A conversion factor turns product weight into steviol. The calculation is the steviol molecular weight, 318, divided by the component molecular weight: stevioside 0.40, Reb A 0.33, Reb D 0.28, Reb M 0.25. On the same 1 kg steviol-equivalent allowance you can use 4.0 kg of Reb M product but only 2.5 kg of stevioside.
GB 2760 sets the maximum use level for steviol glycosides in steviol equivalents, not in product weight, and the ADI of 0-4 mg/kg bw uses the same basis. Steviol glycosides are a mixture of thirteen glycosides with molecular weights from 805 to 1291, so a gram of one product does not carry the same amount of steviol as a gram of another. Only by converting back to the aglycone can products with different compositions be compared.
| Component | Molecular weight | Conversion factor | Steviol equivalent per 1 kg product |
|---|
| Stevioside (STv) | 805 | 0.40 | 0.40 kg |
| Reb A | 967 | 0.33 | 0.33 kg |
| Reb D | 1129 | 0.28 | 0.28 kg |
| Reb M | 1291 | 0.25 | 0.25 kg |
Table 1 - Conversion factors for the four main components.
A commercial product is not a pure single component, so the real calculation needs two inputs: the total glycoside content and the share of each component. The method is to multiply each component content by its own factor and add the results - not to multiply the total glycoside figure by a single factor.
Worked example: beverages
Take food category 14.0 in GB 2760-2024, beverages: the limit is 0.2 g/kg expressed as steviol equivalents and measured as consumed. Applying the factors to three grades shows what that limit means in product:
| Grade | Conversion (component × factor) | Product allowed per kg of beverage |
|---|
| RA97 | 0.97 × 0.33 ≈ 0.32 | ≈ 0.62 g |
| ST95-RA60 | 0.60 × 0.33 + 0.35 × 0.40 ≈ 0.34 | ≈ 0.59 g |
| Reb M 95% | 0.95 × 0.25 ≈ 0.24 | ≈ 0.84 g |
Table 2 - Three high-purity grades under the same 0.2 g/kg limit. Contents are as declared on the label and are illustrative; use the COA component table in practice. In ST95-RA60 the undeclared 35% is treated as stevioside; if another glycoside dominates, the factor shifts slightly.
Three products all around “95%” therefore allow anything from 0.59 g to 0.84 g per kg - a spread of about 40%. That is not a difference in testing convention; it is molecular weight.
Three common mistakes
- Comparing product weight directly with the limit. Every factor is below 1, so product weight is always larger than the steviol equivalent - comparing the two directly guarantees an overdose.
- Using 0.33 for everything. In the ST series the stevioside factor is 0.40; using 0.33 underestimates the equivalent and is the riskiest of the three errors.
- Treating “95% total glycosides” as a factor. Total glycosides is a sum of contents, not a conversion factor. The two cannot be mixed.
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Do the arithmetic on the component table of the COA, not on the headline purity figure.
Primary sources: GB 2760-2024 (beverages 0.2 g/kg, expressed as steviol equivalents); JECFA Table A (original conversion factors)
Related products: Optimvia Reb-M / Reb-D · Reb-A Series