How to measure your pour
Epoxy is sold and mixed by volume, so an accurate pour starts with an accurate measurement of the space you're actually filling — not the whole workpiece. For a river table, that means measuring the river channel itself: the gap between the two wood slabs, not the overall width of the tabletop. The slabs displace epoxy, so including them in your length-times-width math will badly overstate how much you need.
River channels are rarely a clean rectangle — most taper, curve, or pinch in the middle. Take a few width measurements along the length and use the average rather than the widest point, or you'll overbuy. Depth is usually just the thickness of the slab, measured straight down from the top surface to the base of your mold.
One more thing to plan for before you mix anything: if you're pouring over porous or end-grain wood, do a thin seal coat first. Raw wood off-gasses and can pull air bubbles up through your pour if you skip it — seal coats aren't counted in the volume above since they're a thin, separate pour of their own.
Formula and a worked example
All three pour types in this calculator reduce to the same basic idea — length times width times depth, in inches, gives volume in cubic inches. A round mold uses the circle-area formula instead of length times width. From there, cubic inches convert directly to gallons, liters, or ounces:
Volume (in³) = Length × Width × Depth
Take a river table with a channel 40 in long, averaging 6 in wide, and 1.5 in deep — the same numbers you'd get from measuring a typical live-edge slab pair:
40 × 6 × 1.5 = 360 in³ = 1.56 gallons
Add the standard 10% waste allowance for mixing residue and minor spillage, and the order comes to about 1.71 gallons of mixed epoxy — which this calculator does automatically for any dimensions you enter, along with the liter and fluid-ounce equivalents.
Deep-pour vs. tabletop epoxy
Not all epoxy is rated for the same pour depth, and getting this wrong is one of the most common ways a pour fails. Standard tabletop (casting) epoxycures fast and generates heat quickly in bulk, so it's only rated for thin layers — typically 1/8 to 1/4 in per pour. Deep-pour epoxy is formulated with a slower cure that releases heat gradually, which is what lets it fill thick river channels or molds, usually up to 2 to 4 in per pour.
Pouring past your product's rated max depth traps curing heat in the center of the mass. That heat has to go somewhere — the result is usually overheating, visible cracking, yellowing, or a cloudy, hazy cure instead of a clear one. If your channel or mold is deeper than your epoxy's max rated depth, the fix is to pour in multiple layers, letting each one kick off before adding the next, rather than filling it all at once.
Because max pour depth varies by brand and even by product line within a brand, always check the technical data sheet or label for the specific epoxy you're using rather than assuming a number — this calculator gives you total volume regardless of depth limits, but staying under your product's rated depth is on you.
Why mixed volume matters
Epoxy resin cures through a chemical reaction between two components — resin and hardener — mixed at a specific ratio, most commonly 1:1 or 2:1 by volume. The gallons, liters, and ounces this calculator shows are the total mixed volume: resin plus hardener combined, ready to pour. For a 1:1 system, that means buying (and mixing) half of each component to reach the total.
Mix ratios are calibrated precisely, and eyeballing them is one of the most common causes of a pour that stays tacky or never fully cures. Always measure resin and hardener by volume (or by weight, if your product specifies a weight ratio) using marked mixing cups, rather than estimating by eye — a ratio that's off by even a little can leave soft spots that never harden.
Coverage rule of thumb for flood coats
For a flood coat (the glossy top layer poured over a finished tabletop), coverage depends entirely on how thick you pour it. At the standard 1/8 in flood coat thickness, one mixed gallon covers about:
231 in³ ÷ (144 in² × 0.125 in) ≈ 12.8 sq ft per gallon
That number moves a lot with thickness — a thinner 1/16 in seal coat stretches roughly twice as far, around 25.7 sq ft per gallon, while a thicker 3/16 in coat drops to about 8.6 sq ft per gallon. The "Surface coat" mode above runs this same math for your exact tabletop size and coat thickness, so you don't have to eyeball it against a generic per-gallon figure.