Epoxy Calculator: How Much Epoxy Resin Do You Need?

Running out of epoxy halfway through a pour is every resin crafter's nightmare. Once you mix that resin and hardener together, you've got a limited window before it starts curing — and there's no pause button. Ordering too little means a ruined project. Ordering too much means wasted money sitting on your shelf.

This epoxy calculator helps you nail the right amount before you order. It handles two types of projects: surface coatings (like a countertop flood coat) and deep pours (like filling the channel in a river table). Plug in your dimensions, and it instantly tells you how many gallons you need.

No guessing. No math on the back of a napkin. Just accurate numbers so you can order the right amount of resin for your project.

Before you start punching in numbers, it helps to know which section of the calculator to use. The difference comes down to one question: are you coating a flat surface, or filling a space?

This is for any project where you're spreading a thin, even layer of epoxy across a surface. Think:

• Countertops and bar tops — that smooth, glass-like finish
• Table tops — protecting and sealing wood
• Garage and basement floors — durable, easy-to-clean coating
• Seal coats — the thin first layer that locks in air bubbles before a flood coat

Surface coats are measured in square feet because you're really just covering area. The standard flood coat is about 1/8-inch thick, and at that thickness, one gallon covers roughly 20 square feet.

This is for any project where epoxy needs to fill a space with real depth:

• River tables — filling that winding channel between live-edge slabs
• Casting molds — embedding objects like bottle caps, coins, or flowers
• Knot and void fills — patching holes, cracks, and bark pockets in wood
• Thick resin art — layered or 3D pieces with noticeable depth

Deep pours are measured in cubic inches because depth changes everything. A 2-inch river channel uses roughly 16 times more epoxy than a 1/8-inch surface coat over the same footprint. That's not a rounding error — that's the difference between a $40 order and a $300 one.

Not sure which to pick? If your epoxy layer is 1/4 inch or thinner, use the surface section. If it's thicker than 1/4 inch, use the volume section.

You don't need to do any of this by hand — the calculator handles it — but understanding the formulas helps you sanity-check results and plan for irregular shapes.

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

Gallons Needed = Surface Area ÷ 20

That "20" is the standard coverage rate: one gallon of mixed epoxy covers about 20 square feet at 1/8-inch thickness. Planning a thicker flood coat? Halve the coverage. At 1/4 inch, a gallon only covers about 10 square feet.

Volume (cubic inches) = Length (in) x Width (in) x Depth (in)

Fluid Ounces Needed = Volume ÷ 1.805

Gallons Needed = Volume ÷ 231

Where do those numbers come from? One fluid ounce equals 1.805 cubic inches, and one gallon equals 231 cubic inches. So if your river channel is 576 cubic inches, that's about 319 fluid ounces, or roughly 2.5 gallons of mixed resin.

Got a round table top? Calculate as if it's a square (diameter x diameter), then multiply by 0.785 to get the circular area. For L-shaped countertops, break the shape into two rectangles, calculate each separately, and add them together.

1. Measure your surface in feet. For countertops, measure the longest straight edge and the depth from wall to front. If your surface wraps around a corner, measure each straight section separately.
2. Enter length and width in the Surface Dimensions section.
3. Check your results below — you'll see total square footage and gallons needed for a standard 1/8-inch flood coat.

Pro tip: If you're planning a seal coat plus a flood coat (which is the right move for most wood surfaces), multiply your gallon result by about 1.5 to cover both layers.

1. Measure your void in inches. For a river table, measure the channel at its longest point, widest point, and deepest point. If the channel varies in width, use the average width.
2. Enter length, width, and depth in the Volume Dimensions section.
3. Check your results — you'll get fluid ounces and gallons. Fluid ounces are handy for smaller projects where you're buying by the bottle rather than the gallon.

Pro tip: River table channels are almost never perfectly rectangular. The live edges curve, bark voids create pockets, and the bottom isn't always flat. Add 15-20% to your calculated amount to account for these irregularities.

These are approximate averages. Your specific product may differ — always check the manufacturer's technical data sheet for their recommended coverage rates.

An L-shaped kitchen counter: one section is 8 ft x 2.5 ft, the other is 4 ft x 2.5 ft.

• Total surface area: (8 x 2.5) + (4 x 2.5) = 30 sq ft
• Seal coat: 30 ÷ 40 = 0.75 gallons
• Flood coat: 30 ÷ 20 = 1.5 gallons
• Total for both coats: ~2.25 gallons
• Order recommendation: 2.5 to 3 gallons (accounts for edge drip-off, mixing waste, and any touch-ups)

The river channel measures 60 inches long, averages 10 inches wide, and you want a 1.5-inch deep pour.

