How the Epoxy Resin Calculator Works
Resin fills a space, so the amount you need is the volume of that space. The calculator works out each shape's volume, adds allowances for losses and sealing, then turns the total into litres, US gallons, weight, and the part A and part B you measure out.
Every cubic centimetre holds one millilitre, so 1,000,000 mm³ is one litre. Weight comes from density: at a typical 1.1 g/cm³, one litre of mixed epoxy weighs about 1.1 kg. Your resin's data sheet gives its own density, ratio, layer depth and recoat time; use those over the typical values here.
The Formulas
1. Volume of each shape
box / flood coat: L × W × depth
round: π × (Ø ÷ 2)² × depth
river: L × average width × depth
average width ≈ (narrowest + widest) ÷ 2
irregular: L × W × fill % × depth
mm³ ÷ 1000 = ml. One cubic inch is 16.387 ml. Multiply by the quantity for sets of coasters or moulds.
2. Total with extras
net = shapes − displacement
total = (net + seal coat) × (1 + waste %)
weight (g) = total (ml) × density (g/cm³)
1 US gallon = 3.785411784 L = 128 US fl oz, 1 US fl oz = 29.5735 ml, 1 lb = 453.59237 g = 16 oz.
3. Part A and part B
by volume: A = total × a ÷ (a + b)
by weight: A volume share = (a ÷ ρA) ÷ (a ÷ ρA + b ÷ ρB)
ρA and ρB are the densities of each part. When they differ, a ratio by weight is not the same ratio by volume. The mixed density from the parts assumes no shrink on mixing.
4. Pours and kits
pours = ceil(depth ÷ max layer)
per pour = volume ÷ pours
kits = ceil(total ÷ kit size)
Layers are split evenly and assume straight sides. A river with sloping live edges takes a little less in its lower layers, so treat the per-pour figure as a guide and mix a touch extra.
Worked Example
River table: 1800 mm long, river 150 mm wide on average, 40 mm deep, 2:1 by volume deep-pour resin
- Volume: 1800 × 150 × 40 = 10,800,000 mm³ = 10.8 L.
- Plus 10 %: 10.8 × 1.1 = 11.88 L (3.14 US gal, or 3 gal 17.7 fl oz).
- Weight at a typical 1.1 g/cm³: 11.88 × 1.1 = 13.07 kg (28.81 lb).
- Split 2:1 by volume: A = 11.88 × 2 ÷ 3 = 7.92 L, B = 11.88 ÷ 3 = 3.96 L.
- Deep-pour resin with a 50 mm maximum layer: 40 ÷ 50 rounds up to 1 pour. With a 25 mm medium-pour resin it would be 2 pours of 20 mm, 5.94 L each.
- In 4 L kits: 11.88 ÷ 4 = 2.97, so 3 kits. Mixing almost 12 L at once is a lot of heat in one bucket, so mix it in batches the data sheet allows.
Practical Tips
- Seal the wood first. Brush a thin coat over the slabs and let it go tacky. Dry wood soaks up resin and pushes air out as bubbles through the pour.
- Build a leak-proof mould. Melamine board or HDPE sheet releases cured epoxy; tape the faces with sheathing or packing tape and run silicone along every inside seam. Plan the panels with the sheet cut optimizer.
- Level the mould. Resin finds level on its own, so a sloping table gives one deep end and one shallow end. Shim the bench until a level reads true both ways.
- Pop bubbles with heat. Pass a heat gun or small torch quickly across the surface a few minutes after pouring. Keep it moving; holding still scorches the resin.
- Do not pour too deep. Keep to the layer depth and recoat window on the data sheet. Pour the next layer while the last one is still within that window so they bond.
- Flatten after curing. Surface the slab with a spoilboard or surfacing bit on a router sled or CNC; the CNC router feeds and speeds calculator gives a starting feed and depth for the cut.
- Safety. Wear nitrile gloves and eye protection, mix and pour with good ventilation, and wear a dust respirator when sanding. Uncured resin can cause skin allergies that last for life.
- Need other units? Use the unit converter. Fitting a steel base or metal inserts? The metal weight calculator works out their weight.
Frequently Asked Questions
Multiply the length by the average river width and the depth, then add about 10 %. A river 1800 mm long, 150 mm wide on average and 40 mm deep holds 10.8 litres, so plan on about 11.9 litres. For a wavy river, average the narrowest and widest points or measure several widths.
Fill the mould with water to the level you want, pour the water into a measuring jug and read the millilitres. That is the resin volume, and it is the most accurate method for odd shapes. Dry the mould completely before pouring resin, because water spoils the cure.
It depends on the resin. Table-top and coating epoxies are typically about 3 mm (1/8 in) per coat, medium casting resins about 12 to 25 mm, and deep-pour resins about 50 mm (2 in) or more. Use the maximum on your data sheet; thicker layers can overheat, crack, yellow or smoke.
Divide each part of the weight ratio by that part's density. For 100:45 by weight with part A at 1.15 g/cm³ and part B at 0.95 g/cm³, that is 86.96 : 47.37, or about 1 : 0.545 by volume. If the densities are not given, weigh the parts on scales instead.
Mixed epoxy is typically about 1.05 to 1.2 g/cm³, so a litre weighs roughly 1.1 kg and a US gallon about 4.2 kg (9.2 lb). Check the density or specific gravity on your resin's data sheet for its exact figure.
Densities, layer depths and allowances shown are typical values and rules of thumb, not data for your resin. Follow the maker's data sheet for ratio, maximum pour depth, temperature and recoat times, and test a small pour first when using a new product.