Loss on Ignition (LOI) Calculator
Glaze
claycalc.com
Loss on Ignition (LOI) Calculator
Calculate the fired weight of a glaze or clay batch after materials lose mass during firing, and scale batch weights to hit a target fired quantity.
Reviewed by ClayCalc Editorial · Updated
Enter up to 10 materials with batch weight and LOI%. Common LOI values: Whiting 44%, Dolomite 48%, Gerstley Borate 27%, EPK Kaolin 13%, Talc 5.5%, Silica 0%.
Results
Enter your measurements above and click Calculate.
What is Loss on Ignition (LOI)?
LOI is the percentage of a raw ceramic material's weight that is lost as gas during firing. Carbonates release CO₂, while clays and hydrated minerals release water (H₂O) from their crystal structure. The fired material weighs less than the raw material.
Why It Matters
When calculating glaze chemistry (UMF / Seger formula), you work with the fired oxide amounts — not the raw batch weights. High-LOI materials like whiting contribute fewer oxides per gram of batch weight than their formula weight suggests, because much of the batch weight disappears as gas.
Formula
Fired weight (g) = Batch weight × (1 − LOI% / 100) Weight loss (g) = Batch weight − Fired weight Overall LOI% = Total weight loss / Total batch weight × 100
Common Material LOI Reference
| Material | LOI % | Gas Released |
|---|---|---|
| Whiting (CaCO₃) | 43.97 | CO₂ |
| Dolomite | 47.57 | CO₂ |
| Gerstley Borate | 26.6 | H₂O + CO₂ |
| EPK Kaolin | 12.8 | H₂O |
| Ball Clay | ~10.5 | H₂O + organic |
| Talc | 5.5 | H₂O |
| Wollastonite | 4.5 | CO₂ |
| Feldspar (G200) | 0.5 | Trace |
| Silica / Quartz | 0.0 | None |
| Zinc Oxide | 0.0 | None |
LOI values vary slightly by source material. Check your supplier's data sheet for precise values.
Method & review note
About this calculation
Performs recipe and slurry arithmetic. A calculated percentage or expansion estimate cannot establish glaze durability, fit, toxicity, or food-contact suitability.
Reference: Digitalfire — Ceramic Glaze. See the editorial methodology for testing, precision and corrections.
Input handling: Values are sent to the ClayCalc server for this request and are not written to the application database.