pottery calculator
A professional, all-in-one toolkit for ceramic artists and studio managers. Compute clay shrinkage & required green size, plaster–water ratios for molds, glaze batch scaling by recipe percentages & target weight, and unit price per piece including clay, glaze, kiln, and labor. Built for accuracy, mobile usability, and auditability.
Calculator
Required green size
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Green = Final / (1 − s)
Linear shrinkage multiplier
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Multiplier = 1 / (1 − s)
Measured shrinkage (if given)
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s = (G − F) / G
Water needed
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kg (≈ liters)
Plaster needed
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kg
Total slurry
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kg (approx. volume ≈ liters)
| Ingredient | Percent | Weight (g) |
|---|---|---|
| Total dry | — | |
| Est. water (g) | — | |
| Est. slurry (g) | — | |
Material cost / piece
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Labor cost / piece
—
Total cost (with overhead)
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Suggested price
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Data Sources & Methodology
- Shrinkage fundamentals: Linear shrinkage computed as \( s = \frac{G-F}{G} \) (green–to–fired). Guidance on maturation & trends: Digitalfire, “Firing Shrinkage.” Source.
- Green size from final: \( \text{Green} = \frac{\text{Final}}{1-s} \). Practical guidance corroborated by studio literature. Source.
- Plaster-water ratios: Typical ranges around 70–73 parts plaster per 100 parts water by weight (USG No.1 context). References: Glazy Plaster Calculator; PhotoPottery ratio explainer. Source 1, Source 2.
- Glaze batching: Percent scaling of dry recipe to target weight; initial water guideline ~45–60% of slurry by mass depending on clay content and target specific gravity. Practice notes: Glazy Help; studio guides. Source.
- Water absorption context & measurement standards: ASTM C373 methods inform terminology for ceramic bodies. Source.
All calculations strictly follow the formulas and data points provided by the sources above.
The Formulas (Explained)
Shrinkage (empirical): \( s = \dfrac{G - F}{G} \quad (0 \le s < 1) \)
Required green size from target final: \( \text{Green} = \dfrac{\text{Final}}{1 - s} \)
Linear multiplier: \( M = \dfrac{1}{1 - s} \)
Plaster–water (by weight): Given \(P:W\), for water mass \(m_W\) the plaster mass is \( m_P = m_W \cdot \dfrac{P}{W} \). For target volume (L) we approximate \( m_W \approx \text{L} \) (1 L ≈ 1 kg water).
Glaze scaling: For ingredient i with percent \(p_i\), the scaled weight is \( w_i = p_i/100 \cdot W_{\text{dry}} \). Estimated water \( W_{\text{H2O}} \approx \alpha \cdot (W_{\text{dry}} + W_{\text{H2O}}) \Rightarrow W_{\text{H2O}} = \dfrac{\alpha}{1-\alpha} \, W_{\text{dry}} \).
Unit price per piece: Material + Labor + Kiln share → Cost. Overhead markup \( \beta \) on cost: \( C' = C \cdot (1+\beta) \). Target margin \( m \) on price: \( \text{Price} = \dfrac{C'}{1-m} \).
Glossary of Inputs & Outputs
| Field | Meaning |
|---|---|
| Target fired length | Your desired post-firing dimension along any axis. |
| Shrinkage % (s) | Total linear firing shrinkage of the clay body from green to fired. |
| Green size | Size to throw/handbuild to obtain the target final size after shrinkage. |
| Plaster:Water | Weight ratio for mixing pottery plaster slurries. |
| Mold volume (L) | Approximate liters of slurry needed for the mold cavity. |
| Glaze recipe % | Ingredient list as percentages that sum to ~100%. |
| Target dry weight | Total grams of dry materials to mix for the glaze batch. |
| Water % of slurry | Guideline fraction for initial hydration before dialing in SG. |
| Unit price | Suggested selling price meeting your margin after overhead. |
How It Works: A Step-by-Step Example
Example A — Green size from final
Target bowl diameter = 20 cm, shrinkage \( s = 0.12 \) (12%). Using \( \text{Green} = \frac{20}{1-0.12} = 22.73 \) cm. Throw to ~22.7 cm.
Example B — Plaster mix
Mold volume = 3.0 L. Ratio = 70:100 (plaster:water). Approx water \( \approx 3.0 \) kg. Plaster \( = 3.0 \times 70/100 = 2.1 \) kg. Total slurry ≈ 5.1 kg (~5.1 L).
Example C — Glaze scaling
Recipe totals 100%. Target dry = 1,000 g. Each ingredient weight \( = \% \times 10 \). If water fraction \( \alpha = 0.5 \), estimated water \( = \frac{0.5}{0.5}\times1000 = 1000 \) g → slurry ≈ 2000 g.
Example D — Unit price
Clay 600 g @ €2.50/kg → €1.50; Glaze 15 g @ €6/kg → €0.09; Kiln €18 / 24 pcs → €0.75; Labor 25 min @ €20/h → €8.33. Base cost = €10.67. Overhead 15% → €12.27. Margin 40% → Price \( = 12.27/(1-0.4) = €20.45 \).
FAQ
Is shrinkage the same for all directions?
It’s approximately linear but can vary by forming method, wall thickness, and orientation. Test your body with bars or tiles and measure along the same axis you care about.
What shrinkage should I enter—wet to fired or dry to fired?
Use your total green-to-fired linear shrinkage for accurate green size targeting. If you only have dry-to-fired, expect slightly less total shrinkage than wet-to-fired.
How accurate is the plaster volume ≈ mass assumption?
We assume 1 L water ≈ 1 kg for quick planning. Actual slurry density differs; weigh materials for production.
What water percentage should I use for glazes?
Start around 45–60% of total slurry mass, then adjust to reach your target specific gravity and application behavior.
How do I include multiple firings or decals in pricing?
Add their costs to the kiln field (or duplicate the field as needed) and update pieces per firing accordingly.
Can I switch units?
Yes. Keep units consistent within each tool (e.g., all cm or all inches). Currency follows your locale.
Tool developed by Ugo Candido. Content verified by CalcDomain Editorial Board.
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