Epoxy Floor Thickness: What Mil Means and What to Specify

Epoxy floor thickness is measured in mils, and a mil is one thousandth of an inch. A box-store kit dries to 3 to 5 mil, a professional garage build runs 20 to 30 mil, and commercial floors go to 60 mil and beyond. The number that decides how long the floor lasts is dry film thickness, not the photo on the box, because thickness predicts lifespan better than brand.

The short version

• Overview: 3 to 5 mil for a DIY kit, 20 to 30 mil for a real garage build, 60 mil and up for commercial.
• My take: Two brands can put the same resin in the bucket. What separates a floor that lasts from one that peels is how many mils end up bonded to the slab, and that lives in the spec, not the label.
• How we price: System ranges come from the EpoxyTimes rate card.

The short answer

Thickness is the single number that best predicts how an epoxy floor holds up, and almost no product page states it plainly. A mil is one thousandth of an inch, so 5 mil is 0.005 inch, thinner than a sheet of printer paper. A box-store kit rolled out in a coat or two dries to roughly 3 to 5 mil. A professional flake or solid build over a ground slab lands around 20 to 30 mil. Industrial floors run 60 mil to a quarter inch.

The catch is that the number on the can is almost never the number on your floor. Coatings are sold wet and measured dry, and depending on how much of the liquid is solid, half of it can evaporate before it cures. Below is what each system leaves behind, how to convert the wet number to the dry one, how a contractor proves it, and the one sentence to put on your quote.

Epoxy thickness by system and application

Dry film thickness is what remains bonded to the concrete after cure. These are typical dry-mil ranges by system and use, not marketing claims.

The jump that matters most is from the first row to the third. A DIY kit and a professional flake build use similar chemistry, but the build is four to six times thicker because a full broadcast means flake is thrown into the wet coat until it stops absorbing, then locked under a clear topcoat. That extra mass is what shrugs off hot tire pickup, the failure that lifts a thin coating at the tire tracks inside two or three summers. Pricing kits? The honest thickness math is in the best garage floor epoxy kits guide. For a garage that lasts, start with solid epoxy and the rest of the coating systems.

Wet to dry: why the can lies by half

Coating is applied wet and lives dry, and the two numbers are not the same. Wet film thickness is how thick the liquid coating is the moment it is rolled down, before any water or solvent flashes off. Dry film thickness is what is left bonded to the slab after it cures. The bridge between them is volume solids, the percentage of the wet coating that stays behind as film.

The formula is simple: dry film thickness equals wet film thickness times volume solids. Roll on a coating at 6 wet mils at 50 percent solids and you keep 3 dry mils. Half left as vapor.

Real numbers make it concrete. Rust-Oleum’s EpoxyShield water-based garage kit runs 52.6 to 52.8 percent volume solids and is applied at 6 to 7 wet mils to leave 3 to 3.5 dry mils per coat, per its technical data sheet. That is why one coat of a box kit gives you a fraction of the floor on the box. A professional high-solids epoxy such as Sherwin-Williams ArmorSeal 1000 HS, whose data sheet is worth reading first, goes on at higher wet mils and loses far less to evaporation. A true 100 percent solids epoxy loses nothing: 20 wet mils cures to 20 dry mils, which is why the thickest builds start there.

How thickness is actually verified

While the coating is still wet, a good installer checks it with a wet film gauge. A wet film gauge is a notched metal comb or wheel pressed straight into the fresh coating; the highest tooth that comes up wet reads the wet mils, and the reading is converted to dry mils using the volume solids on the data sheet. The method is standardized as ASTM D4414, the practice for measuring wet film thickness by notch gages. It costs a few dollars and takes ten seconds, and most residential crews skip it.

Dry film over concrete is harder to check, because the magnetic gauges used on steel do not read on a slab. In practice it is confirmed by coverage math: the data sheet gives square feet per gallon at a target dry film, so spreading a gallon over more area than the sheet allows means you went thinner than spec. Ask for the mixed coverage rate and do the division.

None of this works over a bad slab. Mils bond to profiled concrete, opened by diamond grinding or shot blasting to the surface profile in ICRI Guideline 310.2R, which defines concrete surface profiles CSP 1 through 9. Twenty mils rolled over a smooth, sealed floor is twenty mils that peels in a sheet. The prep step is what the thickness anchors to.

The one sentence to put on your quote

Vague quotes are where thickness quietly disappears. Put this line in writing and hold the bid to it:

“Two-coat 100 percent solids epoxy with a full flake broadcast to refusal, minimum 20 mil dry film thickness, over a slab diamond-ground to ICRI CSP 2 to 3.”

That single sentence pins down the build, the mils, and the prep at once. A contractor who balks at writing a minimum dry film thickness is telling you the number is negotiable, and it is your floor’s lifespan that gets negotiated.

People shop epoxy by brand and finish. I look at one line on the quote: how many mils, dry, and over what profile. Everything else is paint color. A thin coat of the best resin made still fails first.

What people forget about thickness

Thicker is not automatically better. Past a point, extra mils buy diminishing returns and can trap moisture or crack over a slab that flexes. A garage does not need a 60 mil industrial floor. It needs 20 to 30 mil over honest prep. Match the build to the traffic: a spare room takes less than a shop that parks trucks.

The other forgotten piece is cost, and thickness is most of it. As typical national ranges, solid epoxy runs $3 to $7 per square foot and a flake system $5 to $9 per square foot installed, while a DIY kit is $1 to $3 per square foot in materials only, before the prep and labor a real floor is mostly made of. See where the money goes in the per-square-foot breakdown and the full cost pillar, and browse every guide in the Learning Center.

If you already have a quote and cannot find a dry film thickness on it, run your project through the wizard for a local range and the spec questions to ask before you sign.

Frequently asked questions

How thick should an epoxy floor be? For a residential garage, aim for 20 to 30 mil dry film thickness, a two-coat solid or flake build over ground concrete. A low-traffic indoor room can work at 10 to 20 mil. Commercial and industrial floors run 40 to 60 mil and up.

How many mils is a good epoxy floor? A durable professional garage floor is 20 to 30 mil dry. Below about 10 mil you are in DIY-kit territory, which is fine for light use but lifts under hot tires far sooner. Match the mils to the traffic the floor will carry.

How thick is 100 solids epoxy? A 100 percent solids epoxy keeps every wet mil, so what you roll is what you cure: 20 wet mils becomes 20 dry mils with nothing lost to evaporation. That is why the thickest single-coat builds start with 100 percent solids products rather than water-based kits.

Is thicker epoxy better? Up to a point. More mils resist tire pickup, abrasion, and point loads, which is why a garage build beats a DIY coat. Past the traffic the floor actually sees, extra thickness adds cost without benefit and can crack over a flexing slab. Match the build to the use.

How do you measure epoxy thickness? Wet, with a wet film gauge, the notched comb standardized in ASTM D4414, read seconds after the coating goes down. Dry thickness on concrete is confirmed by coverage math from the product data sheet, since magnetic gauges only read on steel.

How this page is maintained

Written and reviewed by Nick Shushan, founder of EpoxyTimes, a flooring contractor with roughly 25 years in the trade, most of it in hardwood in New York, working in epoxy since 2019. Thickness ranges are drawn from manufacturer technical data sheets and standards named inline; system prices come from the site rate card. Last updated September 6, 2026.