How much epoxy do you need for a river table?

The amount of resin a river table needs is a volume problem with one awkward input: the width of a river whose edges are never straight. Get that width right and the rest is arithmetic. This guide walks through the measurements, the allowances manufacturers themselves build in, and the checks to make before you order.

Step 1: measure the river, not the slab

You need three numbers, all measured inside the form:

Length of the river from one end of the form to the other.
Average width of the gap between the slabs.
Thickness of resin, from the form base to the finished resin surface. On a river table this is usually the slab thickness.

The width is where estimates go wrong. A live edge wanders, so the widest and narrowest points tell you little. Lay the slabs in the form in their final position and measure the gap every 10 to 12 in along its length. Average those numbers. The 10–12 in spacing is our suggestion, not a manufacturer figure; EcoPoxy’s river table tutorial likewise works from the average gap between the slabs as the width (EcoPoxy).

Step 2: calculate the volume

V = L × W_avg × T

In inches, the result is in cubic inches. Divide by 231 to get US gallons, since one gallon is defined as exactly 231 in³ (NIST Handbook 44, Appendix C). In centimetres, the result is in cm³, which is the same as millilitres; divide by 1,000 for litres.

The river table calculator does this and accepts a list of width measurements directly.

Step 3: add allowances, and know which ones you are adding

Two different things make a real pour use more resin than the geometry says:

Voids in the wood. Cracks, bark pockets and undercut live edges fill with resin. EcoPoxy’s own volume calculator adds 5 % to the calculated volume for resin that may fill voids and cracks in the wood during the pour (EcoPoxy).
Mixing loss. Resin stays on bucket walls and stir sticks. How much depends on your containers and batch sizes, not on the wood.

Keep the two separate. A slab with clean, sealed edges needs little void allowance, but you will still leave resin in the bucket.

A check against a manufacturer’s own example

EcoPoxy’s tutorial gives a worked case: an average gap of 5.5 in, a length of 50 in and a depth of 3 in, for which its calculator returned 3.75 gal (14.2 L) (EcoPoxy).

The geometry alone is 50 × 5.5 × 3 = 825 in³, or 3.57 gal. Add EcoPoxy’s 5 % and you get 3.75 gal, exactly their figure. The tutorial then rounds up and says 15 L of resin was used. That is a useful sanity check: the manufacturer’s number is plain geometry plus a stated allowance, and the builder still bought a margin on top.

Step 4: seal the wood first, and count that resin separately

Wood releases air as resin surrounds it. EcoPoxy recommends seal-coating every surface that will be submerged in its casting resin, because air and moisture escaping from the wood can cause bubbles (EcoPoxy). TotalBoat likewise says the wood needs to be sealed before the main pour, and notes that not every deep-pour epoxy is suited to sealing (TotalBoat).

The seal coat is a thin film brushed onto the live edges and the underside of the slabs, often with a different, faster product. Estimate it with the flood coat calculator using the area of the surfaces you will seal and a thin coat thickness.

Step 5: build a form that holds every drop

A leak loses resin you paid for and can drain a layer before it cures. Manufacturer guidance is consistent here:

EcoPoxy recommends mold sides at least 1/2 in taller than the slab thickness to avoid overflow, sealing tape on the mold pieces, and a bead of silicone in the inside corners, which it finds easier and more leak-proof than taping the edges (EcoPoxy).
The same tutorial asks for a level, leak-proof form and suggests a polyethylene sheet under the mold to catch any leak (EcoPoxy).
TotalBoat’s river table kit advice is to line the box with plastic tape and run silicone or marine sealant along all seams and joints (TotalBoat).

Measure the form’s inside dimensions after it is built. If the form is wider than the river at the ends, that space fills too and belongs in your length × width.

Step 6: check the layer limit before you buy

Deep-pour resins have a maximum thickness per pour. A 2 in slab may be one pour with one product and two to four with another (the product database lists limits from 1/2 in to several inches), and each extra pour adds the published wait between pours, often around a day, to the build. Enter your thickness in the layer planner with the product you are considering; it reads the limit from the product’s data sheet.

Step 7: convert to kits

Resin kits are usually sized by the mixed volume of Part A plus Part B. Divide your total by the kit size and round up. The cost estimator shows how many kits to buy and how much will be left over at the price you enter.

Quick reference

Measurement	How to get it
Length	Inside the form, end to end
Average width	Gap measured every 10–12 in, averaged
Thickness	Form base to finished resin surface
Void allowance	Small for clean, sealed edges; more for cracks and bark pockets
Mixing loss	Your own figure, based on bucket size and number of batches