Glass Quantity Calculator

This calculator helps estimate how much glass you need to fill a casting mold or mould to a chosen level. You can calculate the required amount by entering a water-fill volume, measuring a rectangular, round, or oval mold, or entering your own custom volume.

The calculator converts the mold volume into an estimated glass weight using a selected glass factor, also known as specific gravity. Presets are included for common glass types such as Bullseye compatible glass, System 96 / Oceanside / Uroboros, Wissmach COE 96, float / soda-lime glass, and borosilicate glass. You can also enter a custom factor if you have a manufacturer’s published value or want to use your own tested figure.

Use the optional allowance setting if you want to add extra glass for trimming, coldworking, loss, or other practical needs. The result gives both the exact calculated amount and a rounded-up suggested weigh-out amount.

Please remember that this is an estimating tool only. It does not replace manufacturer guidance, test firings, kiln schedules, annealing requirements, mold preparation, or normal kiln safety procedures. Glass compatibility is not determined by COE alone, and different brands, colours, forms, and batches may behave differently. Always use glass that is known to be compatible for your project, and test when needed.

For irregular molds, a volume-measurement method such as water fill or dry displacement is usually more accurate than measuring the mold dimensions. If water is used with a porous mold, make sure the mold is completely dry before firing. Wet molds can cause firing problems and may damage the mold, glass, or kiln.