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Total Rare Earth Oxide (TREO) Calculator

Convert a multi-element rare-earth assay (La–Lu plus Y) into rare-earth oxide equivalents, total TREO and LREO/HREO subgroups — with the oxide form used per element and the grouping definition shown.

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How to use this calculator

REE assay

Grouping conventions vary. The oxide form per element and the group definition are shown with the result.

Rare earth oxides

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

More needed
  • Enter at least one REE concentration.
Assumptions & basis
  • Oxide forms: Ce=CeO₂, Pr=Pr₆O₁₁, Tb=Tb₄O₇, others REE₂O₃ (oxides-1.0 / IUPAC-2021-conventional) (derived)
  • Grouping: LREE (La–Eu) / HREE (Gd–Lu + Y) (user)

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. Enter each REE concentration in the same unit (ppm, wt% or g/t).
  2. Read each element's oxide equivalent (REO), the TREO total and the LREO/HREO subgroups.
  3. The oxide form (e.g. CeO₂, Pr₆O₁₁, Tb₄O₇) and the group definition are shown with the results.

How it works

Each element is converted to its conventional commercial oxide by a stoichiometric factor derived from the versioned atomic-weight table: REO_i = element_i × (oxide molar mass ÷ (n · element weight)). TREO is the sum of the included oxide equivalents. Cerium is reported as CeO₂, praseodymium as Pr₆O₁₁ and terbium as Tb₄O₇; the other REE use the sesquioxide RE₂O₃.

Rare-earth grouping conventions are not universal, so the tool states which definition it uses (here LREE = La–Eu, HREE = Gd–Lu plus Y) and which elements are included in each total, rather than presenting one grouping as the only correct one.

Worked example

Converting La, Ce and Nd. 1,000 ppm La becomes 1,172.8 ppm La₂O₃ (×1.17276); 2,000 ppm Ce becomes 2,456.7 ppm CeO₂ (×1.22836); 800 ppm Nd becomes 933.1 ppm Nd₂O₃ (×1.16638). TREO is the sum of every element's oxide equivalent.

Common mistakes

  • Mixing units between elements — keep them all in ppm (or all wt%).
  • Assuming one LREE/HREE split is standard; definitions differ between publications.
  • Forgetting that Ce, Pr and Tb use non-sesquioxide forms, which changes their factors.

Frequently asked questions

Which oxide form is used for each element?

Ce → CeO₂, Pr → Pr₆O₁₁, Tb → Tb₄O₇, and the remaining REE → RE₂O₃. These conventional commercial forms are shown next to the result, with factors derived from the atomic-weight table.

Is the LREE/HREE split fixed?

No. This tool uses La–Eu (light) and Gd–Lu + Y (heavy) and states so, but other publications draw the line differently. The included elements are always listed.

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Cite this tool

Zerdly. (2026). Total Rare Earth Oxide (TREO) Calculator. Retrieved from https://www.zerdly.com/tools/treo-calculator/

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

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