Free Clay Shrinkage Calculator
Typical Shrinkage Rates
Regular clay: 10%–20% • Air dry clay: 8%–12%Metal clay: 5%–30% (varies by brand and type)
Enter your dimensions and clay shrinkage
to see the final size after drying
Understanding Clay Shrinkage and Using the Pottery Shrinkage Calculator
When you shape an object from clay—whether ceramic clay, metal clay, or air‑dry clay—the final size after drying will inevitably be smaller than your original creation. The Clay Shrinkage Calculator (a free online tool for pottery and clay drying) takes the guesswork out of this process. By entering your measured dimensions before drying and the appropriate shrinkage percentage, you immediately get the finished size. This article explains how shrinkage works, provides the key formula, and gives you the shrinkage rates for many common clays so you can use the calculator with confidence.
What Is Clay and Why Does It Shrink?
Clay is a natural soil material composed mainly of fine aluminum silicate particles. In its wet state, clay is malleable and can be formed into nearly any shape. As it dries (or is fired), water evaporates from the mass, causing the particles to draw closer together—this is clay shrinkage. Every type of clay behaves this way, but the amount of shrinkage varies widely depending on the clay’s composition and water content.
Shrinkage Rates by Clay Type
- Regular (pottery) clay generally shrinks 10–20%.
- Air‑dry clay falls in a tighter range of 8–12%.
- Metal clays (silver, gold, bronze, copper, etc.) show the greatest variation, from as little as 5% up to 30%, depending on the specific brand and formulation.
Knowing which category your clay belongs to helps you pick the correct shrinkage percentage for the calculator.
How to Use the Clay Shrinkage Calculator
- Measure your uncured object: record its length, width, and height (or diameter, if a cylinder).
- Enter the three dimensions into the calculator. The default unit is centimeters, but you can switch to inches or any other convenient unit.
- Input the clay shrinkage percentage (e.g., 14% for a typical mid‑range shrinkage). Use the values given in later sections if you are using a metal clay.
- Read the results: the tool instantly displays each final dimension after drying or firing.
That’s all there is to it—no manual math required.
The Shrinkage Formula
If you prefer to calculate by hand, the formula is straightforward:
where is the clay shrinkage percentage.
For example, to find the final length of a piece that originally measured with a shrinkage of :
Apply the same calculation to width and height.
Reducing Shrinkage with Grog
To counteract shrinkage, potters often mix grog (pre‑fired, ground clay) into their fresh clay. Because grog particles have already shrunk during their own firing, they act as a stable filler that reduces the overall contraction of the object as it dries. Adding grog is a common technique when you need to minimize size change.
Metal Clay Shrinkage Details
Metal clays are a blend of fine metal particles (silver, gold, bronze, copper, etc.), an organic binder, and water. When fired in a kiln, the binder burns away and the metal particles sinter together, forming a solid metal piece. The shrinkage during this process is often substantial and varies by product.
Below are the shrinkage ranges for the most common metal clay families. Use these figures as the value when using the calculator.
Brass-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Aussie brass (pink, vintage) | 12–15% |
| Goldie lemon brass | 9–15% |
Bronze-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Aussie bronze (Antarctic Moonlight/Sand, Desert Sun, Gold/Ruby, Iron Bark) | 12–15% |
| Five Star Bronze (Regular, Light, Red, White) | 12–15% |
| Goldie Bronze (Hard/Soft/Mid) | 8–11% |
| Goldie de la Rosa Bronze | 14–19% |
| Goldie Roman Bronze | 10–12% |
| Goldie Sculptor’s Bronze | 9–14% |
| Goldie Snow Bronze | 16–30% |
| Hadar’s Clay | 25% |
| Hadar’s Quick‑Fire Clay | 10% |
| Hadar’s One‑Fire Bronze (also Brilliant Bronze) | 15% |
| Hadar’s One‑Fire Champagne/Dark Champagne Bronze | 30% |
| Hadar’s One‑Fire Rose Bronze | 25% |
| Hadar’s One‑Fire Smart Bronze | 24% |
| Hadar’s Quick‑Fire Brilliant/Rose Bronze | 25% |
| Metal Adventures BronzClay | 17–20% |
| Metal Adventures FASTfire BronzClay | 17–20% |
| MetalMania Metal Clay | 15–19% |
| Prometheus (Regular, Sunny) | 12–13% |
| Prometheus Jeweller’s Light Yellow | 17–19% |
