Enter the NCO/OH ratio, the NCO equivalents (eq), and the OH equivalents (eq) into the calculator to determine the missing variable.

NCO/OH Ratio Calculator

Basic ratio from equivalents
Ratio from formulation

Enter exactly 2 values to calculate the missing variable. Use functional-group equivalents (eq), not grams.

Safety notice (isocyanates): For industrial/professional use. Isocyanates can cause respiratory sensitization and serious irritation. Before handling or mixing, read and follow the product Safety Data Sheet (SDS) and supplier technical guidance, use appropriate PPE (e.g., suitable gloves/eye protection and respiratory protection where required), and ensure adequate ventilation/engineering controls. If you’re unsure about exposure controls or safe handling, consult your supplier or a qualified industrial hygiene professional.

Related Calculators

NCO/OH Ratio Formula

The following formula is used to calculate the NCO/OH ratio for a given amount of NCO and OH equivalents.

R = E_{NCO} / E_{OH}

Variables:

  • R is the NCO/OH ratio
  • ENCO is the NCO equivalents (eq)
  • EOH is the OH equivalents (eq)

To calculate the NCO/OH ratio, divide the NCO equivalents by the OH equivalents.

What is an NCO/OH Ratio?

The NCO/OH ratio is a measure used in polymer chemistry to describe the ratio of isocyanate groups (NCO) to hydroxyl groups (OH) in a chemical reaction. This ratio is crucial in determining the properties of the resulting polymer, such as its flexibility, hardness, and durability. By adjusting the NCO/OH ratio, chemists can tailor the characteristics of the polymer to suit specific applications, such as coatings, adhesives, foams, and elastomers.

How to Calculate NCO/OH Ratio?

The following steps outline how to calculate the NCO/OH ratio.

  1. First, determine the NCO equivalents (ENCO).
  2. Next, determine the OH equivalents (EOH).
  3. Finally, calculate the NCO/OH ratio using the formula R = ENCO / EOH.
  4. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

NCO equivalents (ENCO) = 10

OH equivalents (EOH) = 5