Clay shrinkage is the reduction in size that occurs during the drying and firing process. As water evaporates from wet clay during drying, clay particles move closer together, causing the piece to shrink. During firing, chemical changes and vitrification cause additional shrinkage.

Understanding your clay's shrinkage rate is essential for creating pieces with precise final dimensions. Different clay bodies have different shrinkage rates, typically ranging from 8% to 15%. Porcelain usually shrinks more (12-15%) than stoneware (10-13%) or earthenware (8-10%).

Shrinkage occurs in two main stages: drying shrinkage (plastic to bone dry) accounts for about 40-50% of total shrinkage, while firing shrinkage (bone dry to fired) accounts for the remaining 50-60%. The higher the firing temperature, the greater the firing shrinkage.

Step 1: Select your measurement system—Imperial (inches) or Metric (millimeters).

Step 2: Perform a shrinkage test by creating a test piece with your clay. Mark a precise measurement line (e.g., 100mm) on leather-hard clay and record this as the "Initial Wet Size."

Step 3: Fire the test piece at your intended cone/temperature. After firing and cooling completely, measure the same line and enter it as "Final Fired Size."

Step 4: The calculator displays your clay's linear shrinkage percentage and volume shrinkage.

Step 5: Enter your desired final dimension in "Target Finished Size" to calculate how large your wet piece needs to be to achieve that final size after firing.

Formula: Shrinkage % = ((Initial - Final) / Initial) × 100. Required Wet Size = Target Final / (1 - Shrinkage/100). Volume shrinkage ≈ (1 - (1 - Linear/100)³) × 100.