Film Thickness and Coverage Calculator
Turn solids by volume and a target dry film thickness into real coverage, the wet film to apply, and the volume to order. Runs backward to audit a coat already down.
What Will This Product Actually Cover?
Enter the solids by volume from your data sheet and the dry film thickness you are aiming for. You get the theoretical coverage, the coverage after losses, the wet film to set your gauge to, and the volume to order. Or work it backward: enter a spread rate you measured and see what thickness you really achieved.
What Do You Know?
Work forward from a target thickness, or backward from a spread rate you measured.
Enter the solids by volume percentage and a target thickness to see the result.
How the Film Thickness and Coverage Calculator Works
- Take the solids by volume percentage off the product data sheet. It is not the same as solids by weight
- Enter the dry film thickness the data sheet specifies for your system
- Add the floor area and the number of coats if you want a volume to order
- Set a loss allowance for what stays in the bucket, on the roller, and in the pores of the slab
- Read the wet film figure and set your gauge to it, because that is the only thickness you can control while the coat is wet
- To audit a coat already down, switch to measured spread mode and enter area covered divided by product used
Examples
Frequently Asked Questions
What is the difference between wet film and dry film thickness?
Wet film is how thick the coating is the moment it goes down. Dry film is what is left once the solvent or water has gone and the product has cured. The gap between them is exactly the solids by volume percentage.
At 100% solids nothing evaporates, so the two are the same and the distinction never bites. Below 100% they diverge fast. A 70% solids product laid at 10 mil wet cures to 7 mil dry, so hitting a 10 mil dry spec means applying 14.3 mil wet. Wet film is the only one you can measure and correct while you can still do something about it, which is what a wet film gauge is for.
Where does the coverage number come from?
It is a unit conversion, not an industry estimate. One US gallon is 231 cubic inches. One square foot at one mil thick is 144 square inches times a thousandth of an inch, which is 0.144 cubic inches. Divide and you get 1,604 square feet per gallon at one mil, for a product that is 100% solids.
From there, coverage is 1,604 multiplied by the solids fraction and divided by the target thickness. The metric version is tidier: one litre covers 1,000 square metres at one micron, so coverage in m²/L is 1,000 times the solids fraction divided by the thickness in microns. Nothing in either figure is a judgement call, which is why this calculator can be exact about it in a way it cannot be about a loss allowance.
Why does my real coverage never match the data sheet?
Because the data sheet quotes theoretical coverage, which assumes every drop ends up on the floor at exactly the target thickness. Nothing does.
Product stays in the bucket and on the roller or squeegee. An open, porous or freshly ground slab drinks the first coat. Film pools thicker in low spots than the average implies. Edges, cut ins and changes of direction all take more. A loss allowance is how you account for that, and it is a genuine judgement rather than arithmetic, which is why this tool defaults to 10% and lets you change it. A tight, sealed, previously coated floor may beat that; a rough slab on a first coat will not.
Is solids by volume the same as solids by weight?
No, and using the wrong one produces an answer that is wrong in the expensive direction. Solids by weight is usually the higher number, because the solid part of a coating is typically denser than the liquid part, so a data sheet quoting weight solids will make a product look like it goes further than it does.
Film thickness is a question about volume, so only volume solids predicts it. Data sheets normally list both, labelled. If only one figure is given and it is not labelled, ask the manufacturer rather than assuming.
How much difference does solids content actually make?
More than most quotes assume. Hold the target dry film thickness at 10 mil and vary only the solids: a 100% solids product covers 160.4 ft²/gal, an 80% one covers 128.3, a 60% one covers 96.2, and a 40% one covers 64.2.
So the 40% product needs 2.5 times the material to build the same floor. It is usually cheaper per gallon, and that is the trap: comparing two products on price per gallon without dividing by coverage compares nothing at all. Compare cost per square foot at the same dry film thickness.
What does the measured spread mode do?
It runs the arithmetic backward, so you can audit a coat instead of planning one. Divide the area you covered by the product you actually used, enter that as your spread rate, and it returns the dry film thickness that rate produces.
It is the fastest way to find out whether a floor got the specification it was quoted for, and it is worth doing on the first bay rather than at the end. A crew running 200 ft²/gal on a 100% solids product is laying 8 mil, and if the spec said 10 the floor is 20% thin before anyone has noticed.
Important Notes
- Solids by volume, not solids by weight. They are different numbers and only the volume one predicts film thickness
- The 1,604 constant is a unit conversion, not an estimate: 231 cubic inches per gallon divided by 0.144 cubic inches per square foot per mil
- The 10% default loss allowance is a common starting point, not a measured figure. Set it from your own experience of the floor in front of you
- Theoretical coverage is what a data sheet quotes. Ordering against it without a loss allowance is how jobs run short
- A wet film gauge is the only way to control thickness while the coat is still wet. Check early and check often
- Always confirm the target thickness against your product data sheet, because the same generic system can be specified very differently by two manufacturers