River Table Epoxy Calculator — Volume Math & Layer Schedule

Quick answer

River table gallons = channel volume ÷ 231. Measure the channel — not the slab — in inches: a 6 ft × 8" × 1.5" river is 72 × 8 × 1.5 = 864 in³ ÷ 231 = 3.74 gallons, ×1.10 waste = 4.1 gal → one 6-gal kit. Pour it in layers at the brand's cap (1.5–2" for most deep pours), waiting out each recoat window. The calculator below opens in deep-pour mode — length, width, depth, done.

The volume math is the honest math

Coverage charts describe films; river tables are casts. The 231 in³/gal conversion is exact — and it self-validates against the brands' own published examples: Primaloc says a 1.5-gal kit covers 10 sq ft at 1/4" (10 × 0.25 ÷ 1.604 = 1.56 gal ✓); Upstart's official calculator runs 231 in³/gal on a 96×48 example. When your channel is an irregular live-edge shape, compute the bounding box of the river only — wood displaces epoxy, so the slab's mass is your ally, not part of the pour.

Layer schedules from the datasheets

Two patterns worth noticing: every brand's added-layer cap is lower than its first-layer cap (heat accumulates downward), and the 2:1 deep pours all breathe slower than the 1:1 systems — their recoat windows are measured in a day, not hours. Plan the weekend accordingly: a 2"-deep 6 ft river is two or three pours across two or three days.

The exotherm rules that keep the cure alive

• Mass, not just depth. Fathom caps small-mold pours at 1 gallon mixed volume even where depth allows 3" — the heat scales with volume.
• Cool between layers. Fathom's window assumes the layer dropped below 85 °F; pouring warm-on-warm stacks exotherms.
• Never tabletop resin in a river. 1/8–1/4" products poured 2" deep are the classic cracked-and-ambered beginner slab.
• Gel-stage step pours (Stone Coat's 8" technique) are advanced: the prior layer must be firm-but-tacky at exactly the right window, or you trap uncured resin — read their page before trying it, not after.

After the volume math

The final surface usually still wants a thin flood of tabletop resin for glass-gloss — a 1/8" coat on the slab's top at your tabletop brand's rate from the coverage calculator. Deep pour cures flatter but not glossier. And the mix ratio calculator splits every layer's 2:1 batch exactly — mixing a 2.5-gal layer by eye is how deep pours die. Kit economics are worth checking before you commit: the same river priced across brands can vary by half the job's cost, which the cost calculator shows, and the brand pages carry each deep pour's layer caps with their sources.

A worked schedule, end to end

Take the 6 ft × 8" × 1.5" channel that needs 3.74 gallons of mixed epoxy. With TotalBoat Fathom (2:1, dual-verified TDS) that is two layers of ~1.87 gallons each — each batch splits at 2:1 into 1.25 gal resin + 0.62 gal hardener. The channel's depth (1.5") is inside Fathom's 3" small-mold cap but sits above its 2" river-slab guidance, so two layers at 24–36 hours apart is the conservative schedule the TDS itself prefers over one hot 3.7-gallon mass. Day three: demold check, then the tabletop flood coat for gloss. Total kit buy: one 6-gallon Fathom kit at $449.99 — or two 3-gal kits at $229.99 each, $10 more for schedule flexibility.