Reaction Mass Efficiency calculator.
Calculate the RME of any chemical reaction from the actual masses of reactants and the isolated product. A single number that captures atom economy, yield, and stoichiometric efficiency together — results update live as you type.
What is Reaction Mass Efficiency — and why does it matter?
Reaction Mass Efficiency (RME) is a practical green chemistry metric that measures what fraction of the total mass of reactants is actually converted into the desired product. Unlike atom economy, which is calculated from the balanced equation alone, RME uses the actual masses weighed out in the lab — so it automatically captures the combined effect of atom economy, reaction yield, and any stoichiometric excess in a single number.
The formula
| Symbol | Term | Units |
|---|---|---|
| $\text{RME}$ | Reaction Mass Efficiency | % (0–100); ideal value = 100% |
| $m_{\text{product}}$ | Mass of desired product actually isolated | g (or kg) |
| $\sum m_{\text{reactants}}$ | Total mass of all reactants used (excluding solvents, catalysts, and workup materials) | g (or kg) |
Solvents, catalysts, and workup reagents are not included in the RME denominator — they are captured by E-factor and PMI. RME is a reactant-only metric. A higher RME is always better.
Typical RME by reaction type
| Reaction type / scenario | Typical RME | Key driver |
|---|---|---|
| Addition / Cycloaddition with high yield | 75–95% | High atom economy and good yield combine favourably |
| Condensation (e.g. esterification, amide bond) | 55–75% | Small molecule lost as by-product lowers atom economy |
| Substitution with stoichiometric leaving-group reagent | 30–60% | Heavy leaving group wasted; excess reagent common |
| Reduction (LiAlH₄ or NaBH₄, stoichiometric) | 20–50% | Heavy reductant contributes to denominator |
| Oxidation with stoichiometric oxidant | <30% | Heavy metal oxidants dominate reactant mass |
| Catalytic hydrogenation (H₂, metal catalyst) | 80–98% | H₂ is light; catalyst not consumed and not counted |
Strengths and limitations
Strengths
- Practical: uses real experimental masses — no need to calculate atom economy or yield separately
- Captures three inefficiencies in one number: poor atom economy, low yield, and excess reagents
- Easy to calculate immediately after an experiment, directly from lab records
- Directly comparable across different synthetic routes to the same target
- Aligns environmental and economic goals — less waste means lower material costs
Limitations
- Does not account for solvents, workup reagents, or water — use E-factor or PMI for that
- Cannot be calculated at the design stage (requires actual masses from the lab)
- Does not distinguish between a low-AE reaction run cleanly and a high-AE reaction with poor yield
- Does not reflect the hazard, toxicity, or energy consumption associated with waste
- Can be misleading if a very heavy (but cheap and benign) reagent is used in large excess
RME in context: complementary green metrics
| Metric | What it measures | Stage |
|---|---|---|
| Atom Economy (AE) | Theoretical fraction of reactant MW in desired product (balanced equation only; no yield or excess) | Design |
| % Yield | Fraction of the theoretical product actually isolated, based on the limiting reagent | Experimental |
| RME (Reaction Mass Efficiency) | Fraction of total reactant mass converted to desired product — captures AE + yield + stoichiometry together | Experimental |
| E-factor | Mass of all waste (including solvents) per mass of product — full process scope | Experimental |
| PMI (Process Mass Intensity) | Total mass of all inputs per mass of product; PMI = E-factor + 1 | Experimental |
Experiment details
Reactants
Enter each reactant with its actual mass used. Do not include catalysts or solvents — catalysts are not consumed, and solvents are not incorporated into the product. Use E-factor or PMI for a full process mass assessment.
| Reactant name | Formula (optional) | Mass used (g) | % of total |
|---|
Products
Enter the actual mass isolated for the desired product. Add any characterised by-products for a complete mass-balance check — only the desired product mass contributes to the RME numerator.
| Compound name | Formula (optional) | Mass (g) | Role | % of reactants |
|---|
Results
Reactant mass contributions
Product vs. mass loss
Detailed breakdown & interpretation
| Compound | Role | Formula | Mass (g) | % of Σ reactants | Visual |
|---|---|---|---|---|---|
| Enter reactants and at least one desired product above to see breakdown. | |||||
Interpretation
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Export
Export your RME calculation as a PDF report or CSV data file. PDF opens in a new tab and uses your browser's print function. CSV downloads directly.
Where can I read more?
References are sorted alphabetically by first author.
- P. T. Anastas and J. C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, 1998. ISBN 978-0-19-850698-0. — Original statement of the 12 Principles; frames atom economy and mass efficiency as central to green synthesis.
- D. J. C. Constable et al., Green Chem., 2007, 9, 411–420. DOI. — Industry perspective on green chemistry metrics in pharmaceutical process development.
- C. Jiménez-González et al., Org. Process Res. Dev., 2011, 15, 912–917. DOI. — Defines PMI and benchmarks solvent use; contextualises RME within the broader toolkit.
- R. A. Sheldon, Pure Appl. Chem., 2000, 72, 1233–1246. DOI. — Introduces RME alongside atom economy and E-factor as complementary metrics.
- R. A. Sheldon, Green Chem., 2017, 19, 18–43. DOI. — E-factor 25 years on; discusses the relationship between RME, AE, yield, and stoichiometric excess.
- B. M. Trost, Science, 1991, 254, 1471–1477. DOI. — The original atom economy paper; foundational for understanding why reactant mass efficiency matters.
Contributors
Roles follow the CRediT taxonomy (Contributor Roles Taxonomy), adapted for educational software. Hover a contributor's name for a summary, or a column header for the definition of that role.
| Contributor |
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