Epoxy Resin Calculator: River Tables & Pours
Enter the dimensions of the void you’re filling — in inches — and this calculator returns the epoxy you need in fluid ounces, gallons, and liters, splits it into resin and hardener for your kit’s mix ratio, and tells you how many separate pours the job takes at your epoxy’s maximum pour depth. Epoxy is the most expensive liquid in most workshops; this is the tool that keeps you from buying a gallon short or a gallon long.
What the calculator does
Epoxy math fails people twice. First, volume: a “small” river doesn’t look like two and a half gallons, but 60 × 6 × 1.5 inches is exactly that, and under-buying means a visible seam where a new batch met a cured one. Second, depth: every formula has a maximum pour depth — exceed it and the exothermic cure runs away, yellowing, cracking, or literally smoking the pour. The calculator handles both: total volume with a 10% working margin, and the number of sequential pours your chosen epoxy needs to get to full depth safely.
For a river table, measure the river’s width at several points and use the average — rivers taper, and eyeballing the widest point over-buys by a third. For a flood coat on a full tabletop, the “width” is just the table’s width and the depth is typically 1/8–1/4 inch.
The formulas (so you can check the math)
Volume (cu in) = Length × Average width × Depth (all inches)
Fluid ounces = Cubic inches × 0.554 — and per gallon, 231 cu in; per liter, 61 cu in
Buy = Volume × 1.10 (meniscus, drips, and what stays in the mixing cup)
Pours = Depth ÷ max pour depth, rounded up (deep-pour ~2 in; table-top ~1/4 in)
Resin/hardener split = total ÷ (ratio + 1), by volume — a 32-oz job at 1:1 is 16 + 16; at 2:1 it’s ~21 + 11. Always check whether your brand’s ratio is by volume or by weight; they differ because resin and hardener have different densities.
Worked example
A 5-foot river table with a river averaging 6 inches wide, poured 1.5 inches deep in a 2-inch deep-pour epoxy:
Volume = 60 × 6 × 1.5 = 540 cu in → × 1.1 = 594 cu in ≈ 329 fl oz ≈ 2.6 gallons
One pour gets it done (1.5 in < 2 in max), mixed as ~165 oz resin + 165 oz hardener in a 1:1 kit. That’s a real number for a real river table — the projects that look like “a couple of quarts” and cost $250 in resin are exactly why this page exists.
Who this is for
River-table builders first, but the same math covers casting molds, void and knot fills, and flood coats on bar tops and counters. Buying the slab itself is volume math too — the wood CFT calculator and board foot calculator cover the lumber side of the project. And once the epoxy has cured, the wood around it still needs a protective topcoat; the polyurethane vs varnish vs lacquer guide sorts out which film belongs on a table that gets used.
Frequently Asked Questions
How much epoxy do I need for a river table?
Length × average river width × depth, in inches, gives cubic inches; multiply by 0.554 for fluid ounces and add 10%. A typical 5–6 ft river table with a 5–8 inch river runs 2–4 gallons of deep-pour epoxy — budget accordingly before committing to the slab.
Why can’t I pour table-top epoxy 2 inches deep?
Curing epoxy generates heat, and heat accelerates the cure — a feedback loop. Table-top formulas cure fast and hot, safe only in thin layers (~1/4 in). Deep-pour formulas cure slowly and cool, tolerating 2 inches or more. Pour past the rating and the center of the mass can crack, yellow, or boil.
Do I measure the mix ratio by volume or by weight?
Whichever the label says — and they’re not interchangeable. Most hobby kits are 1:1 or 2:1 by volume. If your scale-based instructions give a weight ratio, use that instead; hardener is usually less dense, so the two ratios diverge by several percent — enough to leave a 1:1-by-volume kit sticky if weighed as 1:1.
Does the calculator work for molds and knot fills?
Yes — it’s just volume. For irregular voids, a trick that beats any formula: fill the void with rice or water, pour that into a measuring cup, and you have cubic inches (1 cup ≈ 14.4 cu in). Use the calculator for the regular shapes and the rice trick for the weird ones.