Mold Volume Calculator

Work out the volume of a silicone or wooden mould from its shape and dimensions, and how many millilitres of resin it holds.

Resin & Epoxy

A silicone mould is described by its outer dimensions, but what matters is the cavity inside it, which is smaller by the wall thickness on every side. This calculator takes the outer shape, subtracts the walls and the base, and returns the volume the cavity actually holds in cubic centimetres, millilitres and grams. It is a planning and costing tool only.

At a glance

What you enter: Mould shape, Outer length, Outer width, Outer diameter, Outer depth, Wall thickness, Base thickness, How many cavities?, Resin density
What you get: Volume of every cavity, Resin the mould holds, Resin the mould holds, Resin the mould holds
Formula shown: Yes, every step, right below your results.
Cost and privacy: Free, no account needed, and nothing you type is stored.

See worked examples ↓ Read the FAQ ↓ Share this calculator ↓

Mould shape

Outer length cm

Rectangular moulds only. Measure the outside.

Outer width cm

Rectangular moulds only.

Outer diameter cm

Circular and cylindrical moulds.

Outer depth cm

Wall thickness mm

One wall, not both. The tool subtracts a wall from each side and a base from the bottom. Enter zero if you measured the internal faces directly.

Base thickness mm

The floor of the mould. Enter zero for an open frame on a flat surface.

How many cavities?

Resin density g/ml

About 1.05 to 1.2 grams per millilitre for most epoxy products.

Reset

Results are estimates for general information only, always verify with a professional or official source before acting on them.

How to use the Mold Volume Calculator

1 Enter Mould shape
2 Enter Outer length (cm), Rectangular moulds only. Measure the outside.
3 Enter Outer width (cm), Rectangular moulds only.
4 Enter Outer diameter (cm), Circular and cylindrical moulds.
5 Enter Outer depth (cm)
6 Enter Wall thickness (mm), One wall, not both. The tool subtracts a wall from each side and a base from the bottom. Enter zero if you measured the internal faces directly.
7 Enter Base thickness (mm), The floor of the mould. Enter zero for an open frame on a flat surface.
8 Enter How many cavities?
9 Enter Resin density (g/ml), About 1.05 to 1.2 grams per millilitre for most epoxy products.
10 Press Calculate. You get Volume of every cavity, Resin the mould holds, Resin the mould holds, Resin the mould holds, and every intermediate step stays visible under "How is this calculated?"
11 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.

Worked examples

Real numbers run through this calculator. Open any example to load it into the form above and change it.

Rectangular silicone mould

A mould 20 by 15 cm and 3 cm deep with 5 mm walls and a 5 mm base, for one cavity.

You enter

Mould shape: 1
Outer length: 20 cm
Outer width: 15 cm
Outer diameter: 10 cm
Outer depth: 3 cm
Wall thickness: 5 mm
Base thickness: 5 mm
How many cavities?: 1
Resin density: 1.10 g/ml

You get

Volume of every cavity: 665.00 cm3
Resin the mould holds: 665.00 ml
Resin the mould holds: 731.50 g
Resin the mould holds: 22.49 fl oz

The cavity is 19 by 14 by 2.5 cm, about 665 cubic centimetres, so about 665 millilitres or 731 grams.

Open this example in the calculator →

Round mould measured on the inside

A 10 cm round mould 3 cm deep, measured on the internal faces, so no wall or base is subtracted.

You enter

Mould shape: 2
Outer length: 20 cm
Outer width: 15 cm
Outer diameter: 10 cm
Outer depth: 3 cm
Wall thickness: 0 mm
Base thickness: 0 mm
How many cavities?: 1
Resin density: 1.10 g/ml

You get

Volume of every cavity: 235.62 cm3
Resin the mould holds: 235.62 ml
Resin the mould holds: 259.18 g
Resin the mould holds: 7.97 fl oz

A 5 cm radius gives about 236 cubic centimetres, so about 236 millilitres or 259 grams.

Open this example in the calculator →

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Frequently asked questions

How do I work out the volume of a silicone mould?

Measure the outside, then subtract the wall thickness from each side and the base thickness from the bottom. A 20 by 15 cm mould 3 cm deep with 5 mm walls has a cavity of 19 by 14 cm and 2.5 cm, which holds about 665 cubic centimetres, or 665 millilitres. If the walls taper or the cavity is not a simple shape, filling the mould with water and measuring that is more accurate than any formula.

Why does my mould hold less resin than I expected?

Because the walls and the base take up space that the outside dimensions include. On a small coaster mould with 5 mm walls, the cavity can be fifteen to twenty percent smaller than the outside volume. Always work from the cavity, and remember that a poured resin surface also sits slightly below the rim unless you deliberately dome it.

How do I measure the volume of an irregular mould?

Fill it with water, tip the water into a measuring jug, and read the figure. That gives you the true capacity including every curve the shape has, and it costs nothing. Dry rice or fine sand works just as well for a mould you would rather not wet, and both beat estimating an irregular cavity from a formula.

Does the mould material change how much resin it holds?

No, the cavity volume is the cavity volume whatever the mould is made from. What does change is how much resin you lose to the process: a soft silicone mould can distort as you fill it, and a wooden frame with a base can leak at the corners until it is sealed. That is why a waste allowance of 10 to 15 percent belongs on top of any capacity figure.