pottery calculator

Professional pottery calculator: compute clay shrinkage & green size, plaster water ratios, glaze batch scaling by recipe percentages, and per-piece unit pricing with kiln & labor. Mobile-first, accessible, and citation-backed.

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

Enter any linear dimension you care about (e.g., bowl diameter). Units are arbitrary but must be consistent.

Typical stoneware: 10–15%; porcelain often 12–16%. Use your body’s tested value.

If you also know the fired length, we’ll compute actual shrinkage.

Pair with the green length for empirical shrinkage %.

Required green size

—

Green = Final / (1 − s)

Linear shrinkage multiplier

—

Multiplier = 1 / (1 − s)

Measured shrinkage (if given)

—

s = (G − F) / G

Results update live as you type. Units are consistent across each tool (e.g., cm or inches), and currencies are displayed using your locale.

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

FieldMeaning
Target fired lengthYour desired post-firing dimension along any axis.
Shrinkage % (s)Total linear firing shrinkage of the clay body from green to fired.
Green sizeSize to throw/handbuild to obtain the target final size after shrinkage.
Plaster:WaterWeight 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 weightTotal grams of dry materials to mix for the glaze batch.
Water % of slurryGuideline fraction for initial hydration before dialing in SG.
Unit priceSuggested 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.

Last accuracy review:

Audit: Complete
Formula (LaTeX) + variables + units
This section shows the formulas used by the calculator engine, plus variable definitions and units.
Formula (extracted LaTeX)
\[= (sel) => Array.from(document.querySelectorAll(sel)); const clamp = (v, min, max) => Math.min(Math.max(v, min), max); // Accessible tooltips: toggle via button next to label\]
= (sel) => Array.from(document.querySelectorAll(sel)); const clamp = (v, min, max) => Math.min(Math.max(v, min), max); // Accessible tooltips: toggle via button next to label
Formula (extracted LaTeX)
\[(".tab-btn"); const panels = [ "#panel-shrink", "#panel-plaster", "#panel-glaze", "#panel-price" ].map(id => $(id)); function selectTab(index){ tabs.forEach((t,i)=>{ t.setAttribute('aria-selected', String(i===index)); panels[i].hidden = i!==index; }); } tabs.forEach((t,i)=>{ t.addEventListener('click', ()=>selectTab(i)); t.addEventListener('keydown', (ev)=>{ if(ev.key==='ArrowRight') { selectTab((i+1)%tabs.length); tabs[(i+1)%tabs.length].focus(); } if(ev.key==='ArrowLeft') { selectTab((i-1+tabs.length)%tabs.length); tabs[(i-1+tabs.length)%tabs.length].focus(); } }); }); selectTab(0); // ---------- Validations (on blur) ---------- function setErr(id, msg){ const el = $("#"+id); const err = $("#"+id+"_err"); if(!err) return; err.textContent = msg || ""; if(msg){ el.setAttribute('aria-invalid','true'); } else { el.removeAttribute('aria-invalid'); } }\]
(".tab-btn"); const panels = [ "#panel-shrink", "#panel-plaster", "#panel-glaze", "#panel-price" ].map(id => $(id)); function selectTab(index){ tabs.forEach((t,i)=>{ t.setAttribute('aria-selected', String(i===index)); panels[i].hidden = i!==index; }); } tabs.forEach((t,i)=>{ t.addEventListener('click', ()=>selectTab(i)); t.addEventListener('keydown', (ev)=>{ if(ev.key==='ArrowRight') { selectTab((i+1)%tabs.length); tabs[(i+1)%tabs.length].focus(); } if(ev.key==='ArrowLeft') { selectTab((i-1+tabs.length)%tabs.length); tabs[(i-1+tabs.length)%tabs.length].focus(); } }); }); selectTab(0); // ---------- Validations (on blur) ---------- function setErr(id, msg){ const el = $("#"+id); const err = $("#"+id+"_err"); if(!err) return; err.textContent = msg || ""; if(msg){ el.setAttribute('aria-invalid','true'); } else { el.removeAttribute('aria-invalid'); } }
Formula (extracted text)
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: \( \text{Price} = \dfrac{C'}{1-m} \).
Variables and units
  • No variables provided in audit spec.
Sources (authoritative):
Changelog
Version: 0.1.0-draft
Last code update: 2026-01-19
0.1.0-draft · 2026-01-19
  • Initial audit spec draft generated from HTML extraction (review required).
  • Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
  • Confirm sources are authoritative and relevant to the calculator methodology.
Verified by Ugo Candido on 2026-01-19
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Full original guide (expanded)

CalcDomain
Formulas

(Formulas preserved from original page content, if present.)

Version 0.1.0-draft
Citations

Add authoritative sources relevant to this calculator (standards bodies, manuals, official docs).

Changelog
  • 0.1.0-draft — 2026-01-19: Initial draft (review required).