pressure than the coating needs. Equipment class, the one thing this calculator can actually know, is the coarsest factor of the three. That is the honest reason the answer is a band: the calculator knows the least important variable and cannot see the other two.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.