FEV1/FVC Ratio Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Anna Szczepanek, PhD and Rijk de Wet
Last updated: Feb 18, 2022

The FEV1/FVC ratio calculator serves as the ultimate tool for calculating the Tiffeneau index. No matter if you want to calculate the actual FEV1/FVC ratio of your patient, or you just want to predict the correct values characteristic of their age, ethnicity and height — you've come to the right place. ✅

Enjoy scrolling to the very bottom — we'll show you how to calculate FEV1/FVC percentage and explain the FEV1/FVC ratio meaning in pulmonary medicine.

If you have any questions regarding our calculator, take a look at two explanatory sections: How to use the tool and FVC & FEV1 predicted — how did we do it?

FEV1/FVC ratio explained

We can use FEV1 and FVC to describe different properties of spirometry, the most available and useful pulmonary function test.

Spirometry may be performed when the doctor suspects any kind of airflow obstruction, e.g., asthma or chronic obstructive pulmonary disease (COPD). The test itself is quite simple: a technician will ask you to take the deepest breath possible and then exhale it as fast as you can at the exact moment when they tell you to.

The machine will then measure the amount of air you exhaled during the first second of breathing out and the total amount of air that will leave your mouth. Because you need to take the full breath in at the beginning of the test and then force yourself to exhale it as fast as you can, all the values obtained are called forced:

High values of FEV1 and the FEV1/FVC ratio tell us about the lack of obstruction in the airflow — it means that you're able to "blow out" a large amount of air in a tiny amount of time. A low FEV1/FVC index lets us think not only of the obstruction, but also of restrictions caused by the disease of the pulmonary tissue that suppresses the lungs from achieving their full capacity.

💡 The FEV1/FVC ratio is also called the Tiffeneau index.

What are FEV1/FVC normal values?

  • The normal FEV1/FVC index value exceeds 70% — all the results that are beneath this threshold might be a sign of airflow obstruction and require deeper investigation. This situation changes a bit in people over 65 years old: for this group of patients, the healthy results start at FEV1/FVC 65%.

  • The correct FEV1 value should be greater than 80% of the predicted value.

  • The normal FVC value should be greater than 80% of the predicted value.

Happy with the FEV1/FVC ratio calculator? Don't hesitate to check our other pulmonary tools: 💨

How to use the FEV1/FVC ratio calculator?

Just as easy as it seems! Please use the short summary below in case of any doubts:

  1. Choose between calculating actual, real-life ratio or the predicted values.
  2. If you choose the actual ratio, enter the values of FVC and FEV1.
  3. If you choose prediction:
    • Decide the study you want to base your calculation on. We have two populations to choose from:
      • American, from 1997; and
      • European, from 2004.
    • Depending on the population, enter all the required characteristics of a patient.
  4. Yay! That's it — take a look at your results. 🎉

How to calculate FEV1/FVC ratio?

It's definitely easier than expected — after all, the calculation includes only two variables!

The equation used in our FEV1/FVC ratio calculator looks as follows:

Tiffeneau index = (FEV1 / FVC) * 100%


  • FEV1 is the forced expiratory volume in 1 second, given in liters [L].
  • FVC is the forced vital capacity, given in liters [L].

What are the values of FEV1/FVC in COPD?

FEV1/FVC ratio and index values below 70% are typical for chronic obstructive pulmonary disease (COPD).

We can distinguish a few stages of COPD, designated by the Tiffeneau index and FEV1 values:

  • I — Mild, with FEV1/FVC < 70% and FEV1 > 80% predicted.
  • II — Moderate, with FEV1/FVC < 70% and 50% < FEV1 < 80% predicted.
  • III — Severe, with FEV1/FVC < 70% and 30% < FEV1 < 50% predicted; and
  • IV — Very severe, with FEV1/FVC < 70% and FEV1 < 30% predicted.

How do we calculate lung function test predicted values?

FEV1 and FVC predicted values can be calculated using special equations, determined during extensive research. We decided to use two different methods:

  • As per the American Journal of Respiratory and Critical Care Medicine, the FEV1/FVC index equation is based on the patient's sex, age and ethnicity.

  • The equation found in the European Respiratory Journal is based on sex, age and height.

We used the formulas that correspond with a complete Tiffeneau index, instead of operating two different equations that give us percents predicted on FVC and FEV1 separately. However, bear in mind that such an option is possible, and we'll probably create a calculator on that subject too. 🤓

❗ Our calculators cannot serve as a replacement of actual medical advise and real clinical decisions. Contact medical professional in case of any doubt.


How can you calculate predicted FEV1/FVC values?

There are many different equations for calculating predicted values of lung functions. They're usually based on a given population of the area where the research was conducted.

The most popular formulas call for age, sex, ethnicity and height of a patient. The equations themselves may be both: extremely complicated, and easy enough to be calculated by hand. 👌

Łucja Zaborowska, MD, PhD candidate
Please choose between calculating real ratio or its prediction.
Calculation type
Real ratio
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