How Much Does Pottery Shrink When Fired?

Pottery shrinks roughly 8-15% from wet clay to finished, glaze-fired piece. Earthenware shrinks the least (around 4-8% total), stoneware typically lands at 10-12%, and porcelain shrinks the most at 12-15%.

That total happens in two stages: about half during drying, and the rest in the kiln as the clay matures. A mug I throw at 5 inches tall comes out of the glaze fire closer to 4.4 inches, which is why I always make pieces bigger than I want them to end up.

Why Clay Shrinks: The Two Stages

Clay shrinks twice, and for two different reasons.

Drying shrinkage (about 4-8%). Wet clay is full of water sitting between the clay particles. As that water evaporates, the particles pull closer together and the whole piece gets smaller. By the time a piece is bone dry, most of the drying shrinkage is done. That’s also why a piece can crack if one part dries faster than another. If you’re not sure when a piece is ready for the kiln, my post on whether pottery can be too dry to fire covers how to judge dryness.

Firing shrinkage (about 4-8% more). In the kiln, the remaining chemically bonded water burns off, and then at higher temperatures the clay particles begin to sinter and fuse. The closer a clay gets to full vitrification (that dense, glassy, watertight state), the more it tightens up and shrinks. This is why porcelain fired to cone 10 (about 2,345°F / 1,285°C) shrinks far more than a flowerpot fired to cone 04 (about 1,945°F / 1,063°C).

Fire the same clay hotter or hold it at temperature longer and you’ll get a little more shrinkage, because vitrification goes further. My guide on how hot a kiln needs to be for pottery breaks down the cone ranges for each clay type.

Shrinkage Rates by Clay Type

Every clay body shrinks differently, but these ranges hold for most commercial clays:

Clay type	Typical firing range	Total shrinkage (wet to glaze-fired)
Earthenware	Cone 06-04 (1,828-1,945°F / 998-1,063°C)	4-8%
Mid-fire stoneware	Cone 5-6 (2,167-2,232°F / 1,186-1,222°C)	10-12%
High-fire stoneware	Cone 9-10 (2,300-2,345°F / 1,260-1,285°C)	11-13%
Porcelain	Cone 6-10	12-15%
Heavily grogged sculpture clay	Varies	6-9%

Two things drive these differences:

• Particle size. Finer particles pack more water layers between them, so they shrink more as that water leaves. Porcelain has extremely fine particles, which is exactly why it shrinks the most. I explain what makes porcelain different in my post on what porcelain pottery is.
• Degree of vitrification. Earthenware never fully vitrifies, so it stops shrinking earlier. Vitreous stonewares and porcelains keep tightening right up to their top temperature.

Your clay’s bag or the manufacturer’s website almost always lists the shrinkage rate at a specific cone. Trust that number over any general chart. But verify it with a test bar, which I’ll show you below.

How Much Shrinkage Happens at Each Firing?

If you bisque fire and then glaze fire (the standard two-firing process), the shrinkage splits unevenly:

• Wet to bone dry: the biggest single chunk, typically 4-8%.
• Bisque firing (cone 06-04): very little, usually 1-2%. Bisque is deliberately fired low so the clay stays porous for glazing. More on that in my post on what bisque pottery is.
• Glaze firing (cone 6-10 for stoneware/porcelain): the rest, often 4-7%, as the clay vitrifies.

So a piece that measures 10 inches wet might be about 9.4 inches bone dry, 9.3 inches after bisque, and 8.8 inches after the glaze fire. The timing of all this matters too. A full firing cycle takes longer than most people expect, which I cover in how long pottery takes to fire.

How to Calculate Your Clay’s Shrinkage Rate

Don’t guess — test. This takes ten minutes and one extra spot in your next two firings:

1. Roll out a slab of your clay about 3/8 inch thick.
2. Cut a bar roughly 12 cm long and scribe two marks exactly 10 cm (100 mm) apart.
3. Let it dry flat, then measure the distance between the marks. If it’s 94 mm, your drying shrinkage is 6%.
4. Fire the bar through your normal bisque and glaze firings, measuring after each.
5. Final measurement of 88 mm means 12% total shrinkage.

The formula: (original length − fired length) ÷ original length × 100 = shrinkage %.