• Channel volume: 60 x 10 x 1.5 = 900 cubic inches
• Gallons: 900 ÷ 231 = 3.9 gallons
• Plus a surface flood coat on the whole 60" x 30" table top: (5 ft x 2.5 ft) = 12.5 sq ft ÷ 20 = 0.625 gallons
• Total project: ~4.5 gallons
• Order recommendation: 5 to 5.5 gallons. River channels always have more volume than a perfect rectangle because of the curved live edges and bark pockets.

Garage is 20 ft x 22 ft with a standard two-coat system.

• Surface area: 20 x 22 = 440 sq ft
• Primer coat: 440 ÷ 40 = 11 gallons
• Topcoat: 440 ÷ 20 = 22 gallons
• Total: ~33 gallons
• Order recommendation: 36-38 gallons. Concrete absorbs epoxy, and older, more porous garage floors can soak up significantly more on the primer coat. Better to have a few extra gallons than end up with thin, patchy coverage in the corners.

A 14-inch diameter round serving tray mold, 3/8 inch deep.

• Square equivalent: 14 x 14 x 0.375 = 73.5 cubic inches
• Circle adjustment: 73.5 x 0.785 = 57.7 cubic inches
• Fluid ounces: 57.7 ÷ 1.805 = 32 fl oz (about 1 quart)
• Order recommendation: 40 fl oz. Resin art often needs a bit more than calculated because you'll want enough to torch out bubbles, spread evenly, and not worry about running thin at the edges.

You're embedding pennies in a 6 ft x 2 ft bar top with a 1/4-inch epoxy flood over the top.

• Surface area: 6 x 2 = 12 sq ft
• Gallons at 1/4" thickness: 12 ÷ 10 = 1.2 gallons
• Order recommendation: 1.5 gallons. The pennies displace some volume (saving you a little epoxy), but the gaps between them create tiny channels that need to be completely filled. These roughly cancel out, so just add the usual 10-15% margin.

Confusing "kit size" with "mixed volume." A "1.5-gallon kit" with a 2:1 mix ratio contains 1 gallon of resin and 0.5 gallons of hardener. You get 1.5 gallons of mixed epoxy total — not 1.5 gallons of resin plus additional hardener. Read the label carefully. Some brands advertise kit size, others advertise mixed yield. That misunderstanding alone can leave you a gallon short on a big project.

Using table top epoxy for a deep pour. Table top (coating) epoxy and deep pour epoxy are different formulas. Table top epoxy is designed for thin layers and cures fast. If you pour it 2 inches deep, the heat from the curing reaction can crack it, yellow it, or in extreme cases cause it to smoke. Always match the epoxy type to your pour depth.

Forgetting to account for the seal coat. Almost every wood project needs a thin seal coat before the main flood coat. This layer soaks into the grain and seals air pockets, preventing bubbles from rising up through your final coat. If you only calculate enough for the flood coat, you'll come up short.

Measuring feet when you meant inches (or vice versa). The surface section of this calculator uses feet. The volume section uses inches. Mixing these up gives you wildly wrong results. A 20-foot measurement entered as 20 inches would underestimate by a factor of 12.

Skipping the waste factor. Epoxy coats the inside of your mixing bucket, sticks to your stir stick and spreader, drips off edges, and fills micro-cracks you didn't know existed. Always add 10-15% beyond your calculated amount.

Round up, not down. If the calculator says 2.3 gallons, buy 3 gallons. You can always use leftover resin for a small project, coasters, or test pours. You can never un-ruin a pour that ran short.

Measure at multiple points. River table channels aren't uniform. Measure the width at 3-4 spots along the length and use the average. Same with depth — check the deepest and shallowest points and split the difference.

Do a dry test with water. For complex shapes where math alone isn't reliable (like a heavily curved river channel or an irregular mold), fill the space with water, then pour the water into a measuring cup. That's your volume. Just make sure the surface is completely dry before working with epoxy.

Plan your pours in layers for deep projects. Most deep pour epoxies max out around 1 to 2 inches per layer (check your product's specs). If your channel is 3 inches deep, that's two separate pours with 24-48 hours of cure time between them. Factor that into both your timeline and your epoxy budget — you'll need separate batches mixed fresh for each pour.

Keep extra on hand for touch-ups. Even a perfect pour sometimes needs a small touch-up where air bubbles left craters or an edge didn't flow all the way to the corner. Having 4-8 extra ounces of mixed epoxy gives you a safety net without a big added cost.

Check your work area temperature. Ideal conditions for most epoxies are between 70-80°F. Below 65°F, epoxy gets noticeably thicker and won't self-level as well, which can cause uneven coverage. Above 85°F, it cures faster, giving you less working time. Neither changes how much you need by much, but it absolutely affects how well it spreads.