Tumbler epoxy calculator

Tumbler coats are thin, and every time you mix, some epoxy stays stuck in the mixing cup however many tumblers the batch is for. The calculator counts that once per batch, plus a small allowance for the stir stick and gloves. If you sell tumblers, the tumblers-per-kit figure is your material cost.

How the tumbler estimate works

The coated surface is the side of a cylinder: π × diameter × height. Multiply by the thickness of one coat and you have the epoxy that ends up on the tumbler. The rest of each batch is lost in two ways. A fixed amount stays in the mixing cup every time you mix — about 0.2 fl oz (6 ml) by default, the same whether the batch is for one tumbler or six. A smaller share, 5% by default, goes on the stir stick, your gloves and drips. You mix one batch per coat, so the cup loss is paid once per coat, not once per tumbler.

side area = π × diameter × coated height
per coat (one batch) = area × coat thickness × tumblers × (1 + waste) + cup loss
tumblers per kit = (kit size ÷ coats − cup loss) ÷ (area × coat thickness × (1 + waste))
1 fl oz = 29.6 ml

A typical 20 oz skinny tumbler is about 2.9 in across with around 8¼ in of coated height — roughly 75 sq in. At a typical coat of about 1/50 in (0.5 mm), that’s about 25 ml on the tumbler, or about 32 ml (just over 1 fl oz) to mix once the allowance and cup loss are added. Two coats is about 64 ml, so a 16 fl oz (473 ml) kit does seven tumblers coated one at a time — or eight if you coat them together from one batch per coat, because the cup loss is then paid once instead of eight times. That is what the tumblers-per-kit figure assumes; the note under the result gives the one-at-a-time count. Six tumblers at once take about 161 ml a coat. The full breakdown is in how much epoxy for a 20 oz skinny tumbler; a tapered cup is worked through in how much epoxy for a 30 oz tumbler.

Why the numbers are approximate

Coat thickness on a spinning cup depends on the epoxy’s viscosity, how long you spread it, the room temperature and how fast the turner spins. The three thickness options are ballpark figures. KS Resin, a resin maker, gives a rule of thumb of 1–1.5 ml of epoxy per ounce of tumbler capacity; the calculator works from the coated surface instead, which is why a wide 30 oz cup doesn’t come out 50% higher than a 20 oz skinny. After your first cup, weigh the mixing cup before and after to see what really stays behind, and nudge the thickness or the cup loss (under More options) to match your own technique. Measure your actual tumbler — sizes vary between brands even at the same capacity, and tapered cups should use an average diameter.

Tips

• Use an epoxy made for tumblers or thin coatings; the label will give the recoat window between coats.
• Mix at least the minimum batch size the manufacturer lists. Tiny batches are easy to get off-ratio — coating two or three tumblers from one batch helps.
• Keep the room warm and steady. ArtResin suggests working at about 75–85°F (24–30°C); cold epoxy is thick, goes on heavier and sags.
• Tape the rim and bottom band cleanly — a crisp tape line is most of what makes a tumbler look finished.
• Let the final coat cure fully, per the label, before washing or using the cup, and hand-wash it: ArtResin puts cured resin’s heat tolerance at about 120°F, and dishwashers can run hotter.