Clay Shrinkage Calculator

Find how big to throw or build a piece so it fires to the size you want, or measure your own clay's shrinkage from a test tile.

Mode & clay shrinkage %

Clay body:

Shrinkage sourcePreset, test tile, or custom %Shrinkage %Wet to fired total shrinkageI know theWhich size you are starting fromMeasurement unitsApplies to piece dimensions

Piece dimensions & test tile

Quick start:

Diameter or lengthFired diameter or length you wantHeightOptional piece heightDepth or widthOptional 3rd dimension (tiles/slabs)Capacity (fl oz)Optional volume (shrinks ~3×)

You typeWe calculate

How it's calculated

Shrinkage % = (wet − fired) ÷ wet × 100
Wet size    = fired size ÷ (1 − shrinkage)
Fired size  = wet size × (1 − shrinkage)
Capacity    = (1 − shrinkage)³

Shrinkage is measured against the wet length. Volume shrinks about three times as much as size.

Sources and worked example

Make it this big wet11.36 inTo fire to 10.0 in at 12% shrinkage

×1.136 throw factor

Throw / Wet size → Fired size (12% shrinkage):Diameter / length: 11.36 in wet → 10.00 in fired · Height: 1.42 in wet → 1.25 in fired. Because clay shrinks in all 3 dimensions, volume shrinks by 31.9% (multiply desired fired volume by 1.47× when throwing).

Wet size11.36 in

Fired size10.00 in

Multiply fired size by1.136

Capacity lost31.9%

Wet sizes for your dimensions and common fired sizes
Dimension / Reference	Throw / Wet size	Fired size
Your diameter / length	11.36 in	10.00 in
Your height	1.42 in	1.25 in
2 in reference	2.27 in	2 in
3 in reference	3.41 in	3 in
4 in reference	4.55 in	4 in
5 in reference	5.68 in	5 in
6 in reference	6.82 in	6 in
8 in reference	9.09 in	8 in
10 in reference	11.36 in	10 in
12 in reference	13.64 in	12 in

Pricing & tracking your pottery studio:Once your pieces come out of the kiln at 12% shrinkage, pricing them means adding clay weight, glaze batch cost, kiln electricity + element wear, and throwing/trimming time. The Pottery Studio Spreadsheet calculates retail, wholesale and consignment prices per piece, logs kiln firings, scales glaze recipes, and tracks craft show ROI.

Do you sell your pottery, or plan to?

The full template

Selling your pottery? Price every piece from what it really costs

Pricing Calculator adds clay, glaze, firing, labor and overhead into retail, wholesale and consignment prices
Kiln Firing Log works out the cost per firing and per piece, with element wear
Glaze Recipes scale any batch and cost it from your own raw-material prices
Sales Log, craft show ROI and consignment tracking, with fees, COGS and profit

Pottery Studio Spreadsheet$19.99One-time · instant downloadExcel + Google Sheets + PDF guide5.0 shop rating on Etsy

How clay shrinkage works

Clay shrinks twice. It shrinks as the water dries out, then again in the kiln as it matures. A piece you throw or build at one size comes out of the final firing smaller in every direction. To end up with the size you want, you make it bigger by the right amount.

1. Measure your clay with a test tile

Roll a slab or tile, and press two marks exactly 10 cm apart while it is wet, the way Digitalfire's shrinkage test does. Let it dry, fire it to your usual final cone, and measure again. Shrinkage is the change divided by the wet length: (wet − fired) ÷ wet × 100. With a 10 cm line it is simply 100 minus the fired length in millimeters: 88 mm means 12%. If you measure it bone dry too, you also get drying and firing shrinkage separately.

2. Size the piece: divide by (1 − shrinkage)

The fired piece keeps (1 − shrinkage) of its wet size. At 12% it keeps 88%, so the wet size is the fired size divided by 0.88. Ceramic Arts Network gives the same rule in fractions: at 12.5% the clay keeps 7/8 of its size, so divide the fired size by 7 and multiply by 8. Adding the percentage to the fired size instead comes out a little small, because the extra clay shrinks too.

