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Clay Shrinkage Calculator

Convert between wet and fired dimensions, and see what a linear shrinkage does to the volume and the capacity.

Pottery & Clay
A pot made to 20 centimetres on the wheel does not fire to 20 centimetres. Clay shrinks as it dries and again in the firing, typically 5 to 12 percent in each direction, and because it shrinks in all three dimensions the volume falls by far more than the linear figure suggests. This calculator converts between wet and fired dimensions in both directions, and reports what the shrinkage does to the capacity of the piece.

At a glance

What you enter
Which direction are you converting?, Linear shrinkage from wet to fired, Wet diameter, Wet height, Measured fired diameter, Wall thickness
What you get
Fired diameter, Fired height, Wet size needed for a target fired size, Dimension factor, Volume remaining after firing, Volume at the wet dimensions, Volume at the fired dimensions, Volume the shrinkage removed, Share of the volume removed by shrinkage, Interior diameter, Interior height, Interior capacity, The shrinkage your measurement implies, Your measurement against the figure used here
Formula shown
Yes, every step, right below your results.
Cost and privacy
Free, no account needed, and nothing you type is stored.

See worked examples ↓ Read the FAQ ↓ Share this calculator ↓

Which direction are you converting?

The third option works out the shrinkage of a piece you have already fired, which is how you find your own figure.

Five to twelve percent is typical. Seven percent is a common stoneware mid range figure.

The dimension as it comes off the wheel or out of the mould.

Only used by the comparison option, to work out the shrinkage you actually got.

Used for the interior capacity. The wall thickness shrinks with the pot, so it is quoted fired here.

Reset

Results are estimates for general information only, always verify with a professional or official source before acting on them.

How to use the Clay Shrinkage Calculator

  1. 1 Enter Which direction are you converting?, The third option works out the shrinkage of a piece you have already fired, which is how you find your own figure.
  2. 2 Enter Linear shrinkage from wet to fired (%), Five to twelve percent is typical. Seven percent is a common stoneware mid range figure.
  3. 3 Enter Wet diameter (cm), The dimension as it comes off the wheel or out of the mould.
  4. 4 Enter Wet height (cm)
  5. 5 Enter Measured fired diameter (cm), Only used by the comparison option, to work out the shrinkage you actually got.
  6. 6 Enter Wall thickness (mm), Used for the interior capacity. The wall thickness shrinks with the pot, so it is quoted fired here.
  7. 7 Press Calculate. You get Fired diameter, Fired height, Wet size needed for a target fired size, Dimension factor, Volume remaining after firing, Volume at the wet dimensions, Volume at the fired dimensions, Volume the shrinkage removed, Share of the volume removed by shrinkage, Interior diameter, Interior height, Interior capacity, The shrinkage your measurement implies, Your measurement against the figure used here, and every intermediate step stays visible under "How is this calculated?"
  8. 8 Change one number at a time to see what moves the result, that is usually the most useful thing a calculator can tell you.

Worked examples

Real numbers run through this calculator. Open any example to load it into the form above and change it.

A 20 cm wet cylinder at 7 percent

A common stoneware body with a 7 mm wall.

You enter

Which direction are you converting?
1
Linear shrinkage from wet to fired
7%
Wet diameter
20 cm
Wet height
12 cm
Measured fired diameter
18.60 cm
Wall thickness
7 mm

You get

Fired diameter
18.60 cm
Fired height
11.16 cm
Wet size needed for a target fired size
20.00 cm
Dimension factor
0.93
Volume remaining after firing
80.4%
Volume at the wet dimensions
3.77 L
Volume at the fired dimensions
3.03 L
Volume the shrinkage removed
0.74 L
Share of the volume removed by shrinkage
19.6%
Interior diameter
17.20 cm
Interior height
10.46 cm
Interior capacity
2.43 L
The shrinkage your measurement implies
7.0%
Your measurement against the figure used here
0.0%

It fires to 18.6 cm across and 11.16 cm tall, holding about 3.03 litres by outer dimensions and 2.6 litres inside the wall. Twenty percent of the volume goes in the firing.

