---
title: "Clay Shrinkage Calculator & Ruler | Ceramic Drift"
description: "Work out clay shrinkage from a test tile, the size to throw for a fired size or the fired size of a thrown pot, volume shrinkage, and a ruler to print."
url: https://ceramicdrift.me/clay-shrinkage-calculator/
---

Wet to fired, both ways

# Clay shrinkage calculator

Shrinkage is (wet length − fired length) ÷ wet length × 100. Mark 100 mm on a wet test tile; if the marks are 87.5 mm apart after firing, your clay shrinks 12.5%, and a mug you want 90 mm tall should be thrown 102.9 mm tall.

## How to measure your clay's shrinkage

Roll a test tile of the clay you will use, press two marks exactly 100 mm (or 4 in) apart while it is wet, then measure again when it is dry and after the glaze firing. Fire it to the cone you will use, because clay shrinks more the closer it gets to maturity.

- **Size to make** divides each fired size by 1 − shrinkage. **Fired size** multiplies by it.
- **Volume shrinkage** is 1 − (1 − s)³, assuming the clay shrinks the same amount in every direction. At 12.5% linear, a mug loses about a third of its capacity.
- **Drying and firing shrinkage don't add up** to the total, because firing shrinkage is measured on the dry length. Digitalfire's example: 6.25% plus 6.66% looks like 12.9%, but the total is 12.5%.

## Sources

- Shrinkage measured on the wet (plastic) length: [Digitalfire, Drying Shrinkage](https://digitalfire.com/glossary/drying+shrinkage); fired shrinkage on the dry length: [Digitalfire, SHAB shrinkage and absorption test](https://digitalfire.com/test/shab); the 6.25% + 6.66% example: [Digitalfire, “Drying shrinkage + firing shrinkage ≠ total shrinkage”](https://digitalfire.com/picture/2239).
- Example clay body: [Plainsman Clays, M370](https://www.plainsmanclays.com/product/m370-2/) (dry 5.5–6.9%, fired 6.0–7.4% at cone 6, checked 2 November 2026). The total range is our sum by Digitalfire's method. Your clay's data sheet will differ.
- Volume shrinkage, 1 − (1 − s)³, is the cube of the linear factor for a clay that shrinks evenly in all directions. 1 in = 25.4 mm and 1 US fl oz = 29.5735 mL: [NIST Guide to the SI, Appendix B.8](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8).

## Questions

**How do I calculate clay shrinkage?**

Shrinkage % = (wet length − fired length) ÷ wet length × 100. Marks 100 mm apart that fire to 88 mm mean 12% shrinkage.

**How big should I throw a mug?**

Divide the fired size you want by 1 − shrinkage. With 12% shrinkage, a mug that should be 90 mm tall after firing is thrown 90 ÷ 0.88 = 102.3 mm tall.

**How much does a pot's capacity shrink?**

Capacity shrinks with the cube of the linear factor. At 12.5% linear shrinkage, 0.875³ is about 0.67, so a pot that held 450 mL wet holds about 300 mL fired.