FEV1/FVC Ratio Calculator

About this calculator

In spirometry, FEV1 is the volume of air a person can forcefully exhale in the first second of a maximal breath out, and FVC (forced vital capacity) is the total volume exhaled during the entire forced breath. Their ratio, FEV1/FVC expressed as a percentage, describes how much of the total exhaled air comes out quickly — a marker of how freely air flows out of the lungs.

A normal FEV1/FVC ratio is generally around 70–80% or higher in healthy adults (the exact lower limit of normal varies with age, sex and reference equations), and a ratio below that threshold is a hallmark of an obstructive pattern — seen in conditions like COPD and asthma, where narrowed airways slow exhalation even though total lung volume may be near normal. Pulmonologists and respiratory therapists use this ratio, alongside the individual FEV1 and FVC values, as one of the core numbers in interpreting a spirometry test. This calculator computes the FEV1/FVC percentage from the litre values you enter, with a general note on whether it falls in the typical obstructive range — it is not a diagnosis.