How often should I measure the river width?

Every 6 in along the length on most tables, every 4 in on small pieces. More measurements matter most where the edges curve sharply.

Should I measure the width at the top or bottom of the river?

Live edges often slope or undercut, so the river can be wider at the bottom. Measure at the top and bottom at a few points; if they differ a lot, use the average of the two at each point.

Does the depth include the flood coat?

No. Measure the river depth to the top of the slabs. The flood coat is a separate thin layer over the whole top, and the calculator adds it on its own.

How to measure a river table for epoxy

A river table is an irregular shape, which is why single-number estimates go wrong. Measure it this way and your estimate will land within a few percent.

1. Set the slabs in the form first

Measure the river as it will actually be poured: slabs flattened, positioned and clamped in the form, with the gap set to the width you want. Moving a slab later changes the volume.

2. Measure the length of the river

This is the length of the slabs along the river, usually the finished table length before trimming the ends.

3. Measure the width at several points

Mark points along the river every 6 in (every 4 in on a small piece) with chalk. At each point, measure across the river, square to the length. Five to ten measurements give a good average on most tables.

Top view. Measure the river width (w1 to w5) at evenly spaced points, square across the table, and average them. The dashed line is the form.

4. Measure the depth

Depth is from the bottom of the river (the form's base) to the top surface of the slabs. If the slabs are not quite flat, measure at a few spots and use the average.

Cross-section. Depth is measured from the bottom of the river to the top of the slabs; the deep pour goes in as layers, the seal coat lines the edges, and the flood coat covers everything.

5. Add an allowance

Epoxy leaks under the slabs and around the form, stays in cups, and gets planed off. Add 10 to 15 percent. If the edges of the slabs are deeply undercut, or there are knots and cracks that will fill, add more.

Worked example

A 72 in river measured at 6, 8, 5 and 7 in averages 6.5 in. At 1.5 in deep: 72 x 6.5 x 1.5 = 702 cubic inches. Plus 10 percent: 772 cubic inches. Divided by 231: 3.34 gallons of deep pour epoxy, before the seal and flood coats.

Common questions

How often should I measure the river width?: Every 6 in along the length on most tables, every 4 in on small pieces. More measurements matter most where the edges curve sharply.
Should I measure the width at the top or bottom of the river?: Live edges often slope or undercut, so the river can be wider at the bottom. Measure at the top and bottom at a few points; if they differ a lot, use the average of the two at each point.
Does the depth include the flood coat?: No. Measure the river depth to the top of the slabs. The flood coat is a separate thin layer over the whole top, and the calculator adds it on its own.