What is Clay?
Clay is a form of soil made up of tiny particles of aluminum silicate. When moist, clay is malleable, and when it dries, it becomes hard and brittle — you cannot mold it anymore. Clay is widely used as a material for bricks, tiles, and pottery.
Clay Shrinkage Definition
When making pottery, remember that the final size will differ from what you've sculpted — it will be smaller. This is the clay shrinkage phenomenon.
Clay shrinkage is the process of shrinking that occurs as the clay dries out. While drying, water particles evaporate from the original mass and the whole object becomes smaller. Clay shrinkage applies to all types of clay — regular clay, metal clay, and air-dry clay.
- Regular clay will shrink by 10%–20%.
- Air-dry clay has the narrowest range — the object will get 8%–12% smaller.
- Metal clay shrinkage strongly depends on the type and varies from 5% to 30%.
How to Use the Clay Shrinkage Calculator
- Measure your clay object before it dries out — you need all three dimensions: height, width, and length.
- Select your unit system (metric: cm, or imperial: inches).
- Choose your clay type from the dropdown to auto-fill the shrinkage percentage, or enter it manually.
- Click Calculate and let the calculator compute the final dimensions for you.
Calculating Clay Shrinkage — Formula
If you want to estimate the final dimensions on your own, use this formula:
final dimension = original dimension × (1 − CS / 100)
Where:
- final dimension — Length, width, or height of your object after curing.
- original dimension — The measured value before curing.
- CS — Clay shrinkage percentage (e.g., 15 for 15%).
Example: If your piece is 10 cm long and you're using a clay with 14% shrinkage:
final length = 10 × (1 − 14/100) = 10 × 0.86 = 8.6 cm
What is Metal Clay?
Metal clay consists of fine metal particles (silver, gold, bronze, copper) combined with water and an organic binder. It is used primarily to make jewelry. When you fire metal clay objects in a kiln, the binder burns away, leaving pure, sintered metal particles.
Metal clay jewelry will shrink while burned — the level of shrinkage depends on the material used.
Metal Clay Shrinkage Chart
| Clay Type | Shrinkage | Notes |
|---|---|---|
| Regular clay (low) | 10% | Earthenware, stoneware |
| Regular clay (mid) | 15% | Average pottery clay |
| Regular clay (high) | 20% | High-shrinkage stoneware |
| Air-dry clay | 8%–12% | No firing needed |
| PMC3 (Fine Silver) | 12% | Precious Metal Clay |
| PMC+ (Fine Silver) | 12% | Precious Metal Clay |
| PMC Standard | 28%–30% | Original formulation |
| BRONZclay | 20% | Bronze metal clay |
| COPPRclay | 15% | Copper metal clay |
| Hadar's Copper | ~15% | Varies by formula |
| Metal clay (max) | 30% | Some specialty types |
FAQs
How do I calculate 14 percent shrinkage on clay?
Multiply each dimension by (1 − 14/100) = 0.86. For example, a 10 cm length becomes 10 × 0.86 = 8.6 cm.
What material is used to reduce clay shrinkage?
Grog (pre-fired clay particles) is the most common additive used to reduce shrinkage. Sand, silica, and non-plastic fillers also help reduce shrinkage by replacing plastic clay with non-shrinking materials.
Does air-dry clay shrink less than kiln-fired clay?
Air-dry clay typically has the narrowest shrinkage range (8%–12%), while high-fire stoneware can shrink up to 20% and some metal clays can shrink up to 30%.
Why does clay shrink?
During drying and firing, water molecules evaporate and the clay particles move closer together. In metal clays, the organic binder also burns away, which contributes to additional shrinkage.