# Pottery shrinkage ruler buying guide: preset, custom, long, metric, or imperial?

Studio notes · Choosing a ruler

Choose a pottery shrinkage ruler by percentage, units, usable reach and studio workflow, with a concise comparison and clear limits on current options.

By Zoë · The Poodle Potter

Published 2026-09-20 · 5 min read

[All guides](https://potteryruler.com/guides)

![Dark pottery and terracotta vessels displayed in a sunlit wooden interior](https://potteryruler.com/images/guides/studio-shelves.webp)

A ruler can have the right percentage and still be awkward for the pot you want to make. It might use different units from your templates, stop short of a platter, or put several scales beside the one you need.

I'd choose in this order: **the right shrinkage rate, familiar units, enough reach, then a format that suits the job.** “Custom”, “long” and “metric” describe different things; they aren't competing answers to the same question.

## Which features actually matter?

| Option | Useful when | Check before choosing |
| --- | --- | --- |
| Single preset percentage (%) | You regularly use one clay and firing process. | The rate matches your measured start and end stages, not just the clay's name. |
| Multiple preset percentages (%) | You switch between tested clay bodies or firing processes. | The set includes the rates you need, and each scale is easy to identify. |
| Custom percentage (%) | Your repeatable test result is not covered by the presets. | The maker accepts that exact rate; choosing from a menu is not necessarily a bespoke scale. |
| Metric (cm) or imperial (inches) | You want to work in the same units as your plans and other tools. | The actual divisions are readable enough for the dimensions you need to check. |
| Longer ruler | Your wet slab, diameter or height exceeds a shorter tool's reach. | Both the physical length and usable scale span, at your chosen percentage. |
| Ordinary ruler plus calculation | You make occasional sized pieces or need a dimension beyond a shrinkage ruler's range. | You record the calculated wet dimension clearly and don't compensate it a second time. |

## Buy the rate for the measurement, not the clay label

Here, shrinkage means **linear shrinkage: a reduction in length**, not volume. A useful percentage needs two stage labels. Wet-to-glaze-fired is not the same measurement as bone-dry-to-glaze-fired, and leather-hard clay has already lost some moisture. Bisque and glaze-fired dimensions need not be identical either.

Start with your supplier's data, checking what the number measures and the firing conditions behind it. For work where size matters, use tests of your clay with a consistent starting moisture state, forming method, drying process and intended firing schedule. [Digitalfire's shrinkage test](https://digitalfire.com/test/shab) measures drying and firing shrinkage separately, a useful reminder that an unlabelled percentage is incomplete information.

A whole-number preset may be entirely adequate. A more specific number is only useful if your testing supports it and the dimensional difference matters to your project. The [custom versus fixed-percentage comparison](https://potteryruler.com/guides/custom-versus-fixed-shrinkage-rulers) covers that decision in more detail; you don't need to settle it by buying the most elaborate option.

## Choose the units you already think in

If your drawings and measurements are in centimetres, I'd keep the ruler in centimetres too. If you plan in inches, an inch scale avoids a conversion every time you move between the drawing and the clay. Neither unit system makes the clay more predictable.

Look for a close-up of the scale, not just “metric” or “imperial” in the title. Can you distinguish the divisions? Are the percentage labels obvious? Don't assume a centimetre ruler has the particular subdivisions you want, or that an inch ruler uses your preferred fractions. Our [metric and imperial reading guide](https://potteryruler.com/guides/metric-imperial-shrinkage-rulers) explains the unit side without making assumptions about a manufacturer's markings.

## Check the wet span, not only the finished size

A **compensated scale** has its marks spaced to allow for shrinkage. Its largest number and the ruler's physical length are different specifications. On a scale that labels wet spans with their predicted fired lengths, a labelled distance occupies more physical space than the same number on an ordinary ruler.

For example, suppose repeated tests under your intended drying and firing conditions support **12% wet-to-glaze-fired shrinkage**. A **22 cm glaze-fired target** needs a wet span of:

**22 cm ÷ (1 − 12/100) = 25 cm wet.**

That span cannot fit along a 24 cm physical ruler in one placement, even though the finished target is shorter than 24 cm. Usable marked reach may be shorter still; check the scale endpoints rather than assuming the whole tool is graduated.

For an occasional oversized piece, calculating the wet dimension and marking it with a longer ordinary ruler or a full-size template may be enough. For repeated large work, compare longer tools by their actual usable span. The [long-ruler guide](https://potteryruler.com/guides/long-shrinkage-rulers) covers the practical alternatives to repeatedly moving a short ruler.

## Will it suit the way you make?

At the wheel, calipers can transfer a diameter without pressing a ruler into a soft rim. A shrinkage ruler helps relate that span to the intended later dimension; it doesn't replace the calipers. With slabs, you may prefer to calculate a wet template once and use the template for the batch. For quick checks of wet work, choose instructions that clearly explain how to read an estimated later size.

In either direction, check what the scale's numbers mean. A compensated “10” is not automatically an ordinary 10 cm or 10 inches. Good instructions should show how the same scale relates a wet span to its estimated later size, rather than leaving you to add or subtract a percentage again.

For fitted work, the ruler is only part of the plan. A replacement lid for an already-fired pot needs allowance for its own remaining shrinkage. A lid and pot made together from the same clay often shrink together instead. Clearance for movement and glaze is a separate consideration in either case; no ruler guarantees the fit. The [lid-fitting guide](https://potteryruler.com/guides/pottery-lids-that-fit) separates those jobs.

Material and readability deserve a look too. [DiamondCore describes its ruler as flexible plastic](https://diamondcoretools.com/products/shrink-ruler); [Hartley & Noble specifies flexible acrylic](https://hartleyandnoble.co.uk/product/clay-shrinkage-rulers/). I'd still want a close-up of the marks: the material name alone doesn't tell you whether they'll be easy to read beside wet clay. Check the care instructions, and consider whether you need flexibility or a firm straightedge. Don't assume a measuring ruler is also suitable as a cutting guide.

## What is confirmed for the PoodlePotter ruler?

The current specification is **24 cm (9.45 in) physical length**, with **centimetre or inch options** and **whole-number shrinkage rates from 10% through 18%**. Decimal rates, percentages outside that range and longer or custom-length formats are not confirmed.

See the [buy page](https://potteryruler.com/buy) for current ruler options, pricing, delivery costs and checkout availability.

A little testing now. Fewer surprises after the kiln.

[Explore the ruler options](https://potteryruler.com/buy)

[View this page on https://potteryruler.com/guides/shrinkage-ruler-buying-guide](https://potteryruler.com/guides/shrinkage-ruler-buying-guide)