# Shrinkage ruler FAQ: percentage, stage, units, accuracy, and fit

Studio notes · Choosing a ruler

Short answers about choosing a clay shrinkage percentage, measuring stages, checking a scale and planning a fit, with links when you need more detail.

By Zoë · The Poodle Potter

Published 2026-09-20 · 3 min read

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## What does the percentage mean?

It is **linear shrinkage**: the loss of length as a percentage of the starting length, not the change in volume. For a hypothetical 12% wet-to-glaze-fired rate, a 10 cm wet length is expected to finish at 8.8 cm. That figure belongs to those stages and that clay and firing process, not every piece of pottery.

## Which percentage should I choose?

Start with your clay supplier’s figure, checking its measurement stages and firing conditions. For a close fit, test your own clay through the process you intend to use. “Stoneware” alone is not enough information to pick a rate. The [percentage-selection guide](https://potteryruler.com/guides/choosing-shrinkage-percentage) helps you work from a supplier’s number to a useful choice.

## Can I use the same rate on wet, dry and bisque clay?

Not automatically. Wet, leather-hard, bone-dry, bisque and glaze-fired are different starting or finishing points; bone-dry clay is still unfired. Applying a wet-to-glaze-fired rate to a bone-dry piece counts its drying shrinkage again. Use a rate measured between the stages you actually need; [stage-specific sizing](https://potteryruler.com/guides/stage-specific-pottery-sizing) explains both directions.

## How big should I make the wet clay?

Work backwards from your target by dividing by the fraction that remains. At the hypothetical 12% wet-to-glaze-fired rate above, a 10 cm glaze-fired target needs a wet length of **10 ÷ 0.88 ≈ 11.36 cm**. Simply adding 12% does not undo 12% shrinkage. A compensated ruler uses adjusted mark spacing to put that calculation into a physical scale.

## Centimetres or inches? How long is the ruler?

Choose the unit you use for your targets and templates; the shrinkage percentage does not change with the unit. PoodlePotter’s ruler has a physical length of **24 cm (9.45 in)**, with centimetre or inch options. Physical length is not the same as the largest finished-size reading on a compensated scale. A longer format is not confirmed.

## What if my rate is 9.5% or 12.5%?

The confirmed choices here are **whole-number rates from 10% to 18%**. Decimal rates and rates outside that range are not confirmed. Do not round just to suit the available ruler if the resulting size difference would spoil the fit; use your measured rate in a calculation with an ordinary ruler instead.

## How do I check that a shrinkage ruler is accurate?

Compare it with an ordinary ruler, but check what its labels represent first. On a scale labelled with expected glaze-fired lengths, the 10 cm mark for 12% wet-to-glaze-fired shrinkage should sit about **11.36 ordinary centimetres from its zero mark**, not 10 cm. Other layouts need their own instructions. For paper rulers, check print scaling too. The [calibration guide](https://potteryruler.com/guides/calibrating-shrinkage-rulers) covers checking several spans.

## Will the finished piece be exactly that size?

No. A correctly scaled ruler cannot make the clay or firing perfectly repeatable, or prevent warping. Moisture, forming, drying and firing conditions all matter. I’d treat the reading as a planning estimate and test a representative piece before relying on a tight fit. [Digitalfire’s shrinkage test method](https://digitalfire.com/test/shab) explains why consistent testing matters.

## Does every lid need to be made bigger?

No. A same-clay pot and lid made at comparable moisture states and fired alike often shrink together. Do not automatically enlarge only the lid by the full shrinkage allowance. For a replacement lid, if the old pot is staying as it is, only the new lid has shrinking to do. Leave clearance, meaning room for the lid to move freely, and account separately for glaze on fitting surfaces. See [making a lid that fits](https://potteryruler.com/guides/pottery-lids-that-fit).

## Can I order one here now?

Not yet. This is a shop preview: checkout is not connected, and the Buy button does not place an order or take payment.

A little testing now. Fewer surprises after the kiln.

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