| Prometheus Jeweller’s Greenish Yellow | 13–14% |
| Prometheus Jeweller’s Sterling White | 15–16% |
| Prometheus White Bronze | 10–12% |
Copper-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Art Clay (Copper) | 10% |
| Aussie / Aussie Snow White Copper | 12–15% |
| Cool Tool Cyprus Copper | 20% |
| Goldie Copper | 12–18% |
| Goldie Sculptor’s Copper | 15–23% |
| Hadar’s One‑Fire Copper | 25% |
| Hadar’s Quick‑Fire Copper | 25% |
| Metal Adventures COPPRclay | 20–22% |
| Metal Adventures White COPPRclay | 20–25% |
| Metal Mania Copper Clay | 15–19% |
| Prometheus Copper Clay | 9–10% |
Gold-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Art Clay (Gold) | 15% |
| Mitsubishi Materials PMC (Gold) | 11% |
Iron-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Goldie Cherry Iron | 9–17% |
| Goldie Red Iron | 12–18% |
| Goldie Sunset Iron | 8–16% |
| Goldie White Iron | 5–11% |
| Goldie Yellow Iron | 5–14% |
Platinum-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Mitsubishi Materials PMC (Platinum) | 20–30% |
Silver-Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Aussie .999/.960 Silver Clay | 10–12% |
| Aussie .999/.960 Silver Clay Super Flex | 12–15% |
| Art Clay (Silver) new formula | 8–9% |
| Art Clay (Silver) Standard and Slow‑Dry | 8–10% |
| Art Clay 650 Low Fire and Slow‑Dry | 8–9% |
| Art Clay Lite | 10% |
| Metal Magic Silver | 20–25% |
| Mitsubishi Materials PMC Flex | 10–12% |
| Mitsubishi Materials PMC Original/Classic | 25–30% |
| Mitsubishi Materials PMC+ lump | 12–15% |
| Mitsubishi Materials PMC+ sheet | 10–12% |
| Mitsubishi Materials PMC3 | 15–20% |
| Prometheus Silver Clay 950 | 15% |
| Prometheus Silver Clay 999 | 12–13% |
| Silver Smiths’ Metal Clay Powder | 10% |
Sterling Silver–Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Cool Tools EZ960 Sterling Silver | 10–11% |
| Metal Magic Sterling Silver | 25% |
| Mitsubishi Materials OneFire Sterling PMC | 13–16% |
| Mitsubishi Materials PMC Sterling | 15–20% |
Steel‑Based Metal Clays
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Hadar’s Clay One‑Fire Steel XT / Pearl Gray Steel | 25–30% |
| Hadar’s Clay | 10–15% |
Stainless Steel–Based Metal Clay
| Brand / Clay Type | Shrinkage Rate |
|---|---|
| Hadar’s Clay / Quick‑fire Hadar’s Clay | 10% |
For any clay not listed here, you can usually find the shrinkage percentage on the manufacturer’s product page. When in doubt, start with the midpoint of the range and adjust based on test pieces.
By combining the calculator with the shrinkage data above, you can plan your projects with confidence, knowing that your final dimensions will match your design intent.
FAQ
1. How do I calculate the final size of a clay piece if I know the shrinkage percentage?
Use the formula: final dimension = original dimension × (1 - CS/100), where CS is the shrinkage percentage. Alternatively, simply enter your original dimensions and the CS value into the clay shrinkage calculator to get instant results for all three dimensions.
2. What is the shrinkage range for typical metal clays?
Metal clays vary widely: silver clays often shrink 8–30% depending on the brand, bronze clays range from 8–30%, copper clays from 9–25%, and gold clays around 11–15%. Always check the manufacturer’s data for the specific product you are using.
3. Can I reduce the amount of shrinkage in my clay project?
Yes, by adding grog (pre‑fired, ground clay) to your fresh clay. The grog particles have already shrunk during their own firing, so they act as a stable filler and reduce the overall contraction of the piece as it dries.
4. How much does regular pottery clay shrink compared to air‑dry clay?
Regular (pottery) clay typically shrinks 10–20%, while air‑dry clay contracts less, with a typical range of 8–12%. However, the exact amount still depends on the specific product and moisture content.
5. Do I need to measure my object in centimeters for the calculator?
No, the calculator allows you to choose any convenient unit (centimeters, inches, etc.). Just ensure you use the same unit for all three dimensions, and the tool will output the final dimensions in that same unit.
How to Use
- Measure your clay object before it dries and enter the length, width, and height in the fields below.
- Enter the clay shrinkage percentage. Regular clay shrinks 10%-20%, air dry clay 8%-12%, and metal clay varies by type.
- View the calculated final dimensions after drying, shown alongside your original measurements.