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Never Guess Again: The Clay Shrinkage Calculator Every Potter Needs

Clay shrinkage is my biggest enemy at the moment. I’ll make an AWESOME, HUGE mug, thinking it will at least be 10 oz, and it turns out to be a very normal 8 oz size. So, if you’ve ever been puzzled by how much your clay piece shrinks after firing, you’re not alone. But, we have good news! I explained my constant dilemma to my dad, and he created our handy clay shrinkage calculator. It’s a simple tool to help you figure out the right size to start with, so your finished piece turns out just how you want it. And we’re sharing it for free!

Jump to the calculator!

When you fire clay, it typically shrinks between 5% and 20%. Why does this happen? As clay dries and fires, it loses water and undergoes physical and chemical changes. Here are a few things that influence shrinkage: 

Type of Clay: Different types of clay, such as earthenware, stoneware, and porcelain, have varying shrinkage rates due to their unique compositions.

  • Earthenware: typical shrinkage rate of around 5% to 8%
  • Stoneware: typical shrinkage rate of around 10% to 12%
  • Porcelain: typical shrinkage rate of around 12% to 15%

Drying Process: The rate and duration of drying can affect the amount of shrinkage. Faster drying can lead to more shrinkage.

Firing Temperature:  The higher the firing temperature, the more the clay shrinks. However, after reaching a certain point, the clay swells before eventually melting.

Getting your measurements right is crucial in pottery. A small error in sizing can lead to a big difference in your final piece. Knowing your clay’s shrinkage percentage and using a clay shrinkage calculator can save you from potential disappointments!

Our calculator is here to take the guesswork out of your pottery projects. Just pop in your project details, hit calculate, and you’ll know the perfect starting size to achieve your desired final dimensions.

Clay Shrinkage Calculator

Clay Shrinkage Calculator


Here are the wet clay sizes based on the total effective shrinkage entered:

Wet Height:

Wet Width:

Wet Depth:

Want to figure out shrinkage on your own? Here’s a quick guide:

Drying Shrinkage Formula:

Drying Shrinkage (%) = ((Initial Dimension – Dry Dimension) / Initial Dimension))×100


  1. Prepare a Test Strip: Create a small piece of clay with known dimensions.
  2. Measure the dimensions of the wet clay piece.
  3. Let the clay dry completely.
  4. Measure the dimensions again after drying.
  5. Use the formula above to calculate the percentage of shrinkage.

Firing Shrinkage Formula:

Firing Shrinkage (%) = ((Initial Dimension – Fired Dimension) / Initial Dimension)×100


  1. Bisque Firing: Fire the dried clay piece in a bisque firing. This is usually the first firing at a relatively low temperature.
  2. Measure Bisque Dimensions: Measure the dimensions of the bisque-fired piece.
  3. Use the formula above to determine the percentage of shrinkage during firing.

There you have it! With our clay shrinkage calculator and these insights, you’re all set to tackle your pottery projects with confidence. Say goodbye to unexpected shrinking surprises and hello to perfectly sized creations. Happy potting! 🏺


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