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.
This guide covers the question a volume number cannot answer on its own: how deep can one pour be, and how does that split a thick project into layers? For unit conversions and basic formulas see the epoxy resin volume calculator guide; for choosing the waste percentage see the resin waste buffer guide.
Check the Pour Depth Limit First
Each epoxy has a maximum thickness per layer. Pouring thicker than the rating generates more heat than the product is designed for. TotalBoat warns that going beyond its recommended depth can cause yellowing, cloudiness, cracking and improper cure, and its calculator page tells you not to dispense more than the manufacturer's maximum recommended amount.
Examples from manufacturer pages (always confirm on the data sheet for your exact product and volume):
| Product type | Maximum per layer | Source | |--------------|-------------------|--------| | Craft Resin Table Top Resin | 1/8 in (3 mm) | Craft Resin | | Craft Resin Arts & Crafts Resin | 1/4 in (6 mm) | Craft Resin | | Craft Resin Deep Pour Resin | 2 in (5 cm) | Craft Resin | | TotalBoat TableTop Epoxy | 1/8 in to 1/4 in | TotalBoat | | TotalBoat Fathom deep pour | 2 in for river tables and slab pours; 3 in for castings under one gallon | TotalBoat |
If your project is deeper than the rating, either pour in layers or use a deeper-rated product. Craft Resin says the same. The wait between layers is product-specific: TotalBoat's calculator page says to apply the next stage once the previous pour has started to harden and cool, while its Fathom page gives a longer wait for step pours. Follow the data sheet.
Volume per Layer
Volume is area × thickness, so a layer's resin is the channel's area times that layer's depth. For the 24 × 48 in table below (a 4 in wide, 48 in long channel, so 192 sq in of area), here is how many layers each rating means for a 2 in deep channel:
| Product rating | Layers for 2 in | Volume per layer | With 10% allowance | |----------------|-----------------|------------------|---------------------| | 1/8 in | 16 | 24 in³ (13.3 fl oz) | 26.4 in³ (14.6 fl oz) | | 1/4 in | 8 | 48 in³ (26.6 fl oz) | 52.8 in³ (29.3 fl oz) | | 2 in | 1 | 384 in³ (212.8 fl oz) | 422.4 in³ (234.1 fl oz) |
The total resin is the same in each case (384 cubic inches before waste). Layers change when you pour, not how much you need. Work out the allowance per mix, because each mix leaves its own residue on the cup and stick.
Worked Example: River Table (24 × 48 in)
A 48 in long river channel, 4 in wide on average, filled to a 2 in slab thickness.
- Channel volume: 4 × 48 × 2 = 384 cubic inches
- Add the 10% allowance: 384 × 1.10 = 422.4 cubic inches
- To gallons: 422.4 ÷ 231 = 1.83 gallons (234.1 fl oz)
Buy 2 gallons of mixed resin (for example a kit that makes 2 gallons once Part A and B are combined). If you are pouring in 1 in layers instead, each layer is 192 cubic inches before waste, or 211.2 cubic inches with 10% (117 fl oz).
For a 3 in thick channel at the same size, it is 4 × 48 × 3 = 576 cubic inches, 633.6 with 10%, which is 2.74 gallons (351 fl oz).
Other Worked Examples
Coaster set (6 coasters, 4 in diameter, 1/2 in deep)
- One coaster: 3.1416 × 2 × 2 × 0.5 = 6.28 cubic inches
- Six: 37.7 cubic inches
- With 10%: 41.5 cubic inches
- To fluid ounces: 41.5 × 0.554 = 23.0 fl oz, which a 32 fl oz batch covers
Serving tray, 10 × 14 in, 3/4 in deep
- 10 × 14 × 0.75 = 105 cubic inches
- With 10%: 115.5 cubic inches = 64.0 fl oz (2 quarts)
- If you embed dried flowers, measure them by water displacement and subtract that volume rather than guessing.
Silicone Molds and Odd Shapes
Fill the empty mold with water, then measure the water in a measuring cup. That is the exact volume, to which you add the allowance. For curved river channels, measure the width every 6 in, average the widths, and multiply by length and depth.
Mix Ratio and Safety
Use the ratio on the label, and measure the parts accurately. An incorrect ratio can leave the epoxy tacky or improperly cured, according to manufacturers' mixing instructions. The calculator splits the total for you at 1:1, 2:1, 3:1 and 4:1.
Epoxy generates heat as it cures, and TotalBoat notes that foam or glass mixing containers should not be used. Follow the PPE and ventilation instructions on your product's safety data sheet (SDS).
About This Calculator
The MakersMath Resin Calculator takes inches, returns fluid ounces and gallons, and can split Part A and Part B. It handles a rectangle or a circle, in either a mold (single pour) or a surface coat (area × thickness × number of coats). It does not take metric input, irregular channels or embedded objects, so convert metric measurements first and do those subtractions by hand using the methods above.
Key Takeaways
- Look up the maximum pour depth for your product before you calculate the volume.
- Layers affect timing, not total volume. Add the allowance to each mix.
- Mixed resin cannot be saved, so measure the whole job and plan mixes before you start.
- Subtract embedded objects by measuring their displacement.
Ready to run your own numbers? Try our free Resin Calculator.