I keep a fired test bar for every clay body I use, labeled with the cone it was fired to. When a customer asks for a 10-inch platter, I check the bar and throw at 11.4 inches.

Designing Around Shrinkage

Once you know your rate, the math is simple. A few situations still deserve extra care:

• Sizing up: divide the target size by (1 − shrinkage rate). For a 6-inch finished bowl with 12% shrinkage clay: 6 ÷ 0.88 = 6.8 inches wet.
• Lids and galleries: make the lid and pot from the same clay on the same day, and dry and fire them together. Different drying schedules mean different fits.
• Sets: throw all the mugs in a set from the same batch of clay. Shrinkage can vary slightly between batches.
• Tiles and flat work: flat pieces show uneven shrinkage as warping. Dry them slowly between sheets of drywall or wareboards, flipping occasionally.
• Handles and attachments: join parts at the same moisture content. A wet handle on a leather-hard mug shrinks more than the mug and cracks at the join.

Does Salt Fired Pottery Shrink More?

Salt firing doesn’t add shrinkage by itself, but salt fired work shrinks near the top of the range because of when the salt goes in. Salt glazing happens at high stoneware temperatures, typically cone 9-10 (2,300-2,345°F / 1,260-1,285°C), when sodium vapor reacts with the silica in the clay surface to form that classic orange-peel glaze.

At those temperatures, the stoneware or porcelain body underneath is fully vitrifying, so expect 11-14% total shrinkage on most salt fired pieces. The salt vapor only affects the outer surface; the shrinkage comes entirely from the clay body and the high firing temperature.

If salt firing interests you, I’ve written a full explainer on what salt glaze pottery is, including why it’s done in dedicated kilns, since the sodium vapor permanently coats the kiln interior.

Can You Reduce Shrinkage?

You can’t eliminate shrinkage, but you can manage it:

• Use a grogged clay. Grog (pre-fired ground clay) and sand have already done their shrinking, so a heavily grogged body shrinks several points less than a smooth one. This is why sculpture and raku bodies are gritty.
• Choose a lower-fire clay. Earthenware at cone 04 shrinks roughly half as much as porcelain at cone 10.
• Don’t overfire. Firing past your clay’s maturity adds shrinkage, slumping, and bloating with no benefit.
• Dry evenly and slowly. This doesn’t reduce total shrinkage, but it prevents the cracks and warping that uneven shrinkage causes. Cover pieces loosely with plastic and keep them away from drafts and direct sun.
• Keep wall thickness consistent. Thick and thin sections of the same piece shrink at different speeds, and that stress is where cracks start.

What you should never do is try to “cheat” shrinkage by underfiring functional ware. An immature clay body stays porous and weak. Fire to the cone your clay is designed for.

FAQ

How much does pottery shrink from wet to fired?

Most pottery shrinks 8-15% total from wet clay to glaze-fired piece. Earthenware sits at the low end (4-8%), stoneware around 10-12%, and porcelain at the high end (12-15%). Check your specific clay’s data sheet and confirm with a test bar.

Does pottery shrink more in the bisque firing or the glaze firing?

The glaze firing, by a wide margin. Bisque firing at cone 06-04 only shrinks a piece 1-2% because the clay doesn’t vitrify at that temperature. The glaze firing at cone 6-10 drives most of the firing shrinkage as the clay body tightens and matures.

How much does salt fired pottery shrink?

Salt fired pottery typically shrinks 11-14% total, because salt glazing is done at high stoneware temperatures (cone 9-10) where the clay body fully vitrifies. The salt itself doesn’t cause shrinkage. It only forms the glaze surface.

How do I calculate shrinkage for my clay?

Scribe two marks exactly 100 mm apart on a test bar of your clay, then measure again after the glaze firing. The formula is (original − fired) ÷ original × 100. A bar that measures 89 mm after firing has 11% shrinkage.

Why did my piece crack while shrinking?

Uneven shrinkage. The usual culprits are a thick bottom with thin walls, a handle attached at a different moisture level than the pot, or one side drying faster than the other. Slow, even drying under loose plastic solves most of it.

Does clay shrink when it dries or only when it’s fired?

Both. Roughly half the total shrinkage happens during drying as water evaporates from between the clay particles, and the rest happens in the kiln as the clay sinters and vitrifies.