Castia is an Android app that works out how much epoxy resin your mold needs and how much part A and part B to measure. Type the mix ratio from your label, such as 1:1, 2:1 or 100:45, and choose to mix by volume or by weight. Get the answer in ml, fl oz, grams or ounces, and enter sizes in inches with fractions or in mm and cm. Fill an odd-shaped mold with water and weigh it, and Castia turns that weight into the right amount of resin. Making your own silicone mold? Get the mold box size and the amount of silicone, with the model already taken out. Made and published by GRAMSHIFT.
What you can do with Castia
Resin amount from mold size
Box, round coaster, dome, sphere, cone, ring and river table. For a river table, only the river is counted, not the wood.
Water method for odd molds
Fill the mold with water and weigh it. Castia turns the water weight into the right amount of resin.
Flood coats for tabletops
Work out flood coats for tabletops, paintings and trays, including drips over the edges. A 60 x 40 cm top at 3 mm needs about 720 ml per coat.
Silicone mold making
Get the mold box size from your model plus wall and top thickness, then part A and B of your silicone by volume or weight. Works for platinum-cure and tin-cure.
Pro: recipe card PDF with your logo
Make a recipe card with the piece name, mold drawing, ratio, amounts, cost and your own logo. Print it or send it with a quote.
Pro: price per piece
Set your price per piece from material cost, work time, your hourly rate and markup. Made for resin sellers.
From mold to pour
- Enter the mold shape and size. Use mm, cm or inches with fractions like 1 1/2 or 3/8. Mold of unknown size? Use the water method.
- Enter the ratio on your label. Type 1:1, 2:1, 100:45 or whatever your label says, and pick by volume or by weight. Cup marks give you ml or fl oz, a scale gives you grams or ounces.
- Measure and pour. Follow the step at the bench: "pour A to the 55 ml mark, then add B up to 110 ml", with no re-zeroing in between. Enter the max pour depth to see how many layers you need.
Free and Pro
- Free: every calculation, with no purchase needed. Save results and reuse them next time. A few banner ads on screen.
- Pro (one-time purchase, for resin sellers): price per piece, recipe card PDF with your logo, save as many resins as you like and switch with one tap, no ads.
- Remove ads (one-time purchase): removes the banner ads. No subscription.
- The numbers you enter stay on your device unless you send them yourself. No account, no sign-up or login.
Frequently asked 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 and 10% extra, that is 55 ml of part A and 55 ml of part B.
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 epoxy do I need to coat a tabletop?
Area times thickness. A 60 x 40 cm top at 3 mm needs about 720 ml per coat.
How do I calculate resin for a mold with no straight sides?
Use the water method: weigh the mold full of water. 1 g of water is 1 ml, and Castia turns that into the amount of resin.
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.
Does Castia work with any resin brand?
Yes. You type the mix ratio that is on your label. Enter the density of part A and part B for exact volume-to-weight conversion.
Is Castia free?
Yes. Every calculation is free without buying anything. Pricing, recipe card PDFs and saved resins come with Pro, a one-time purchase.
Do I need an account?
No. There is no account or sign-up, and your numbers stay on your phone.
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.
If something does not work, or you have an idea or a request, feel free to write to us through the contact form or at contact