Formula Used
Epoxy value method: EEW = 1000 / epoxy value in eq/kg.
Epoxy group method: EEW = 4300 / epoxy group percent.
Oxirane oxygen method: EEW = 1600 / oxirane oxygen percent.
Titration method: EEW = sample mass × 1000 / [(blank mL − sample mL) × normality].
Blend correction: 1 / EEW blend = resin fraction / resin EEW + modifier fraction / modifier EEW.
Solids correction: EEW as supplied = active blend EEW / solids fraction.
Hardener demand: PHR = AHEW × 100 × stoichiometric index / EEW / hardener active fraction.
How to Use This Calculator
Select the method that matches your available resin data. Enter only the values needed for that method. You may leave other method fields unchanged.
Add resin solids if the material is diluted. Add reactive modifier percent and modifier EEW when the resin blend includes another epoxy-functional component.
Enter hardener AHEW and batch mass to estimate phr and hardener mass. Use 100 percent stoichiometric index for a balanced theoretical cure.
Press Calculate to view results above the form. Use CSV or PDF buttons to save the same calculated result.
Epoxy Equivalent Weight Guide
What EEW Means
Epoxy equivalent weight describes the resin mass that contains one epoxy equivalent. It is a key value in coating, adhesive, composite, and encapsulation work. A lower value means more epoxy groups are present in each gram. A higher value means the resin carries fewer reactive groups. This calculator helps convert common lab data into one working value.
Why It Matters
Curing depends on equivalent balance. Epoxy groups must meet active hydrogen groups from the hardener. If the balance is poor, the cured network may stay soft, brittle, sticky, or weak. Correct EEW also helps compare liquid resin, solid resin, modified blends, and diluted systems. The tool can adjust for solids and reactive modifiers. That makes the result closer to a shop or lab mixture.
Main Inputs
Use epoxy value when a supplier gives equivalents per kilogram. Use epoxy group percent when the data sheet reports epoxy content by mass. Use oxirane oxygen percent for titration reports based on oxygen content. Use the titration method when blank volume, sample volume, normality, and mass are known. Direct equivalent mode is useful when a lab already measured total equivalents.
Practical Mixing Notes
After EEW is known, enter hardener AHEW. The calculator estimates phr, which means hardener parts per hundred parts resin. The stoichiometric index lets you target a slight excess or shortage. Keep it at 100 percent for a balanced theoretical mix. Change it only when your formulation, test plan, or supplier guidance requires it.
Using Results Safely
Treat the answer as a formulation estimate. Real resins may include solvents, fillers, plasticizers, and reactive diluents. Moisture, old material, and incomplete mixing can change cure quality. Always check the technical data sheet. Test small batches before scaling. Record batch mass, temperature, humidity, and cure time. Those records help explain failures and improve repeat work.
Limits and Checks
The number does not replace a specification. It also does not prove cure speed, glass transition, or chemical resistance. Use it with viscosity, functionality, and supplier limits. Round only after the final step. Small rounding errors can affect hardener demand. Save the exported file with each batch record. This gives traceable work for audits, troubleshooting, and repeat production checks later.
FAQs
What is epoxy equivalent weight?
It is the resin mass that contains one equivalent of epoxy groups. The unit is usually grams per equivalent. It helps set the correct hardener amount.
Is lower EEW always better?
No. Lower EEW means more epoxy groups per gram. It may improve crosslink density, but viscosity, flexibility, heat resistance, and process needs also matter.
What is epoxy value?
Epoxy value is epoxy equivalents per kilogram of resin. Convert it to EEW by dividing 1000 by the epoxy value.
What is AHEW?
AHEW means amine hydrogen equivalent weight. It is the hardener mass that supplies one active hydrogen equivalent for reaction with epoxy groups.
Why does solids percent change EEW?
Solvent or nonreactive material adds mass without adding epoxy groups. That raises the as supplied EEW and changes the hardener demand.
Can I use this for reactive diluents?
Yes. Enter the reactive modifier percent and its EEW. The calculator combines equivalent contributions by weight fraction.
What stoichiometric index should I use?
Use 100 percent for a balanced theoretical mix. Change it only when a supplier, test plan, or known formulation requires a different ratio.
Does this replace lab testing?
No. It gives a formulation estimate. Cure, adhesion, strength, and resistance should still be checked with controlled practical testing.