How much silicone do I need for a cast sleeve?

Short answer: the volume of the outer sleeve body minus the canal it wraps round, plus about 10 %, split into equal parts A and B for the common casting silicones. The designer works the exact number out for your design while you draw it. The calculator below gives a quick, rough upper estimate.

What is sourced and what is not. The 1A:1B ratio and the pot lives come from Smooth-On's product pages. The 10 % extra, and the density of 1.1 g/mL, are working defaults in this tool, not tested figures. Your silicone's datasheet wins on both. For adults (18+).

Quick calculator

The calculator treats the sleeve as a solid round shaft of the widest diameter, with no hole down the middle at all. The real amount of silicone is the outer body's volume minus the canal's, because the core takes up that space during the pour. So this quick figure is well above the true one, more of an overestimate than a real design needs. Treat it as the most you could possibly need for that outer size, not a number to shop by. The designer integrates your actual outer body and canal and shows the exact figure, and the print sheet it writes lists it in millilitres.

Splitting A and B

Ecoflex 00-30, Dragon Skin 10 Medium and Dragon Skin 30 all mix 1A to 1B, by volume or by weight. [Ecoflex 00-30] [DS 10] [DS 30] Other silicones use other ratios, so set the ratio to match your datasheet. Getting it wrong leaves the cast soft, sticky or uncured.

Why mix more than the shape holds

Some of the mix never reaches the sleeve. It stays on the cup and the stirrer, and the two openings beside the core's bar fill as well. That is our reasoning, not a sourced figure, and 10 % is the default the tool starts from; it's already folded into the figure the designer gives you, so there's no need to add your own margin on top. For a first pour, mixing 15 to 20 % extra costs a few millilitres and saves a failed pour. Too little cannot be topped up: a second mix poured onto a half-cured first one leaves a seam.

Do not mix more than you can pour

Pot life starts when the parts meet. Smooth-On lists 20 minutes for Dragon Skin 10 Medium, 45 for Dragon Skin 30 and 45 for Ecoflex 00-30. [DS 10] [DS 30] [00-30] Warmth shortens it. [FAQ 136] If you degas in a vacuum chamber, the mix rises before it falls, so use a cup several times bigger than the volume. [Smooth-On] More on the steps in the guide.

Weighing instead of measuring

A kitchen scale is easier than a syringe. The tool assumes 1.1 g per millilitre to turn volume into grams. That is a typical figure for these silicones, not a measured one: use the density on your datasheet. Because the ratio is 1:1 by weight, weigh half the total into each cup.

Sources

Read on 2026-09-20. Manufacturer pages: Smooth-On. The full list is in docs/GUIDE-SOURCES.md, section 3. See also which silicones suit a sleeve and printing the mould and the core.