Open this example in the calculator →

Working back from a 20 cm fired target

The size to throw so the finished piece measures 20 cm.

You enter

Which direction are you converting?
2
Linear shrinkage from wet to fired
8%
Wet diameter
20 cm
Wet height
12 cm
Measured fired diameter
18.60 cm
Wall thickness
7 mm

You get

Fired diameter
20.00 cm
Fired height
11.04 cm
Wet size needed for a target fired size
20.22 cm
Dimension factor
0.92
Volume remaining after firing
77.9%
Volume at the wet dimensions
3.77 L
Volume at the fired dimensions
3.47 L
Volume the shrinkage removed
0.30 L
Share of the volume removed by shrinkage
8.0%
Interior diameter
18.60 cm
Interior height
10.34 cm
Interior capacity
2.81 L
The shrinkage your measurement implies
7.0%
Your measurement against the figure used here
-1.0%

At 8 percent shrink, a 20 cm fired diameter needs a wet diameter of 21.7 cm and a wet height of 13 cm. Throw oversize, not to the finished dimension.

Open this example in the calculator →

Checking a fired test piece

A bar marked at 100 mm that measures 92 mm after firing.

You enter

Which direction are you converting?
3
Linear shrinkage from wet to fired
7%
Wet diameter
20 cm
Wet height
12 cm
Measured fired diameter
18.40 cm
Wall thickness
7 mm

You get

Fired diameter
18.40 cm
Fired height
11.16 cm
Wet size needed for a target fired size
19.78 cm
Dimension factor
0.93
Volume remaining after firing
80.4%
Volume at the wet dimensions
3.77 L
Volume at the fired dimensions
2.97 L
Volume the shrinkage removed
0.80 L
Share of the volume removed by shrinkage
21.3%
Interior diameter
17.00 cm
Interior height
10.46 cm
Interior capacity
2.37 L
The shrinkage your measurement implies
8.0%
Your measurement against the figure used here
1.0%

The measurement implies 8 percent shrinkage against the 7 percent used here, so the whole calculation should be rerun with the measured figure.

Open this example in the calculator →

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Frequently asked questions

How much does clay shrink when fired?
Typically 5 to 12 percent linearly from wet to fired, with 7 percent a common mid range figure for stoneware. The shrinkage happens in two stages: about 5 to 7 percent as the clay dries, and another 2 to 4 percent in the firing as the body densifies. Porcelain often shrinks more, sometimes 12 percent or beyond, and a heavily grogged sculpture body shrinks less. The right figure for your work is the one you measure on your own test piece.
How do I work out the wet size for a fired size?
Divide the target fired size by one minus the shrinkage, not multiply. A 20 centimetre fired diameter at 7 percent shrinkage needs a wet diameter of 20 divided by 0.93, which is 21.5 centimetres. Multiplying instead gives 18.6, which is the wrong direction and produces a pot that fires undersized. This is the single most common arithmetic mistake in sizing work to a commission.
Why does shrinkage affect the volume so much?
Because it acts in all three dimensions at once. A 7 percent linear shrink leaves 93 percent in each direction, and 0.93 cubed is 0.804, so the fired piece holds about 20 percent less than its wet dimensions suggested. At 12 percent linear the volume factor is 0.68, so nearly a third of the capacity is gone. This is why a jug or a bowl can look right on the wheel and come out of the kiln smaller than the intended serving size.
How do I measure my own clay shrinkage?
Make a test bar or a small cylinder, mark two points exactly 100 millimetres apart with a needle while the clay is still soft, and fire it exactly the way you fire your work. Measure the marks again and the difference in millimetres is your shrinkage percentage. Do it for each body you use and repeat it if you change supplier, because the answer depends on the body, the water content, the forming method and the firing schedule together.
Does the wall thickness shrink too?
Yes, proportionally, so a 7.5 millimetre wall thrown wet fires to about 7 millimetres. That matters for capacity, because the interior is the outside dimension minus twice the fired wall thickness. On a small mug a 3 millimetre difference across the wall is a noticeable share of the volume, while on a large bowl it barely registers. Quote interior capacity from the fired interior dimensions rather than from the outside.

More money questions answered →

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