This epoxy calculator works out how much resin a project drinks: enter the surface area and the coat type — seal coat, flood coat, or a deep river-table pour — and get gallons (or liters) to buy, including a waste allowance for mixing cups, drips and the meniscus that climbs every edge. Epoxy is the most expensive liquid in the workshop per ounce, and it cures on its own schedule whether you mixed enough or not, so this is one calculation to do before the hardener goes in.

Surface area –
Resin volume needed –
In liters –
Coverage cross-check –

Volume is pure geometry (1 US gallon = 231 cubic inches). Product yields vary slightly by brand and temperature — resin runs thicker cold and thinner warm — so the 10% waste default is a floor, not a cushion, on big pours.

Epoxy Math Is Volume Math — With Expensive Consequences

There is no mystery in epoxy quantity, only arithmetic: volume = area × thickness, and one US gallon is 231 cubic inches. A square foot at the standard 1/8-inch flood-coat thickness consumes 18 cubic inches, so a gallon covers almost exactly 12.8 sq ft per flood coat — the coverage figure printed on most tabletop-epoxy kits, and the quickest cross-check on any calculator including this one. A seal coat brushed on thin (~1/32 in) sips a quarter of that; a 2-inch river pour drinks sixteen flood coats’ worth in a single lift. The coat selector encodes the standard thicknesses; the custom field exists for everything else — bar tops at 3/16, garage floors at 10–20 mils (enter 0.010–0.020), and layered builds where you sum two coats of different depths by running the calculator twice.

What the pure math can’t see is everything the pour loses on the way: resin clinging to mixing buckets and stir sticks, the torus of material that self-levels over edges and drips onto the floor (taped edges return some of it), the extra depth over low spots in imperfectly flat slabs, and live-edge voids that swallow volume invisibly from above. The 10% waste default is calibrated to a clean rectangular pour; live-edge, bark inclusions, or a first deep pour argue for 15–20%. Running short mid-pour is the expensive failure — a second batch mixed in panic cures with a visible seam line at the interface — while leftover mixed resin is merely a paperweight. Order like it matters, because here it does.

Worked Examples (Verified)

  • 5 ft × 4 ft tabletop, standard 1/8 in flood coat (defaults): 20 sq ft × 18 cu in = 360 cu in = 1.56 gal neat, 1.71 gal with the 10% allowance — buy the 2-gallon kit, not the 1.5. The seal coat the same top needs first: ~0.43 gal at 1/32 in, usually drawn from the same kit.
  • River table, 6 ft × 3 ft river section averaging 10 in wide… measure the void, not the table: a river channel 72 in × 10 in × 2 in deep = 1,440 cu in = 6.2 gal. Deep-pour budgets are channel volumes, and under-measuring the channel’s width variation is the classic river-table shortfall.
  • Garage floor, 20 × 20 ft at 15 mils (0.015 in): 400 sq ft × 144 × 0.015 = 864 cu in ≈ 3.74 gal — before the primer coat; floor systems are priced per kit at stated coverage, and the custom-thickness field speaks their language natively.

Pour Discipline: Where Calculations Succeed or Fail

  • Ratio is sacred. 1:1 and 2:1 systems fail soft and sticky when eyeballed; measure by volume with graduated cups (or by weight only at the manufacturer’s stated ratio), mix a full 3–5 minutes scraping sides and bottom, then transfer to a second cup and mix again — the two-cup method eliminates the unmixed film that causes soft spots.
  • Respect the pour-depth rating. Tabletop epoxy poured deeper than ~1/4 in per lift can exotherm — the curing reaction’s heat feeds itself, smoking, cracking or foaming the pour. Deep work needs deep-pour resin rated for the lift, which is why the coat menu separates them; no calculator result overrides the product’s depth limit.
  • Temperature is a working-time dial. 70–75°F is the sweet spot; every 10°F warmer can halve pot life, colder rooms leave resin honey-thick and full of micro-bubbles that won’t rise out.
  • Seal porous wood first. The seal coat’s real job is blocking the air that wood exhales into your flood coat as bubbles for hours. Skipping it to save 0.4 gallons is how tabletops get craters.
  • Torch or heat-gun bubbles within the first 15 minutes, in quick passes — and re-check at 30 minutes, when late risers arrive from deep grain.
  • Level is a thickness guarantee. On an unlevel surface the resin pools deep on one side; your calculated average thickness becomes 1/16 in on the high corner and 3/16 on the low, with cure and wear behaving accordingly. Shim the piece level before you mix anything.

