FEV1/FVC Ratio Calculator

The FEV1/FVC ratio — also called the Tiffeneau-Pinelli index — is the cornerstone of pulmonary function testing and the primary criterion used to diagnose obstructive lung disease. FEV1, or forced expiratory volume in one second, is the maximum volume of air that can be exhaled in the first second of a forced expiratory maneuver. FVC, or forced vital capacity, is the total volume exhaled during that same maximal effort. The ratio of these two measurements tells clinicians how easily air flows out of the lungs: in healthy lungs, most of the FVC is expelled in the first second, producing a high ratio; in obstructed lungs, where narrowed airways slow airflow, a smaller fraction exits in the first second, producing a lower ratio. According to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines — the international standard for COPD diagnosis and management — a post-bronchodilator FEV1/FVC ratio below 0.70 (70%) confirms the presence of persistent airflow limitation and is required for a diagnosis of COPD. The severity of COPD is then classified by the degree of FEV1 reduction: GOLD 1 (mild) has FEV1 ≥80% predicted, GOLD 2 (moderate) is 50–79%, GOLD 3 (severe) is 30–49%, and GOLD 4 (very severe) is below 30% predicted. Other obstructive conditions, including asthma, bronchiectasis, and obliterative bronchiolitis, also produce a reduced FEV1/FVC ratio, though asthma is characterised by reversibility after bronchodilator administration. It is important to distinguish obstructive from restrictive ventilatory defects. In restrictive disease (pulmonary fibrosis, pleural disease, neuromuscular weakness, obesity), both FEV1 and FVC fall proportionally, so the ratio remains normal or even elevated despite reduced lung volumes. True diagnosis of restriction requires measurement of total lung capacity (TLC) by body plethysmography. A reduced FVC with a normal FEV1/FVC ratio should prompt investigation for a restrictive cause rather than an obstructive one. The lower limit of normal (LLN) approach, favoured by many respiratory societies, defines obstruction as a ratio below the 5th percentile of the reference population rather than using the fixed 0.70 cutoff. The fixed cutoff slightly over-diagnoses obstruction in the elderly (who have naturally lower ratios) and may under-diagnose it in young adults. Predicted values and reference equations vary by age, sex, height, and ethnicity. This calculator uses the fixed 0.70 threshold as a practical clinical starting point; for full spirometric interpretation, reference to standardised prediction equations is recommended. Proper spirometry technique is essential for valid results. Patients should take a full breath in, seal their lips around the mouthpiece, and then blast air out as forcefully and completely as possible for at least six seconds. At least three acceptable manoeuvres are recorded and the best FEV1 and best FVC from acceptable efforts are selected. Acceptable manoeuvres must meet specific criteria for effort and repeatability defined by the American Thoracic Society / European Respiratory Society (ATS/ERS) spirometry standards. Always interpret spirometry results in clinical context alongside symptoms, history, and imaging.