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Clay Body Preset

Unit cm in mm

Wet (Plastic) Length Scored reference mark on wet piece

Bone-Dry Length Same mark after complete drying

Fired Length Same mark after glaze firing

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About

Clay shrinks twice: once as water evaporates during drying, and again as silica particles vitrify during firing. Total linear shrinkage for most stoneware bodies falls between 10% and 15%, but the exact value depends on clay mineralogy, particle size distribution, water content, and peak firing temperature (cone). Misjudging shrinkage by even 2% on a 30cm piece means your lid won't fit, your tiles won't align, and your production run is scrap. This calculator uses the standard test-bar method: measure a scored line on the wet piece, re-measure after bisque and after glaze firing, and compute drying, firing, and total linear shrinkage. It also approximates volumetric shrinkage from linear data.

The reverse-sizing mode solves the inverse problem: given a desired finished dimension, it computes the required wet dimension so the piece fires to spec. Eight common clay body presets supply typical shrinkage ranges, but you should always run your own test tiles - batch-to-batch variation, kiln atmosphere, and soak time all shift the number. This tool approximates shrinkage assuming uniform, isotropic contraction; anisotropy from throwing rings or slab rolling direction is not modeled.

Formulas

Linear shrinkage is the standard metric for ceramic production. The ASTM C326 test-bar method defines it as the percentage change in a scored reference length.

S_drying = L_wet − L_dryL_wet × 100

S_firing = L_dry − L_firedL_dry × 100

S_total = L_wet − L_firedL_wet × 100

Volumetric shrinkage is approximated from linear shrinkage assuming isotropic contraction:

S_vol = (1 − (1 − S_total100)³) × 100

To reverse-calculate the wet size required to achieve a desired fired dimension:

L_wet = L_desired1 − S_total100

Where L_wet = wet (plastic) length, L_dry = bone-dry length, L_fired = fired length, S = shrinkage percentage, and L_desired = target finished dimension.

Reference Data

Clay Body	Type	Cone Range	Drying Shrinkage	Firing Shrinkage	Total Shrinkage	Absorption
Earthenware (red)	Low-fire	06-02	5 - 7%	1 - 3%	6 - 10%	8 - 15%
White Earthenware	Low-fire	06-02	5 - 6%	2 - 4%	7 - 10%	6 - 12%
Buff Stoneware	Mid-fire	4-6	5 - 7%	4 - 6%	10 - 13%	2 - 5%
Dark Stoneware	High-fire	8-10	6 - 7%	5 - 7%	11 - 14%	1 - 3%
Porcelain (cone 6)	Mid-fire	5-6	5 - 6%	6 - 8%	11 - 14%	0.5 - 2%
Porcelain (cone 10)	High-fire	9-10	5 - 7%	7 - 9%	12 - 16%	0 - 1%
Raku Body	Low-fire	06-04	4 - 6%	1 - 3%	5 - 9%	10 - 18%
Paper Clay	Variable	06-10	3 - 5%	3 - 6%	6 - 11%	5 - 15%
B-Mix (Laguna)	Mid-fire	5-6	5 - 6%	5 - 7%	11 - 13%	1 - 3%
Terracotta (Italian)	Low-fire	06-01	5 - 7%	1 - 2%	6 - 9%	10 - 18%
Bone China	High-fire	6-9	4 - 6%	8 - 12%	12 - 18%	0 - 0.5%
Fireclay / Sculpture	High-fire	6-10	4 - 6%	3 - 5%	7 - 11%	3 - 8%

Frequently Asked Questions

Manufacturer specs are measured under controlled lab conditions: specific water content, standard bar thickness, exact ramp/soak schedule. In practice, your wedging intensity, slab thickness, drying speed, kiln loading density, and whether you fire in oxidation vs. reduction all shift the result by 1-3%. Always run your own test tiles using the same forming method and kiln program you plan to use in production.

Higher cone = more vitrification = more firing shrinkage. For example, a mid-fire stoneware at cone 6 may show 5% firing shrinkage, but the same body pushed to cone 8 could reach 7-8%. Over-firing causes bloating and can actually increase dimensions slightly before the piece deforms. Under-firing leaves the body porous with less shrinkage but higher water absorption.

No. The relationship is non-linear. For a cube with linear shrinkage S%, the volumetric shrinkage is (1 − (1 − S/100)³) × 100. At 12% linear shrinkage, volumetric shrinkage is approximately 31.8%, not 36%. The cubic relationship means small errors in linear measurement compound significantly in volume estimates.

Yes. Wheel-thrown pieces exhibit anisotropic shrinkage because clay particles align tangentially during throwing. Radial shrinkage can exceed axial shrinkage by 1-2%. Slab-rolled pieces shrink more across the rolling direction. Slip-cast pieces tend toward more isotropic shrinkage. This calculator assumes isotropic contraction; add a 1-2% safety margin for thrown work.

Roll or extrude a bar approximately 15 cm × 2.5 cm × 1 cm. While plastic, score two lines exactly 10.0 cm apart using a needle tool and ruler. Measure with digital calipers (not a tape measure) at the scored marks after each stage: wet, bone-dry, bisque-fired, and glaze-fired. Always measure the same pair of marks. Run at least three bars and average the results.

Yes. Non-plastic additives (grog, sand, molochite) act as a rigid skeleton that resists contraction. Adding 15-20% grog by weight can reduce total shrinkage by 2-4 percentage points. The tradeoff is reduced plasticity and a rougher surface texture. Paper fiber (in paper clay) also reduces drying shrinkage significantly by creating micro-channels that allow more uniform moisture escape.

For architectural tiles, a 1% error on a 30 cm tile means 3 mm per tile. Over a 3-meter wall with 10 tiles, that compounds to 3 cm of cumulative error. Grout joints cannot absorb that. Tiles will either leave visible gaps (under-estimated) or physically cannot fit (over-estimated). Production tile manufacturers test every new batch and adjust die sizes accordingly.