Cost Notes

Tabletop epoxy typically runs $50–$90 per gallon in kit form (resin + hardener combined volume — note that a “2-gallon kit” of 2:1 means 2 gallons total mixed, a marketing seam worth reading twice). Deep-pour casting resin costs more per gallon and river tables consume it by the bucket; the worked example’s 6.2-gallon channel is a $400–$650 material line before the slabs. Compare kit prices per mixed gallon against this calculator’s output, not per box, and remember pigments, molds (melamine or HDPE forms), and release agents are separate lines that deep pours can’t skip.

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Frequently Asked Questions

How much epoxy do I need for a tabletop?

For the standard build — a thin seal coat plus a 1/8-inch flood coat — plan on about 1 gallon of mixed epoxy per 12.8 sq ft of flood coverage plus roughly a quarter of that again for the seal coat. A 5 × 4 ft top (20 sq ft) needs 1.56 gal for the flood and ~0.43 gal to seal: the 2-gallon kit, with the calculator’s waste allowance included in those figures. Bigger tops scale linearly; only the pour logistics get harder.

How far does 1 gallon of epoxy go?

It depends entirely on thickness, because coverage = 231 in³ ÷ thickness: 1 gallon covers about 51 sq ft at 1/32 in (seal coat), 12.8 sq ft at 1/8 in (flood coat), 6.4 sq ft at 1/4 in, and just 0.8 sq ft at 2-inch casting depth. This inverse relationship is the whole budgeting story of epoxy work — depth is brutally expensive in volume, which is why deep pieces are poured over filler volume (the wood slabs in a river table are doing economic as well as aesthetic work).

What’s the difference between tabletop epoxy and deep-pour epoxy?

Chemistry tuned for heat management. All epoxy curing is exothermic; thin tabletop formulas cure fast and hot, so thick pours of them overheat, crack, yellow or foam. Deep-pour (casting) formulas cure slowly over 48–72+ hours, dissipating heat safely at 2-inch (some rated to 4-inch) lifts, at the cost of patience and usually price per gallon. The calculator’s volumes are identical for both — but never let a volume result talk you into pouring tabletop resin at casting depth.

How thick should an epoxy flood coat be?

One-eighth of an inch is the industry standard for tabletops and bar tops: thick enough to self-level into a glass-flat finish, bury minor surface texture, and provide real wear depth, while staying inside tabletop resins’ per-lift limits. A second flood coat (after a light sand or within the recoat window) builds to 1/4 in for high-wear commercial tops. Thicker single pours of tabletop resin risk exotherm damage; build depth in lifts or switch to a rated deep-pour product.

Why did my epoxy pour come out short?

The four usual thieves: edge runoff (untaped edges shed resin as drips all pour long), low spots in an unlevel or flexible substrate quietly doubling local depth, porous or live-edge wood absorbing and hiding volume from above, and mixing-vessel losses that scale with batch count. The calculator’s waste allowance is your defense, sized up for exactly these: 10% for clean rectangles, 15–20% for live edge, uneven slabs, or many small batches. Measuring the actual piece — not the nominal board size — closes the last gap.

How do I calculate epoxy for a river table?

Measure the channel, not the table: average width of the void (check it in several places — rivers wander), times length, times pour depth, gives channel volume; convert at 231 cu in per gallon. A 72 × 10 in channel at 2 in deep is 1,440 cu in ≈ 6.2 gal, plus the seal coat for both slabs’ inner edges. Use deep-pour resin rated for your lift depth, and consider pouring in two lifts with pigment matched between batches — bought from the same purchase, mixed from the same containers, because batch-to-batch tint variance is real.

Can I use this for epoxy floors?

Yes — enter the floor area and use the custom thickness field with the system’s specified film build in inches (15 mils = 0.015 in, 20 mils = 0.020). A 400 sq ft garage at 15 mils needs about 3.7 gallons of topcoat, plus whatever the primer coat’s stated coverage demands (primers are specified by coverage rate rather than thickness — typically 200–300 sq ft/gal on sealed concrete, half that on porous). Floor kits are sold to a rated coverage; compare the kit’s promise against the calculator’s geometry and distrust any kit claiming dramatically more coverage at the same mil thickness.

Is this epoxy calculator free?

Yes — free, instant, no sign-up. Enter dimensions and coat type for gallons and liters with waste included, plus the per-gallon coverage cross-check.