Where these numbers come from: TotalBoat recommends adding 5-10% for resin lost on the stir stick, in the corners of the mixing cup and to drips. Craft Resin recommends 5-15% and calls a 10% allowance "a good starting point". The MakersMath resin calculator adds 10% by default. Lean to the top of the range on small pours, the bottom on large ones.
The formula
A river table is a channel filled with resin, so the volume is the channel's length times its average width times its thickness:
Length × Average Width × Thickness = Volume in cubic inches
One US gallon is 231 cubic inches, so divide by 231 to get gallons.
Worked example: a 48-inch channel that averages 4 inches wide and is 1.75 inches thick.
- 48 × 4 × 1.75 = 336 cubic inches
- 336 ÷ 231 = 1.45 gallons
- Add 10%: 1.45 × 1.10 = 1.60 gallons
Measuring an irregular river
Live-edge channels are rarely uniform. To get an average width:
- Measure the width at several evenly spaced points along the channel.
- Add the measurements and divide by the number of points.
For example, widths of 2, 4, 6, 3 and 5 inches give (2 + 4 + 6 + 3 + 5) ÷ 5 = 4 inches. Do the same for thickness if the slab thickness varies. For a channel with branches or sharp curves, split it into sections, calculate each one, and add the results.
River table size reference
These figures are computed from the formula above. They are examples of the arithmetic, not product recommendations. Your channel dimensions will differ.
| Length | Average river width | Thickness | Volume | Gallons | Gallons with 10% | |---|---|---|---|---|---| | 36 in | 3 in | 1.5 in | 162 in³ | 0.70 | 0.77 | | 48 in | 4 in | 1.75 in | 336 in³ | 1.45 | 1.60 | | 60 in | 4 in | 1.75 in | 420 in³ | 1.82 | 2.00 | | 72 in | 4 in | 1.75 in | 504 in³ | 2.18 | 2.40 | | 72 in | 6 in | 2 in | 864 in³ | 3.74 | 4.11 |
Planning the purchase
The waste allowance
Buy 10% more mixed resin than the calculation shows, which sits inside the 5-15% range both manufacturers give. A calculation of 2 gallons becomes 2 × 1.10 = 2.2 gallons.
Reading kit sizes
Mixed volume is Part A plus Part B. A kit that holds half a gallon of resin and half a gallon of hardener at a 1:1 ratio makes about 1 gallon mixed. Manufacturers label kits in different ways, some by total contents and some by one component, so check the product page for the mixed volume before you order. For kits with a ratio other than 1:1, such as 2:1, the two parts are not equal, so split the total by the ratio.
Pour depth and layers
Thickness decides which resin you can use, because every product has a maximum depth per pour:
- Craft Resin lists its Deep Pour at 2 inches per layer and its Table Top at 1/8 inch (Craft Resin).
- TotalBoat lists TableTop at 1/8 to 1/4 inch, and its Fathom deep-pour product at 2 inches for river tables (TotalBoat).
If your river is thicker than the product's maximum, pour in layers and follow the manufacturer's recoat window. The total volume is the same either way, so layering changes your schedule, not how much you buy. Use a deep-pour product rated for your depth, and check pot life and cure behavior on its data sheet.
Things that change the volume
- Embedded objects and wood: Subtract the volume of anything that sits inside the channel. Porous or live-edge wood can soak up resin, and Craft Resin suggests allowing more for it. Seal the wood first and treat the 10% allowance as a minimum.
- Pigments and powders: The volume they add is small enough to ignore when planning.
- Mold or channel leaks: A channel that is not fully sealed loses resin. Seal it before you mix.
Common mistakes
- Making the river too shallow. A thin pour looks like a crack rather than a river. Decide your thickness first, then calculate.
- Using one width measurement. Average several points along the channel.
- Forgetting the waste allowance. Mixing cups and stir sticks hold back some resin.
If you run short or have extra
- If you run out mid-pour, mix a small second batch right away. Check your product's data sheet for pot life, since it varies a lot between resins.
- Mixed epoxy cures in the cup, so it cannot be stored. Pour any surplus into small molds straight away, such as coasters, and follow the safety data sheet for disposal.
Key takeaways
- Volume = length × average width × thickness, in cubic inches.
- Divide by 231 for US gallons.
- Add about 10% for waste, within the 5-15% range TotalBoat and Craft Resin give.
- Mixed volume is Part A plus Part B, so check the kit label.
- Match the resin to your depth, since maximum pour depth varies by product.
Ready to run your own numbers? Try our free Resin Calculator. Enter your dimensions and get the amount in seconds.