Work out how much pottery plaster and water to mix for your mould — from cavity dimensions or from a known plaster weight.
Mixing plaster comes down to the ratio of plaster to water. This tool estimates how much of each you need — either from the dimensions of the mould cavity you're filling, or from a target plaster weight — so you mix enough to pour in one go without wasting material.
In Plan mode, enter your cavity's shape and dimensions (rectangular or cylindrical) and the calculator returns the plaster and water to mix. In Weight mode, start from a plaster weight you already know and it gives you the matching amount of water.
Always add plaster to water, never water to plaster, and let it slake for a minute before stirring. Never rinse plaster down a drain — it sets hard inside the pipes; let waste harden in the bucket and bin it instead.
Related: Plaster moulds for pottery · All tools
We use cookies to understand how visitors use Potter's Kit. No personal data is sold or shared.