Epoxy Stoichiometry Calculator

Calculate the stoichiometric hardener demand for an epoxy resin system from Epoxy Equivalent Weight (EEW) and Amine Hydrogen Equivalent Weight (AHEW). Adjust the stoichiometric index to run epoxy-rich or amine-rich for your application.

Stoichiometric Hardener Demand

phr = (AHEW ÷ EEW) × 100 × (Index ÷ 100)
EEW, AHEW in g/eq  |  phr = parts hardener per 100 parts resin by weight  |  Index 100 = exact 1:1 stoichiometry

Blend EEW/AHEW = Total weight ÷ Σ(weight ÷ component EEW/AHEW)
Same weighted-equivalents rule used for resin blends and hardener blends

Resin Input

Single Resin
One EEW value
Resin Blend
Multiple resins, weighted
From resin technical data sheet.

Resin Blend Components

Effective Blend EEW = —

Hardener Input

Enter AHEW
From datasheet
From amine data
MW ÷ active N–H
Hardener Blend
Multiple curatives

Derive AHEW from Amine Molecular Weight

Count of reactive N–H bonds per molecule, not the number of amine groups.

AHEW = —

From hardener technical data sheet, or use the calculator above.

Hardener Blend Components

Effective Blend AHEW = —

100 = exact 1:1. Below 100 = epoxy-rich, above 100 = amine-rich.
Enter your actual batch size, or leave at 100 for phr directly. For a resin blend, enter the blend's total weight.
Enter EEW and AHEW to check the stoichiometric index

Hardener Required

—

Mix Ratio (Resin : Hardener)

Enter values

Total Mixed Weight

—

Practical Note

This gives the theoretical stoichiometric starting point only. Real coating and adhesive formulations are commonly run slightly off 100% index (typically 90–110%) to tune pot life, cure speed, and film properties — check your specific system's technical literature. For resin or hardener blends, the effective equivalent weight is a weighted-equivalents calculation, not a simple average of EEW/AHEW values by mass — enter each component's own EEW/AHEW and weight, and let the calculator do the weighting. Always verify cure with hardness development or DSC before scaling a batch, and re-confirm EEW/AHEW figures from the current lot's certificate of analysis, since they can shift batch to batch.

Data Sources & References

  1. Lee, H., Neville, K. — Handbook of Epoxy Resins, McGraw-Hill, 1967
  2. Ellis, B. (Ed.) — Chemistry and Technology of Epoxy Resins, Springer, 1993
  3. May, C.A. (Ed.) — Epoxy Resins: Chemistry and Technology, 2nd Ed., Marcel Dekker, 1988
  4. Pham, H.Q., Marks, M.J. — Epoxy Resins, Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, 2005

Stoichiometric mix ratio: phr = (AHEW ÷ EEW) × 100 × (Index ÷ 100). AHEW from amine data: AHEW = Amine MW ÷ Active N–H count.

Built by PolymerDNA — more formulation references in the Formulae Masterbook.

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