How Much Epoxy Do You Need for a River Table?

Updated 2026-10-16

Running out of epoxy halfway through a river pour is one of the most stressful things that can happen in a woodworking shop. Ordering far too much is the opposite problem: deep pour epoxy is one of the most expensive materials in a river table. The good news is that the amount you need is a straightforward geometry problem. This guide walks through the measurement and math step by step, explains where the "hidden" epoxy goes, and shows how to turn the result into a shopping list.

If you just want the number, use the river table epoxy calculator. If you want to understand it (and double-check it), read on.

The basic formula

A river table's epoxy is the volume of the empty space between your slabs inside the form. Since the river has wavy edges, you approximate it as a fraction of the whole tabletop:

The number 231 is not an approximation — a US liquid gallon is defined as exactly 231 cubic inches. For fluid ounces divide cubic inches by about 1.8047, and for liters multiply cubic inches by 0.016387.

Step 1: Measure the finished table size

Measure the length and width of the table as it will be cut, which is usually the inside dimensions of your form. Use inches throughout to keep the arithmetic simple. If you work in centimeters, that's fine too — just stay consistent and convert at the end (1 liter = 1,000 cm³).

Step 2: Decide the pour depth

The pour depth is normally the full thickness of your slabs, because the river must fill the gap from the bottom of the form to the top surface. Many people pour slightly proud of the wood and flatten it afterwards; if you plan to do that, add that extra thickness to the depth. If your slabs vary in thickness, use the thickest point — epoxy fills to the highest level you need.

Step 3: Estimate the river percentage

This is the step where most estimates go wrong, because live edges are irregular. A reliable method:

1. Lay the slabs in their final position in the form.
2. Measure the river's width at evenly spaced points along the length — every 6 inches is a good interval for a typical dining table; use more points if the edges are very wavy.
3. Add up the widths and divide by the number of measurements to get the average river width.
4. Divide the average river width by the table width.

For example, if your measurements average 9 inches on a 36-inch-wide table, the river covers 9 ÷ 36 = 0.25, or 25% of the surface.

An alternative is to photograph the layout from directly above, trace the river on graph paper or in an image editor, and count squares or pixels. Either way, you are estimating area — the more points you sample, the better the estimate.

Step 4: Do the math (worked example)

Suppose your table is 72 inches long, 36 inches wide and 1.5 inches thick, with a river covering 25% of the area.

• Full table volume: 72 × 36 × 1.5 = 3,888 in³
• River volume: 3,888 × 0.25 = 972 in³
• Gallons: 972 ÷ 231 ≈ 4.21 gallons
• Fluid ounces: 972 ÷ 1.8047 ≈ 539 fl oz
• Liters: 972 × 0.016387 ≈ 15.9 L

That 4.21 gallons is the theoretical volume of the gap. You will need more than that, for reasons explained next.

Step 5: Add an allowance for "hidden" epoxy

Several things consume epoxy that the simple formula doesn't capture:

• Cracks, knots and voids. Live-edge slabs often have checks and soft areas that soak up epoxy. Bark that's left on can trap pockets that fill later.
• Leaks. Even a well-sealed form can weep at corners. Sealing seams carefully and testing the form helps, but it's wise to assume some loss.
• Mixing containers. A thin film of resin stays on every bucket and stir stick.
• Seal coats. Many woodworkers brush a thin seal coat on the live edges before the main pour to limit air release from the wood. That is extra epoxy, though usually a small amount.
• Top-up pours. As epoxy soaks into the wood and settles, the level can drop slightly, and a final top-up may be needed.

A 10–20% buffer is a common rule of thumb. Use the lower end for well-sealed forms and stable, crack-free slabs, and the upper end for slabs with lots of checks or bark. In the example, 4.21 gallons plus 15% is about 4.84 gallons.

Step 6: Check your product's maximum pour depth

Epoxy releases heat as it cures. In a thick mass that heat builds up, which is why deep pour (casting) epoxies exist and why each one lists a maximum thickness per pour. If your river is 1.5 inches deep and your epoxy is rated for 1 inch per pour, you need two layers. The total volume doesn't change, but you'll mix it in batches. Our deep pour calculator splits the volume per layer, and our guide on deep pour vs tabletop epoxy explains the difference.

Step 7: Plan the mix ratio

Most river table epoxies are two-part systems, with ratios such as 1:1 or 2:1 (resin to hardener). For a 2:1 by volume system and a 5-gallon total, you'd measure about 3.33 gallons of resin and 1.67 gallons of hardener. Be careful: some products specify the ratio by weight, and because the two parts have different densities, the volume ratio and weight ratio aren't interchangeable. Always follow the label.

Don't forget the top coat

After the river is cured and the table is flattened and sanded, many makers finish with a thin flood coat of tabletop epoxy, or with an oil or other finish instead. If you choose an epoxy flood coat over the whole surface, calculate it separately with the tabletop coating calculator: at 1/8 inch thick, each square foot needs about 18 cubic inches (roughly 10 fl oz). For the 72 × 36 inch table (18 sq ft), that's 324 in³, or about 1.4 gallons before waste.

Turning volume into a shopping list

Epoxy is sold in kits that combine both parts, often labeled by total volume. When you compare kit sizes, check whether the size on the label refers to the combined kit or to one part only. Then round up to the next kit size that covers your total including the buffer. Leftover sealed epoxy may keep for a while, but shelf life varies by product, so check the manufacturer's storage guidance.

Common mistakes

• Mixing units. Entering length in feet and depth in inches gives a result off by a factor of 12 or 144. Convert everything to one unit first.
• Using nominal thickness. A slab sold as "2 inch" may be thinner after flattening. Measure what you actually have.
• Ignoring the gap under the slabs. If slabs are raised on spacers, epoxy will flow underneath them too. Either seal the slabs to the form or include that thin layer in your calculation.
• Forgetting temperature. Cold epoxy is thicker and harder to mix and pour; warm epoxy cures faster and hotter. Follow the temperature range on the data sheet.

Quick reference

For a quick sanity check, here is the theoretical river volume (no buffer) for a 1.5-inch-thick table at different sizes and river percentages, calculated with the formula above:

Summary

To find how much epoxy your river table needs: multiply length × width × depth in inches, multiply by the river's share of the area, divide by 231 for gallons, and add 10–20% for waste. Check the maximum pour depth to decide how many layers you'll pour, and calculate any flood coat separately. Plug your numbers into the river table epoxy calculator to get gallons, ounces, liters, weight and part A/B amounts in one step.