How Much Resin Do You Need for Coasters?
Updated 2026-10-21
Coasters are one of the most popular first resin projects, and they use surprisingly little material. The trick is to calculate the volume of each coaster, multiply by how many you are making, and add a little extra for the cup and stir stick. This page shows the math so you mix once and don't end up with a half-full mold or a cup of leftover resin.
For a quick answer, open the epoxy resin calculator and choose Circle / cylinder (round coasters) or Rectangle (square coasters). For odd-shaped silicone molds, use the mold volume calculator.
The formulas
Round coaster: V (in³) = π × (diameter ÷ 2)² × thickness
Square coaster: V (in³) = side × side × thickness
Fluid ounces = in³ ÷ 1.8047 ml = in³ × 16.387
Volume per coaster
| Coaster | Volume | Fl oz | ml |
|---|---|---|---|
| 4 in round, 1/4 in thick | 3.14 in³ | 1.74 | 51.5 |
| 4 in round, 3/8 in thick | 4.71 in³ | 2.61 | 77.2 |
| 4 × 4 in square, 1/4 in thick | 4.00 in³ | 2.22 | 65.5 |
| 10 cm round, 0.6 cm thick | 47.1 cm³ | 1.59 | 47.1 |
Worked example: a set of 4 round coasters
- One 4 inch round coaster, 1/4 inch thick: π × 2² × 0.25 = 3.14 in³.
- Four coasters: 3.14 × 4 = 12.57 in³.
- Convert: 12.57 ÷ 1.8047 = 6.96 fl oz (about 206 ml).
- Add 10% for cup and stick residue: 6.96 × 1.10 ≈ 7.66 fl oz (≈ 226 ml).
- 1:1 epoxy: about 3.83 fl oz of Part A + 3.83 fl oz of Part B. 2:1 epoxy: about 5.11 fl oz A + 2.55 fl oz B (by volume).
Square 4 × 4 inch coasters use about 27% more resin than 4 inch rounds of the same thickness (16 in² vs 12.57 in² of area). A set of four at 1/4 inch is 16 in³ ≈ 8.87 fl oz, or about 9.75 fl oz with 10% extra.
Small batches need a bigger waste allowance
When you mix only a few ounces, the resin left on the cup walls and stir stick is a larger share of the batch. For tiny pours, 15–20% extra is reasonable. Many kits also have a minimum recommended batch size for proper curing — check the instructions.
Measure the mold instead of guessing
Silicone coaster molds often have rounded edges, raised rims or a recessed design, so the real volume differs from a simple cylinder. Fill the mold with water, weigh it (grams ≈ ml), then dry it completely. Step-by-step: the water method.
Inclusions reduce resin needed
Dried flowers, wood slices, shells or a cork backing take up space that resin doesn't fill. If an insert is 1/8 inch thick and covers the full face of a 1/4 inch coaster, resin volume is roughly halved. When in doubt, calculate the empty volume and treat the difference as extra buffer.
Avoiding bubbles in coasters
Thin coaster pours are prone to surface bubbles. Mix slowly, pour in a thin stream and pass gentle heat across the surface as the manufacturer allows. More tips: how to fix epoxy bubbles. Also note how long to leave coasters before demolding in epoxy cure time and temperature.
Summary
A standard 4 inch round coaster at 1/4 inch thick holds about 1.7 fl oz (≈ 52 ml) of resin. Multiply by the number of coasters, add 10–20% for small-batch waste, and split by your kit's mix ratio.