Does this only account for shrinkage between bisque and final, or the whole process from wet clay?

It applies your entered shrinkage rate (%) directly between the bisque size and the final size fields. If you know the total shrinkage rate from the wet/forming stage instead, you can enter your forming size into the bisque field and use it the same way.

What happens if both sides already have values and I change one?

The field you just edited becomes the new reference, and the opposite field recalculates and updates automatically.

What's a typical clay shrinkage rate?

It varies by clay body, but it's generally around 5-15%, with some kaolin-heavy or porcelain bodies shrinking as much as 15-20%. Check your clay manufacturer's spec sheet or run a test firing for the most accurate number.

Should the shrinkage rate include shrinkage from before bisque firing (right after forming)?

No — the shrinkage rate here is based on the bisque size. If you know the total shrinkage from right after forming all the way to the final firing, you can use that by entering the as-formed size in the "bisque size" field instead.

Can I calculate just one of width, depth, or height?

Yes, each dimension is calculated independently, so you only need to enter the ones you need.

Could the shrinkage rate be negative or over 100%?

No, clay shrinkage is always a positive value between 0 and 100%. The typical range is around 5-20%.

Clay Shrinkage Calculator - Bisque & Final Size

What is a clay shrinkage calculator?

Clay keeps shrinking as it goes through bisque firing and then glaze (final) firing, typically somewhere between 5-20% depending on the clay body. The Clay Shrinkage Calculator takes either your bisque-stage size or your finished final size — whichever you know — and calculates the other automatically using the formula "final size = bisque size × (1 − shrinkage rate)". Width, depth, and height can each be calculated in either direction, so you can preview what an already-bisqued piece will measure once fired, or work backward from a target final size to see how big it needs to be at the bisque stage.

How to use it

Enter your clay's shrinkage rate (%), or tap one of the common-rate preset buttons to select one quickly. Then enter whichever you know — bisque size or final size — into the width, depth, and height fields, and the other side fills in automatically. If both sides already have values and you edit one of them, the other recalculates based on your latest edit. Once width and height are available, two pottery silhouettes are drawn to scale so you can compare the sizes at a glance.

When it comes in handy

Previewing what size an already-bisqued piece will end up after the final firing
Working out how big to make something at the bisque stage to hit a target final size
Recalculating sizes when switching to a new clay body with a different shrinkage rate
Comparing bisque and final sizes at once for work where width, depth, and height all matter

Why does clay shrink differently at bisque and final firing?

Clay shrinkage actually happens in two separate stages, not one. As a piece dries after forming, moisture escapes and it shrinks once (drying shrinkage); then firing it in the kiln at around 1000°C fuses the clay particles together more tightly (sintering), causing a second round of shrinkage (firing shrinkage). The shrinkage rate you enter into this tool is the ratio between the size after bisque firing and the size after the final firing — not the size right after forming — so it's worth being careful not to confuse the two.

Good to know for real-world shrinkage calculations

Shrinkage varies by clay body, so when using a new clay for the first time, checking the manufacturer's spec sheet or firing a test tile and measuring it directly gives the most accurate number
Even the same clay can shrink differently depending on the kiln's firing temperature (cone number), so check the rate for the temperature you actually fire at
Width, depth, and height don't always shrink at exactly the same rate — wheel-thrown pieces in particular can shrink slightly differently by direction, so measuring and correcting for critical work is worth the extra step
For pieces that need a precise fit (like a lidded jar set), it's safer to build in a bit of extra margin beyond the calculated value

Frequently Asked Questions

Does this only account for shrinkage between bisque and final, or the whole process from wet clay?: It applies your entered shrinkage rate (%) directly between the bisque size and the final size fields. If you know the total shrinkage rate from the wet/forming stage instead, you can enter your forming size into the bisque field and use it the same way.
What happens if both sides already have values and I change one?: The field you just edited becomes the new reference, and the opposite field recalculates and updates automatically.
What's a typical clay shrinkage rate?: It varies by clay body, but it's generally around 5-15%, with some kaolin-heavy or porcelain bodies shrinking as much as 15-20%. Check your clay manufacturer's spec sheet or run a test firing for the most accurate number.
Should the shrinkage rate include shrinkage from before bisque firing (right after forming)?: No — the shrinkage rate here is based on the bisque size. If you know the total shrinkage from right after forming all the way to the final firing, you can use that by entering the as-formed size in the "bisque size" field instead.
Can I calculate just one of width, depth, or height?: Yes, each dimension is calculated independently, so you only need to enter the ones you need.
Could the shrinkage rate be negative or over 100%?: No, clay shrinkage is always a positive value between 0 and 100%. The typical range is around 5-20%.

Clay Shrinkage Calculator

Bisque size

Final (glaze-fired) size