Before You Mix
The calculator supports your planning; it does not replace your resin manufacturer’s instructions.
- Follow the manufacturer’s Part A:Part B mix ratio.
- Confirm whether that ratio is by weight or by volume.
- Check the maximum pour depth and batch size.
- Check the working time before you start mixing.
How to Measure Mold Capacity
- Place the mold on a level surface.
- Fill the cavity with a measurable liquid suitable for the mold.
- Record the volume and whether it represents one cavity or the entire mold.
- Empty the mold completely.
- Make sure the mold is fully dry before resin use.
How the Calculator Works
Mold Capacity
Start with the volume your mold holds. The calculator applies cavities and mold quantity, then fill, then extra allowance to find the total mixed resin volume.
Dimension Estimate
Choose a simple solid shape and enter inside dimensions. Dimension results are labelled Estimated / ≈. Irregular, hollow and complex shapes need measured capacity instead.
Mix Ratio
The selected A:B ratio splits the total mixed amount. By volume splits the mixed volume; By weight splits only a total mixed weight you provide. No ml ↔ g conversion is performed.
Show formulas
Use centimeters for these volume formulas; the result is in ml. Radius is half the diameter.
- Rectangle: Length × Width × Depth
- Round: π × radius² × depth
- Oval: π × (length / 2) × (width / 2) × depth
- Sphere: 4/3 × π × radius³
- Hemisphere: 2/3 × π × radius³
Common Calculation Mistakes
- Using outside silicone mold dimensions. Measure the cavity or finished solid casting.
- Treating weight and volume ratios as the same. Match the manufacturer’s specified basis.
- Forgetting extra resin allowance. Allow for resin left in mixing tools without changing the mix ratio.
- Estimating irregular molds from a bounding box. Measure the cavity capacity instead.
- Ignoring manufacturer limits. Check pour depth, batch size and working time even when the numbers calculate correctly.
FAQ
How much extra resin should I mix?
The calculator starts with a 10% allowance for resin left in the cup or on the stirring stick and small measurement differences. Adjust it from 0% to 50% for your project. Extra allowance increases the total mixed amount; it does not change the A:B ratio.
Can I convert ml to grams for resin?
There is no universal ml-to-grams conversion for resin. This calculator never automatically converts ml to g. In By weight mode, enter a known total mixed weight. If it is unavailable, you can still see the volume requirement, but the weight split remains unavailable.
Is 1:1 by weight the same as 1:1 by volume?
Do not treat them as interchangeable. Equal volumes and equal weights are different instructions. Choose the basis and Part A:Part B ratio specified by your resin manufacturer; changing the basis does not convert one ratio into the other.
Can I use outside mold dimensions?
Use the inside cavity dimensions or the dimensions of the finished solid casting. Outside silicone measurements include mold walls and can overstate the space resin will fill. If you cannot measure that space accurately, use measured mold capacity instead.
How do I calculate an irregular mold?
Use Known Capacity and measure the actual cavity volume. A rectangular bounding box includes space outside an irregular shape, so it is not a reliable substitute for the amount of resin the cavity holds.
What if my mold has multiple cavities?
For equal cavities, choose One cavity, enter capacity per cavity, then set Cavities being filled and Mold quantity. If you measured the entire mold, choose Entire mold. Calculate different-sized cavities separately rather than assuming they all hold the same amount.
Does this calculator work for hollow molds?
Use Known Capacity for the actual space resin will fill, excluding any core or void. The dimension formulas estimate simple solid shapes; they do not subtract hollow spaces or calculate shell thickness.
Does it account for pigments or inclusions?
No. Pigments and inclusions are not automatically deducted from the resin volume, and the calculator does not assess their compatibility. Account for your actual fill space and follow the resin manufacturer’s additive limits.
More Free Resin Tools
Resin Mold Calculator is the free tool currently available here.