Castia Epoxy Resin Calculator

How much epoxy resin do you need for your mold? Enter the mold size and Castia tells you how much part A and part B to measure — in ml, fl oz, grams or ounces, for any brand and any mix ratio.

Mold of unknown size? Fill it with water, weigh it, and Castia turns the water weight into the right amount of resin.

Making your own silicone mold? Enter the size of your model and Castia gives you the mold box size and how much mold-making silicone to mix, with the model's volume already taken out.

WHAT YOU GET
- Mold volume from its size: box, round coaster, dome, sphere, cone, ring and river table (only the river is counted, not the wood).
- Part A and part B for any ratio: 1:1, 2:1, 3:1, 100:45 or whatever your label says.
- Mix by volume or by weight. Measuring with cup marks? You get ml or fl oz. Measuring on a scale? You get grams or ounces.
- A step you can follow at the bench: "pour A to the 55 ml mark, then add B up to 110 ml". On a scale it works the same way, with no re-zeroing in between.
- Flood coats for tabletops, paintings and trays, including drips over the edges.
- Water method for molds you cannot measure.
- UV resin (one part) mode.
- Silicone mold making: mold box size from your model plus wall and top thickness, then part A and B of your silicone (platinum-cure or tin-cure) by volume or weight, using the ratio on your label, such as 1:1 or 100:5.
- Model volume from its size, by sinking it in water, or from its weight and density.
- How many pours: enter the max pour depth from your label and see how many layers you need.
- Exact volume-to-weight conversion when you enter the density of part A and part B.
- Pigment amount, extra for what stays in the cup, cost per piece.
- Inches with fractions (1 1/2, 3/8) as well as mm and cm.
- Save results and reuse them next time.

WHY CASTIA
- Works with every brand. You type what is on your label.
- No account, no sign-up. Your numbers stay on your phone.
- Works offline.
- Few ads, removed for good with a single purchase. No subscription.
- 19 languages.

CASTIA PRO (ONE-TIME PURCHASE, FOR RESIN SELLERS)
- Price per piece from material cost, work time, your hourly rate and markup.
- Recipe card PDF with the piece name, mold drawing, ratio, amounts, cost and your own logo. Print it or send it with a quote.
- Save as many resins as you like and switch with one tap.
- No ads.
Every calculation stays free without buying.

QUESTIONS
How much resin do I need for a 10 x 10 x 1 cm mold?
100 ml of mixed resin, plus a little extra for the cup. With a 1:1 ratio that is 55 ml of A and 55 ml of B with 10% extra.

Is 1:1 by volume the same as 1:1 by weight?
No. Part A is usually heavier than part B, so the weight ratio is different. Choose "by volume" or "by weight" exactly as your label says, and enter both densities if you want the other unit to be exact.

How much resin to coat a tabletop?
Area times thickness. A 60 x 40 cm top at 3 mm (1/8 inch) needs about 720 ml per coat.

My mold has no straight sides. What now?
Use the water method: weigh the mold full of water. 1 g of water is 1 ml.

How much silicone do I need to make a mold?
Mold box volume minus the model's volume. A 5 x 5 x 5 cm model with 1 cm walls and 1 cm on top needs a 7 x 7 x 6 cm box and 169 ml of silicone, not 294 ml.

GOOD TO KNOW
Results are a guide. Always follow the mix ratio, maximum pour depth, cure time and safety advice of your product. Wear gloves and work in a ventilated room.

Recent changes:
New: Silicone mold calculator. Enter your model's size to get the mold box size and how much silicone (A and B) to mix.
Improved display at larger font sizes.