Epoxy Resin Calculator

Epoxy resin isn't forgiving when you get the amount wrong. Pour too little and you're left staring at a thin spot right in the middle of your countertop—with a half-cured batch and no way to fix it cleanly. Buy too much and you've got $60 worth of resin hardening in a bucket.

This epoxy resin calculator tells you exactly how much you need before you open a single container. Enter your project dimensions and get results in gallons and fluid ounces—for surface coatings, deep pours, or both.

The calculator is split into two sections. The surface mode is for coating projects like bar tops, countertops, and table finishes where you're spreading a thin layer over a flat area. The volume mode is for casting and filling projects—river tables, molds, embedments—where you're pouring resin into a space with depth. If your project needs both (like a river table that also gets a topcoat), use both sections and add the totals together.

For surface coatings (bar tops, countertops, table finishes):

1. Measure your surface length and width in feet
2. Enter both values in the Surface Dimensions section
3. Read your results — total square footage and gallons needed for coating

For volume fills (river tables, molds, casting projects):

1. Measure the length, width, and depth of your fill area in inches
2. Enter all three values in the Volume Dimensions section
3. Read your results — fluid ounces and gallons needed

One thing to note: if your project involves a seal coat and a volume fill and a surface flood coat, you'll want to calculate each step separately and add them up. A river table, for example, typically needs a seal coat on the raw wood, the deep pour to fill the channel, and then a final flood coat over the entire surface.

The general rule you'll see everywhere is that one gallon covers about 12 square feet at 1/8-inch thickness. That's a decent starting point, but the real number depends heavily on what you're pouring over and how thick you're going.

Here's what coverage actually looks like across different project types:

There's a catch that trips up a lot of first-timers: porous surfaces absorb epoxy. Your first seal coat on raw wood will look like it practically disappeared after 10 minutes—the wood just drinks it in. This is normal. That first coat is essentially sacrificial; it fills the pores so your flood coat actually stays on the surface where you want it. End grain is even worse—expect it to absorb two to three times more than face grain on the same piece of wood.

Most table top and countertop projects need at least two coats: a thin seal coat followed by a thicker flood coat. Budget for both from the start.

This trips up more beginners than almost anything else. These aren't just two different thicknesses of the same product—they're fundamentally different formulas, and using the wrong one will ruin your project.

Coating epoxy (table top epoxy) is engineered for thin applications, usually 1/8 inch or less per layer. It self-levels into a smooth, glass-like surface and cures within 24–72 hours. This is what you use for bar tops, countertop finishes, and tabletop coatings.

Casting epoxy (deep pour resin) is designed for thicker pours—typically 1 to 2 inches per layer, with some specialty products handling up to 4 inches. It generates less heat during curing, which is critical at depth.

Here's why you can't cheat this: epoxy cures through an exothermic chemical reaction. The thicker the layer, the more heat builds up. Pour table top epoxy 2 inches deep and the heat can spike high enough to cause cracking, yellowing, or warping. Casting epoxy avoids this by curing more slowly, giving the heat time to dissipate.

Bottom line: match the epoxy type to your pour depth. The calculator gives you the volume—you pick the right product for the job.

The math is simple, but converting between units by hand gets old fast.

Surface coating:

Surface Area = Length (ft) × Width (ft)

Gallons Needed = Surface Area ÷ 20

This calculator uses 20 square feet per gallon, which reflects a standard thin coating or seal coat application.

Volume fill:

Volume = Length (in) × Width (in) × Depth (in)

To convert cubic inches to gallons: divide by 231 (there are 231 cubic inches per US gallon).

To convert to fluid ounces: multiply gallons by 128.

Worked example: A mold that's 20″ × 20″ × 2″ = 800 cubic inches. Divided by 231 = 3.46 gallons. That's roughly 443 fluid ounces of mixed epoxy.

Before you measure anything, here's a rough sense of what common projects require:

These are estimates for the resin itself. Always add 10–15% for waste—more on that below.

Rectangles are easy. Live-edge slabs, river table channels, and freeform molds are not.

For river tables and live-edge pieces: Measure the width of the channel (the void between the two slabs) at several points along the length. Average those measurements and use that as your width. Then multiply by the length and depth as usual. Add 15–20% on top since the irregular edges will create pockets you can't perfectly account for.

For round or oval shapes: Measure the diameter, divide by 2 to get the radius, and use the formula: Area = π × radius². For volume, multiply by the depth.

The water trick for truly irregular shapes: If your mold or void is too complex to measure—like a burl slab with deep crevices—line it with plastic sheeting, fill it with water, then pour the water into a measuring container. That tells you the exact volume you need. Just make sure the mold is completely dry before you pour any resin.

Your calculator result is accurate for the geometry you entered. But real projects have variables that math alone can't capture.

Surface porosity. Unsealed wood absorbs 15–30% more epoxy than the calculation suggests. End grain, knots, and bark inclusions are particularly thirsty. Always apply a seal coat first.

Temperature. Warmer shops (75–85°F) make epoxy thinner and more self-leveling—it spreads further. Cooler conditions (below 65°F) thicken it and reduce coverage. Most manufacturers recommend working between 70–80°F.

Mixing waste. You'll lose 1–2 ounces per batch to the walls and bottom of your mixing container. On small pours, that adds up fast. On a batch measured in gallons, it's negligible.

Edge drips. Epoxy flows. On surface coats, it will drip off every edge. Some people collect and reapply the drips during the first 15–20 minutes; others accept it as waste.

Multiple coats. A standard countertop project typically looks like this: one seal coat (thin), one to two flood coats (1/8″ each), with light sanding between layers. Calculate for all coats, not just the first.

How much extra to buy by project type:

Running short mid-project is significantly worse than having a bit left over. Epoxy doesn't go bad in sealed containers—save it for your next project.

Skipping the seal coat. This is the most common reason people run short on their flood coat. The wood absorbs resin from your main pour, leaving you with thin coverage and no time to mix more before it starts curing.

Mixing more than you can use. Table top epoxy typically gives you 20–45 minutes of working time after mixing. If you can't spread it all in that window, it starts gelling in the bucket. Mix in smaller batches if you're covering a large area.

Eyeballing dimensions. Rounding "about 7 feet" up to 8 feet doesn't sound like much, but it can mean buying a full extra gallon. Measure with a tape measure, not guesses.

Not leveling the work surface. If your table or mold isn't perfectly level, epoxy pools on the low side and leaves the high side thin. Check with a bubble level and shim before you pour.

Confusing kit volume with resin volume. Epoxy is sold as a two-part system (resin + hardener). A "1-gallon kit" gives you 1 gallon of mixed material total—typically a half-gallon of each part. You're not getting 2 gallons. Read the label carefully when purchasing.