3. Allow for capacity

A pot shrinks in height and width at once, so what it holds shrinks with the cube: (1 − shrinkage)³. At 12% a mug keeps only 68.1% of its wet volume. Plan mugs, bowls and lidded jars from the volume, not just the width.

Typical shrinkage by clay type

These ranges combine Digitalfire's typical drying shrinkage (about 5 to 7% for plastic clays) with its typical firing shrinkage for each type. Your clay's data sheet, or better a test tile, beats any table.

Typical total shrinkage by clay type
Clay	Drying	Firing	Total, wet to fired
Earthenware (low fire)	5 to 7%	3 to 4%	7.9 to 10.7%
Stoneware (mid or high fire)	6 to 7%	5 to 6%	10.7 to 12.6%
Porcelain	6 to 7%	7 to 8%	12.6 to 14.4%

Drying and firing do not simply add up. Firing shrinkage is measured from the dry length, which is already smaller, so the total is 1 − (1 − drying) × (1 − firing). Digitalfire's example: 6.25% drying plus 6.66% firing adds to 12.9%, but the real total is 12.5%.

Worked example

A potter marks a 10 cm line on a test tile. Bone dry it measures 9.4 cm, and after the glaze firing 8.8 cm.

Worked example
Drying: (10 − 9.4) ÷ 10	6.0%
Firing: (9.4 − 8.8) ÷ 9.4	6.4%
Total: (10 − 8.8) ÷ 10	12.0%
Mug 3.5 in wide fired: 3.5 ÷ 0.88	3.98 in wet
To hold 12 oz fired: 12 ÷ 0.88³	17.6 oz wet

The clay shrinks 12.0% overall. To get a 3.5 inch mug, the potter throws it 3.98 inches wide. It also needs to hold about 17.6 ounces wet to hold 12 after firing, because it loses 31.9% of its volume.

Where the sources differ

Some potters measure firing shrinkage from the dry length and others from the wet length, so check which one a data sheet means. Digitalfire bases drying shrinkage on the wet length and firing shrinkage on the dry length. For sizing a piece, the total from wet to fired is the number you need.

Published "typical" figures vary. Ceramic Arts Network says most stoneware shrinks around 12.5%, and Laguna's B-Mix 5 data lists 12% at cone 5, while the Digitalfire ranges above work out to 10.7 to 12.6%. That gap matters on big pieces: Ceramic Arts Network's 11 inch plate is 12.57 inches wet at 12.5%, but 12.36 inches at 11%. Digitalfire treats firing shrinkage as a sign of how far the clay has vitrified, so firing hotter than usual shrinks it more and firing cooler shrinks it less.

Sources

FAQ

Common questions

How much does clay shrink when fired?

Most pottery clays shrink about 10% to 13% from wet to fired, and some porcelains up to about 15%. Earthenware fired at low temperatures usually shrinks less, around 8% to 11%. The exact number depends on the clay body and how hot you fire it, so test your own clay.

How do I calculate clay shrinkage?

Mark a line of known length on a wet slab or test tile, such as 10 cm. Let it dry, fire it to the temperature you will use, and measure the line again. Shrinkage % = (wet length − fired length) ÷ wet length × 100. A 10 cm line that fires to 8.8 cm shrank 12%.

How big should I make a piece to allow for shrinkage?

Divide the fired size you want by (1 − shrinkage). At 12%, divide by 0.88: a 10 inch plate needs to be about 11.36 inches wet. Do not just add 12% to the fired size. That comes out a little small, because the extra clay shrinks too.

Does clay shrink more in volume than in size?

Yes. Shrinkage happens in every direction, so a pot that shrinks 12% in height and width loses about 32% of its volume. If a mug needs to hold 12 ounces after firing, make it hold about 17.6 ounces wet.

What is the difference between drying and firing shrinkage?

Drying shrinkage happens as water leaves the clay, from wet to bone dry; a typical plastic pottery clay shrinks about 6%. Firing shrinkage happens in the kiln as the clay matures, and is bigger the more the clay vitrifies. To size a piece you need the total from wet to fired, so measure your test tile after the final firing at your usual cone.

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