Volume first, then the ratio
A mold's volume in millilitres is the same as its size in cubic centimetres: length × width × depth for trays and coasters, π × r² × depth for round molds. For complicated silicone molds, fill the mold with water, then pour the water into a measuring jug, or weigh it (1 g of water ≈ 1 ml). Dry the mold completely before pouring resin.
Example: four 10 × 10 cm coasters, 0.6 cm deep, are 60 ml each. With 10% extra, mix 264 ml in total: 132 ml of part A and 132 ml of part B at a 1:1 volume ratio.
Volume ratio vs weight ratio
Resin systems specify their mix ratio either by volume or by weight, and the two aren't interchangeable, because resin and hardener have different densities. Use exactly the ratio on your product's data sheet, and choose "by weight" when the sheet gives weights. Mixed epoxy typically weighs 1.05–1.2 g per ml, so the default of 1.1 is only for estimating total weight and cost. An off-ratio mix may never fully cure.
Pour depth and safety
Coating and doming resins are made for thin layers, often 3–6 mm per pour. Deep-pour resins can go thicker. Too deep a pour of the wrong resin can overheat, crack or yellow. Wear nitrile gloves, work in a ventilated room, and follow the product's safety data sheet.
Questions
- How much resin per square foot?
- A layer 1/8 inch (3.2 mm) thick over one square foot is 18 cubic inches, about 10 US fl oz (295 ml) of mixed resin, plus waste. Use the rectangle shape with your dimensions and a depth of 0.32 cm.
- Why add extra?
- Resin clings to cups, sticks and the mold edges. 10% covers most small pours; complex molds and many small cavities may need 15–20%.
- Can I mix by volume if the ratio is by weight?
- Not reliably. Convert with each part's density from the data sheet, or use a scale.