Calculate Thrown Clay Dimensions to Hit Target Fired Sizes — Free
Clay shrinks from wet wheel to final glaze firing, and dividing by one minus shrinkage is not the same as adding that percentage back. Compute the exact wet throwing dimension and check that it fits inside your kiln shelf clearance.
The proof surface
Paint-mix tools split liquid volumes by ratio. This divides target fired ceramic dimensions by the retained fraction after clay shrinkage and checks the wet piece against kiln shelf limits.
Why the flat version breaks
Adding shrinkage percent instead of dividing
Multiplying 102 mm by 1.15 gives 117.3 mm, which shrinks to 99.7 mm and misses the target fit.
Using bisque shrinkage for glaze-fired work
High-fire stoneware and porcelain shrink substantially more between bisque and vitrification.
Checking fired size against kiln shelves
Greenware and bisqueware enter the kiln larger than the final fired piece.
How to work the kiln firing docket
Measure the target height, rim diameter or lid seat size the finished piece must reach after glaze firing.
Enter total wet-to-fired shrinkage percentage from your test bars. A 102 mm mug in a 15 percent shrinkage clay must be thrown at 102 divided by 0.85, which is 120 mm — not 102 plus 15 percent.
Enter the maximum height or diameter your kiln furniture setup accommodates.
The summary reports the largest wet size across pieces and flags any piece that exceeds your kiln clearance — the 238 mm porcelain platter needs 280 mm wet, exceeding a 260 mm shelf setting.
What the kiln firing docket replaces
| Question | Before | Visible working |
|---|---|---|
| Adding shrinkage percent instead of dividing | Multiplying 102 mm by 1.15 gives 117.3 mm, which shrinks to 99.7 mm and misses the target fit. | Use tested total shrinkage for that clay body |
| Using bisque shrinkage for glaze-fired work | High-fire stoneware and porcelain shrink substantially more between bisque and vitrification. | Set your kiln shelf or chamber clearance |
| Checking fired size against kiln shelves | Greenware and bisqueware enter the kiln larger than the final fired piece. | Check the largest wet dimension before throwing |
A local arithmetic aid replaces hand calculation, not expert review. No paid AI service is needed.
Run it on the samples, right here
FIRST-LOAD
Input is processed locally and a draft is saved automatically in this browser profile when storage is available. Reset to sample clears that draft; Pro history has its own clear button. A state link encodes your inputs in its URL: share only non-sensitive rows. Browser history, clipboard and anyone receiving the link may retain it. Optional AI use below leaves this device; it is not required.
Dimensional shrinkage arithmetic from user-supplied test percentages. Not ceramic engineering or kiln-safety advice; shrinkage varies with water content, throwing compression and firing schedule.
Data note: Everything runs in this browser tab on the kiln firing docket: your vessel piece | target fired size mm | clay body shrinkage percent stays on this device, nothing is uploaded, and the reading is rebuilt only when you press run.
Go deeper: the companion app files the same reading as a clerk's docket sheet
The article demo above runs without limits. The companion app keeps a local history, exports the rows as CSV, prints the kiln firing docket reading, and holds your drafts on this device — one free run, then $ 4 one-time for the layer that keeps filing.
The kiln firing docket reading is complete for free. The optional $4 layer adds print, row CSV and the last five local reading summaries; it does not add hidden answers. Checkout is not configured yet; the article demo remains unlimited.
Open the calculate thrown clay dimensions to hit target fired sizes companionBoundary
Dimensional shrinkage arithmetic from user-supplied test percentages. Not ceramic engineering or kiln-safety advice; shrinkage varies with water content, throwing compression and firing schedule.
What this is built on
- Method: Enter the maximum height or diameter your kiln furniture setup accommodates.
- All sample records are invented examples. The app does not fetch measurements, policies, files or personal records.
- Google’s official pricing page, fetched 2026-09-29, lists free-tier access including AI Studio. Optional formatting only; limits and availability can change. Free-tier content may be used to improve products. Never paste private records there.
Before: Multiplying 102 mm by 1.15 gives 117.3 mm, which shrinks to 99.7 mm and misses the target fit. After: the kiln firing docket shows the working beside each named row so the reader can change the assumption and inspect the consequence.
Optional AI formatting, not calculation
For this kiln firing docket, use the free AI Studio interface only if available to you, with no paid API key. Manual entry completes the same workflow for free. Supply only fictional or non-sensitive notes. Review its output against the source; never paste unresolved questions into the numeric rows.
Format my non-sensitive notes for a kiln firing docket. Return plain rows only: vessel piece | target fired size mm | clay body shrinkage percent. Preserve supplied quantities exactly. Do not guess missing values; list questions separately. Do not calculate or add advice. I will check every row before pasting into the local tool.
Accepted schema: vessel piece | target fired size mm | clay body shrinkage percent. No AI response is executed as code.