Silicone Mixing Ratio Calculator
The ratio depends on which family of silicone you have. Platinum (addition) cure is usually 1 : 1, so the total simply halves; tin (condensation) cure uses a small catalyst charge, typically 10 : 1 or 100 : 5, which is 20 : 1. Five hundred grams at 10 : 1 is 454.5 g of A and 45.5 g of B, with the catalyst at 9.1% of the batch. The same 500 g at 1 : 1 is 250 g each and a 50% catalyst share — a completely different weigh-out, which is why halving the total without reading the tin is the classic mistake. These are weight ratios; plenty of products print a volume ratio too, so use the weight figure when you work on a scale. The arithmetic matches the resin mix tool, but silicone is far less forgiving in small batches because the catalyst sits so heavily on one side.
Your numbers
Part A
454.5g
Part B
45.5g
Catalyst share
9.1%
Formula
Part A = Silicone needed × Ratio part A ÷ (Ratio part A + Ratio part B)
When the catalyst side is only 45 g, being 1 g out is a 2% error on its own — use a scale reading to 0.1 g and never dose part B by eye. Short on catalyst and the mould stays tacky inside and will not release; long on it and the pot kicks before you have finished pouring. Platinum cure is also sensitive to contamination: sulphur-based clay, latex gloves, or a cup that held tin-cure will leave a permanently uncured patch, so test a hidden corner if you are unsure of the master. Never mix the two families. Weigh 5% extra as well — silicone poured in two goes splits along the join.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Silicone needed (g)Silicone needed — the box volume less the model. | 500 | 0 and up |
| Ratio part AThe A side of the mix ratio. | 10 | 0 and up |
| Ratio part BThe B side of the mix ratio. | 1 | 0 and up |
Step by step
Quick reference table
Results when only Silicone needed (g) changes and everything else stays put.
| Silicone needed (g) | Part A (g) | Part B (g) | Catalyst share (%) |
|---|---|---|---|
| 250 | 227.3 | 22.7 | 9.1 |
| 375 | 340.9 | 34.1 | 9.1 |
| 500 | 454.5 | 45.5 | 9.1 |
| 750 | 681.8 | 68.2 | 9.1 |
| 1,000 | 909.1 | 90.9 | 9.1 |
What each result means
| Result | At default values |
|---|---|
| Part A (g)How much part A to weigh out. | 454.5 |
| Part B (g)How much part B; eyeballing this is why resin fails to cure. | 45.5 |
| Catalyst share (%)The catalyst's share of the batch — 50% for platinum cure, 5–10% for tin. | 9.1 |
Common mistakes
When the catalyst side is only 45 g, being 1 g out is a 2% error on its own — use a scale reading to 0.1 g and never dose part B by eye. Short on catalyst and the mould stays tacky inside and will not release; long on it and the pot kicks before you have finished pouring. Platinum cure is also sensitive to contamination: sulphur-based clay, latex gloves, or a cup that held tin-cure will leave a permanently uncured patch, so test a hidden corner if you are unsure of the master. Never mix the two families. Weigh 5% extra as well — silicone poured in two goes splits along the join.
Glossary
- Silicone needed
- Silicone needed — the box volume less the model.
- Ratio part A
- The A side of the mix ratio.
- Ratio part B
- The B side of the mix ratio.
- Part A
- How much part A to weigh out.
- Part B
- How much part B; eyeballing this is why resin fails to cure.
- Catalyst share
- The catalyst's share of the batch — 50% for platinum cure, 5–10% for tin.
Frequently asked questions
Q. How is Silicone Mixing Ratio Calculator calculated?
Part A = Silicone needed × Ratio part A ÷ (Ratio part A + Ratio part B) — The ratio depends on which family of silicone you have. Platinum (addition) cure is usually 1 : 1, so the total simply halves; tin (condensation) cure uses a small catalyst charge, typically 10 : 1 or 100 : 5, which is 20 : 1. Five hundred grams at 10 : 1 is 454.5 g of A and 45.5 g of B, with the catalyst at 9.1% of the batch. The same 500 g at 1 : 1 is 250 g each and a 50% catalyst share — a completely different weigh-out, which is why halving the total without reading the tin is the classic mistake. These are weight ratios; plenty of products print a volume ratio too, so use the weight figure when you work on a scale. The arithmetic matches the resin mix tool, but silicone is far less forgiving in small batches because the catalyst sits so heavily on one side.
Q. Can you walk through an example?
With Silicone needed 500g, Ratio part A 10, Ratio part B 1, the answer is Part A 454.5g.
Q. What do I need to enter?
Enter Silicone needed, Ratio part A, Ratio part B. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Silicone needed (g) moves the answer to Silicone needed (g) 250 → Part A (g) 227.3 and Silicone needed (g) 1,000 → Part A (g) 909.1. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
When the catalyst side is only 45 g, being 1 g out is a 2% error on its own — use a scale reading to 0.1 g and never dose part B by eye. Short on catalyst and the mould stays tacky inside and will not release; long on it and the pot kicks before you have finished pouring. Platinum cure is also sensitive to contamination: sulphur-based clay, latex gloves, or a cup that held tin-cure will leave a permanently uncured patch, so test a hidden corner if you are unsure of the master. Never mix the two families. Weigh 5% extra as well — silicone poured in two goes splits along the join.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.