Silicone Mould Calculator
The silicone is whatever the model does not fill. The most reliable way to get the model volume is displacement: drop it into a full cup of water and measure what overflows. A 500 mL box around a 120 mL model needs 380 mL of silicone, which at a density of 1.15 is 437 g. Measure the box on the inside — width × depth × height in centimetres is millilitres.
Your numbers
Silicone needed
437g
Mould volume
380mL
Formula
Silicone needed = (Container volume − Model volume) × Resin density
Leave at least a centimetre of silicone between the model and the walls. Thin walls let the mould splay so resin leaks, and they tear after a few pours. Silicone is also an A : B mix, so run this weight through the mix ratio tool, and add 5% for what stays in the cup — a silicone pour joined halfway through splits at the join.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Container volume (mL)What the vessel holds; filling it with water is the accurate way. | 500 | 1 and up |
| Model volume (mL)The volume of the model you are moulding. | 120 | 0 and up |
| Resin density (g/cm³)Grams per cm³ — epoxy sits near 1.1. | 1.15 | 0.8 ~ 1.6 |
Step by step
Quick reference table
Results when only Container volume (mL) changes and everything else stays put.
| Container volume (mL) | Silicone needed (g) | Mould volume (mL) |
|---|---|---|
| 250 | 150 | 130 |
| 375 | 293 | 255 |
| 500 | 437 | 380 |
| 750 | 725 | 630 |
| 1,000 | 1,012 | 880 |
What each result means
| Result | At default values |
|---|---|
| Silicone needed (g)Silicone needed — the box volume less the model. | 437 |
| Mould volume (mL)What the mould holds; measure it with water. | 380 |
Common mistakes
Leave at least a centimetre of silicone between the model and the walls. Thin walls let the mould splay so resin leaks, and they tear after a few pours. Silicone is also an A : B mix, so run this weight through the mix ratio tool, and add 5% for what stays in the cup — a silicone pour joined halfway through splits at the join.
Glossary
- Container volume
- What the vessel holds; filling it with water is the accurate way.
- Model volume
- The volume of the model you are moulding.
- Resin density
- Grams per cm³ — epoxy sits near 1.1.
- Silicone needed
- Silicone needed — the box volume less the model.
- Mould volume
- What the mould holds; measure it with water.
Frequently asked questions
Q. How is Silicone Mould Calculator calculated?
Silicone needed = (Container volume − Model volume) × Resin density — The silicone is whatever the model does not fill. The most reliable way to get the model volume is displacement: drop it into a full cup of water and measure what overflows. A 500 mL box around a 120 mL model needs 380 mL of silicone, which at a density of 1.15 is 437 g. Measure the box on the inside — width × depth × height in centimetres is millilitres.
Q. Can you walk through an example?
With Container volume 500mL, Model volume 120mL, Resin density 1.15g/cm³, the answer is Silicone needed 437g.
Q. What do I need to enter?
Enter Container volume, Model volume, Resin density. 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 Container volume (mL) moves the answer to Container volume (mL) 250 → Silicone needed (g) 150 and Container volume (mL) 1,000 → Silicone needed (g) 1,012. 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?
Leave at least a centimetre of silicone between the model and the walls. Thin walls let the mould splay so resin leaks, and they tear after a few pours. Silicone is also an A : B mix, so run this weight through the mix ratio tool, and add 5% for what stays in the cup — a silicone pour joined halfway through splits at 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.