How Much Epoxy for a River Table: Calculating Deep Pours

Quick answer: measure the river's area (its length times its average width), multiply by the slab thickness, and add 15% for resin that soaks into the wood and leaks from the mould. A 60 × 36 inch, 1½ inch thick table with a river covering a quarter of the surface needs about 4 gallons of mixed deep-pour epoxy.

Step 1: Measure the river, not the table

The river is usually irregular. Two practical ways to measure it:

Average width method. Measure the river's width every 6 inches along its length, average those widths, and multiply by the river's length.

Percentage method. Estimate what share of the whole slab the river takes up. A river covering about a quarter of the top is 25%. The epoxy resin calculator has an "area to fill" setting for exactly this.

Step 2: Multiply by depth

For a river table, the pour depth is the full slab thickness. If you're casting a 1½ inch slab, every square inch of river needs 1½ cubic inches of epoxy.

Step 3: Add 15% or more

Deep pours lose more resin than flood coats:

• Live edges and bark absorb resin
• Cracks and knots fill from underneath
• Small leaks in the mould seams are common
• Some resin always stays in the mixing buckets

Use 15% for sealed, well-dried slabs and 20% for porous or cracked wood.

Worked examples

Table	Slab thickness	River share	Mixed epoxy (with 15%)
48 × 24 in coffee table	1 in	30%	about 220 fl oz (1.7 gal, 6.5 L)
60 × 36 in dining table	1½ in	25%	about 516 fl oz (4.0 gal, 15.3 L)
84 × 40 in large dining table	2 in	20%	about 856 fl oz (6.7 gal, 25.3 L)

Working through the dining table

1. Slab volume: 60 × 36 × 1.5 = 3,240 cubic inches
2. River share: 25% = 810 cubic inches
3. Add 15%: 931 cubic inches
4. Convert: 931 × 0.554 = about 516 fl oz, or 4 gallons

Plan each pour separately

Deep-pour epoxies have a maximum pour depth per layer, often somewhere between 1 and 4 inches depending on the product and the room temperature. Pouring deeper than the limit can overheat the resin, causing cracks, bubbles or yellowing.

If your slab is thicker than the limit, divide the total into layers and calculate each separately. Wait the time the manufacturer recommends between layers.

Before you pour

Seal the wood first. A thin seal coat of epoxy over the live edges reduces bubbles and absorption during the main pour. Calculate it separately as a thin coat.

Test the mould. Pour water or check seams with tape before you mix expensive resin.

Buy kit sizes that cover the total. Running short in the middle of a deep pour is hard to fix, so round up to the next kit size.

For tabletop flood coats and smaller projects, see how much epoxy do I need.

Metric example

A 180 × 90 cm slab, 4 cm thick, with a river covering 25% of the surface:

1. Slab volume: 180 × 90 × 4 = 64,800 cm³ (1 cm³ = 1 ml)
2. River: 25% = 16,200 ml
3. Add 15%: about 18,630 ml, or 18.6 litres

Building a mould that doesn't leak

Leaks are the most common reason river tables run short of resin. A good mould:

• Is made of melamine board or another smooth, non-porous sheet
• Has every inside surface covered in sheathing tape or a release film so the resin doesn't stick
• Has every seam sealed with silicone or hot glue on the inside
• Sits level on a stable surface, checked in both directions

Pour a little water or test with a small batch before the main pour if you're unsure.

Calculating with an irregular river

For a river that widens and narrows, measure the width every 6 inches (or 15 cm), add the widths, and divide by the number of measurements to get the average. Multiply by the river's length for the area.

Example: widths of 6, 8, 11, 9 and 6 inches average 8 inches. On a 60 inch river, that's 480 square inches. At 1½ inches thick, the river holds 720 cubic inches, about 399 fl oz before waste.

Planning your purchase

1. Calculate the river pour with 15% to 20% extra.
2. Add a seal coat for the live edges.
3. Add a flood coat over the finished top if you want a glossy surface.
4. Round up to the next kit size.

Common mistakes

Using the slab's length instead of the river's. Rivers often end before the slab does.

Forgetting the wood absorbs resin. Dry, open-grained wood can soak up a surprising amount.

Pouring deeper than the product allows. Split thick slabs into layers.