Glaze Specific Gravity Calculator (How Much Water to Add)

A glaze specific gravity calculator turns a quick weighing into a clear answer: divide the weight of your glaze sample in grams by its volume in milliliters to get the SG, then estimate the water to add with volume × (current SG − target SG) ÷ (target SG − 1). Enter your numbers below for an estimate.

How to use the glaze specific gravity calculator

1. Stir the glaze thoroughly so nothing has settled on the bottom of the bucket.
2. Put a container on a gram scale and tare it, then pour in a measured volume of glaze, such as 100 mL from a graduated cylinder. Enter the weight and the volume. If you already know the SG from a hydrometer, choose “I already know the SG” instead.
3. Enter how much slurry is in the whole bucket, in liters or US gallons.
4. Pick a target. Use a published preset or enter your own target SG, for example the number printed on a commercial glaze’s instructions.
5. Press Calculate. The tool shows the current SG, an estimate of how much water to add (or remove), and an estimate of how much dry material is in the bucket. If an entry can’t work, a message explains what to fix.
6. Add water in small steps, stir, and re-measure before you glaze.

The formula: how much water to add to glaze

Specific gravity is the weight of your glaze compared with the same volume of water. Water has an SG of 1.0, which means 1 gram per milliliter, so a 100 mL sample that weighs 142 g has an SG of 1.42. AMACO describes the same method: glaze weight ÷ water weight = specific gravity.

The water calculation is a simple mass balance. If you have V liters of slurry at SG₁ and add w liters of water (SG 1.0), the new SG is (V × SG₁ + w) ÷ (V + w). Solving for the target SG₂ gives:

Water to add = V × (SG₁ − SG₂) ÷ (SG₂ − 1)

If the target is higher than the current SG, the glaze is too thin. The same equation, with the sign reversed, estimates how much clear water you need to take off after the glaze settles. It assumes the water you remove carries no glaze material, so pour gently and re-measure. Because a slurry is dry material plus water, both the current and the target SG must be below the dry-material SG; the calculator flags entries that break this.

The dry-material estimate uses Brongniart’s formula. Per liter of slurry, dry grams ≈ 1000 × (SG − 1) × S_dry ÷ (S_dry − 1). With the typical dry SG of 2.6, this simplifies to 1625 × (SG − 1), so a glaze at SG 1.50 holds roughly 812 g of dry material per liter. Treat this number as an estimate.

Glaze specific gravity chart and glaze thickness

SG tracks slurry density, meaning how much solid material each liter carries, and it helps you reproduce a glaze setup you have already established. It does not by itself determine viscosity or how thick a coat ends up on the pot, so use it alongside your own test tiles. The table below lists only ranges that the cited sources publish. We did not find a published brushing or spraying SG in these sources, so the calculator has no preset for those. Enter your own target if you work that way.

When you mix a dry glaze from scratch, Laguna notes that roughly 8 to 11 ounces of water per pound of dry glaze is typical, but the amount varies by glaze. That is why measuring SG after mixing and then using a how-much-water-to-add calculator works better than following a fixed recipe. AMACO recommends adding water 60 mL (¼ cup) at a time until you reach the right range.

Heavy materials raise the dry SG. If your glaze has a lot of tin, zinc or other dense oxides, enter a higher dry-material SG to improve the dry-content estimate. Some reference values from the Glazy wiki are listed below.

Methodology & sources

The calculator treats water as SG 1.0 (1 g per mL), applies a mass balance to estimate the water to add or remove, and uses Brongniart’s formula with a default dry SG of 2.6 for the dry-content estimate. It decides whether to add or remove water from the unrounded SG values and shows SG to four decimals. US gallons are converted at 3.785411784 L, and 1 US gallon equals 128 US fl oz.

• Glazy Help — Specific Gravity: definition and target ranges
• AMACO — Dry Form Dipping Glaze mixing and using instructions: measurement method and the 1.41–1.43 range
• Digitalfire Reference Library — Specific gravity: water SG 1.0
• Glazy Ceramics Wiki — Brongniart’s formula: dry-content estimate
• Glazy Ceramics Wiki — Specific gravity of glaze materials
• Laguna Clay — Dry glaze mixing instructions
• Wikipedia — Gallon: unit conversion

Last updated: November 2026

FAQ

What specific gravity should my glaze be?

Glazy suggests 1.4–1.5 as a good starting point for most glazes, adjusted anywhere from 1.25 to 1.6. AMACO lists 1.41–1.43 for its dry-form dipping glazes. Always follow the maker’s instructions for a commercial glaze.

How do I measure glaze specific gravity?

Weigh a known volume of well-stirred glaze in grams and divide by the weight of the same volume of water. Since 1 mL of water weighs 1 g, 100 mL of glaze weighing 142 g has an SG of 1.42.

How much water do I add to lower the specific gravity?

Water to add = slurry volume × (current SG − target SG) ÷ (target SG − 1). For 10 L at SG 1.50 brought down to 1.40, that is 10 × 0.10 ÷ 0.40 = 2.5 L of water.

What if my glaze is too thin?

You cannot thicken a glaze by adding water, so you need to remove water. Let the glaze settle, pour or sponge off the clear water on top, and re-measure; the calculator estimates how much water to take off.

How accurate is the dry material estimate?

It uses Brongniart’s formula with an average dry-material SG of 2.6, which Glazy says fits most glazes. Glazes with a lot of tin or lead are heavier, so treat the figure as an estimate.

Related guides

• How to Mix Dry Glaze Powder for Ceramics
• How to Glaze Pottery for an Even, Finished Surface
• Is Reactive Glaze Safe for Pottery?