Find out how big your pot will be after the kiln, or how big to make it. Enter a wet size and your clay's shrinkage for the fired size and capacity, enter a target fired size for the size to throw, or measure a test tile to find your clay's real shrinkage.
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What do you want to find?
Use the total (wet to fired) shrinkage from your clay's data sheet or a test tile.
%
Mark a line (e.g. 10 cm) on a fresh slab.
Enter your values to see the result.
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How to use the Clay Shrinkage Calculator
Choose what to find: fired size, throw size, or the shrinkage of your clay from a test tile.
Pick your clay body or type the shrinkage % from the data sheet.
Enter the sizes you know: height, width or diameter, depth and capacity.
Read the results and use the shrinkage ruler when you throw or build.
Example: a 10 in plate in a 12% stoneware must be made 10 ÷ 0.88 = 11.36 in wide. A bowl that holds 1 liter wet will hold 1 × 0.88³ ≈ 0.68 liters after firing.
Typical shrinkage by clay body
Clay body
Typical total shrinkage
Make it this much bigger
Capacity kept after firing
Low-fire earthenware (cone 06–04)
5–8%
+5.3% to +8.7%
78–86%
Mid-fire stoneware (cone 5–6)
10–13%
+11.1% to +14.9%
66–73%
High-fire stoneware (cone 10)
11–14%
+12.4% to +16.3%
64–70%
Porcelain
12–16%
+13.6% to +19.0%
59–68%
These are typical ranges, not specifications. Your clay, its water content and your kiln all matter, so a test tile is the most reliable number.
How to make a shrinkage test tile
Roll a slab from the same clay you use for pots, at your usual thickness.
Scratch a straight line exactly 10 cm (or 4 in) long and mark both ends clearly. Write the clay name on the tile.
Measure again when it is bone dry, and again after the glaze firing at your usual cone.
Make two or three tiles and average them; a single tile can warp or be measured slightly wrong.
Frequently asked questions
How do you calculate clay shrinkage?
Mark a line of known length on a wet test tile, let it dry and fire it, then measure again. Shrinkage % = (wet length − fired length) ÷ wet length × 100. A 10 cm line that fires to 8.8 cm has shrunk 12%.
How big should I throw a mug to account for shrinkage?
Divide the fired size you want by (1 − shrinkage). For a 4 in tall mug in a clay that shrinks 12%, throw it 4 ÷ 0.88 = 4.55 in tall. Simply adding 12% (4.48 in) is not quite enough.
How much does a mug's capacity shrink?
Capacity is a volume, so it shrinks by the cube of the linear factor. With 12% linear shrinkage, the volume is 0.88³ = 0.68 of the wet volume, about 32% less. A mug that holds 12 oz when wet will hold only about 8.2 oz after firing.
How much do different clays shrink?
Typical total shrinkage is about 5–8% for low-fire earthenware, 10–13% for mid- and high-fire stoneware and 12–16% for porcelain. Values depend on the exact clay body and the firing temperature, so check the supplier's data sheet or test your own.
What is the difference between drying and firing shrinkage?
Drying shrinkage happens as water leaves the clay between wet (plastic) and bone dry, often about 5–7%. Firing shrinkage happens in the kiln as the clay vitrifies. Total shrinkage is the change from wet to fired, which is what you need for sizing.
Does firing hotter make clay shrink more?
Usually yes. Firing a clay body to a higher cone makes it more vitrified and denser, so it shrinks more. Underfiring a stoneware leaves it more porous and slightly larger.
Why does my pot shrink unevenly?
Uneven wall thickness, drying one side faster, or the base sticking to the shelf can make parts shrink by different amounts, which can cause warping or cracks. Dry slowly and evenly, and keep walls consistent.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.