Zerdly

Loss on Ignition (LOI) Calculator

Calculate loss on ignition (LOI %) from a dry and ignited sample mass, or from crucible tare weighings — the mass change on ignition only, including a mass-gain (negative LOI) case.

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How to use this calculator

Weighings

Calculates mass change only. LOI can include several volatile or oxidation effects — it is not organic content or mineralogy.

Result

Runs entirely in your browser. Your assay data is not uploaded or stored by Zerdly.

More needed
  • Enter the dry and ignited sample masses.
Assumptions & basis
  • Scope: Mass change only — not organic content or mineralogy (derived)

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

  1. Pick a method: enter the dry and ignited sample masses, or the empty crucible plus crucible+dry and crucible+ignited masses.
  2. Read the LOI %, the retained mass % and the mass change.
  3. A negative LOI (mass gain) is shown and flagged, not forced to zero.

How it works

Loss on ignition is the mass a sample loses when heated to a defined temperature, expressed against the dry sample mass: LOI% = (dry − ignited) / dry × 100, and retained% = 100 − LOI%. In the crucible method the tool subtracts the empty-crucible tare from each weighing first, so you enter exactly what the balance reads.

LOI can combine several effects — free and structural water, carbonate CO₂, organic combustion, sulfur loss — and in some materials oxidation causes a mass GAIN, giving a negative LOI. This tool reports the mass change only; it deliberately does not infer organic content or mineralogy, because that depends on the material and the ignition method.

Worked example

A 10.000 g sample igniting to 9.200 g. LOI% = (10.000 − 9.200) / 10.000 × 100 = 8.00%, so 92.00% of the dry mass is retained and 0.800 g was lost on ignition.

Common mistakes

  • Forgetting to subtract the crucible tare in the tare method.
  • Assuming LOI equals organic matter or water — it can be several things at once.
  • Forcing a negative LOI to zero; a genuine mass gain is real information.

Frequently asked questions

Can LOI be negative?

Yes. If the sample oxidises and gains mass on ignition, the ignited mass exceeds the dry mass and LOI is negative. The tool reports it and flags it rather than clamping to zero.

Does LOI tell me the organic content?

Not by itself. LOI is a total mass change and can include water, carbonate CO₂, sulfur and oxidation effects. Interpreting it as organic content requires a method and material assumption this tool does not make.

Related tools

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Cite this tool

Zerdly. (2026). Loss on Ignition (LOI) Calculator. Retrieved from https://www.zerdly.com/tools/loss-on-ignition-calculator/

Tip: Enter any known values to calculate the remaining results.

All calculations run in your browser. Your inputs are never saved or transmitted.