FEV1/FVC Ratio Calculator — Spirometry Interpretation
Enter measured FEV1 and FVC from a spirometry report, plus age, sex, and height, to calculate the FEV1/FVC ratio, compare to ERS-predicted values, and classify the pattern as normal, obstructive (with GOLD severity), or restrictive.
L
L
Sex
years
cm
Obstructive — GOLD 2 (Moderate)
- 1
Height in metres
175 ÷ 100 = 1.75 - 2
Predicted FEV1 (ERS 1993, male)
4.30 × 1.75 − 0.029 × 50 − 2.49 = 3.58 L - 3
FEV1/FVC ratio
2.1 ÷ 3.5 × 100 = 60
How does this calculator work?
FEV1/FVC = FEV1 ÷ FVC × 100%. A ratio below 70% signals an obstructive pattern; GOLD severity is then determined by FEV1 % predicted (≥80% = GOLD 1, 50–79% = GOLD 2, 30–49% = GOLD 3, <30% = GOLD 4). Predicted values use Quanjer 1993 ERS equations (age, sex, height). Post-bronchodilator values are required for COPD staging.
Formula
How this is calculated
The FEV1/FVC ratio is the cornerstone of spirometry interpretation. FEV1 is the volume of air exhaled forcefully in the first second; FVC is the total volume exhaled with maximal effort. A ratio below 70% (or below the lower limit of normal, LLN) defines an obstructive ventilatory defect — characteristic of COPD, asthma, and bronchiectasis. When the ratio is ≥ 70% but FEV1 and FVC are both reduced below 80% predicted, a restrictive pattern is suggested, though true restriction requires confirmation by full body plethysmography (TLC measurement).
Predicted values are calculated from the Quanjer 1993 ERS reference equations (Eur Respir J 1993;6 Suppl 16:5–40), which use age, sex, and height to derive expected lung volumes in a healthy European adult population. GOLD (Global Initiative for Obstructive Lung Disease) staging for COPD severity classifies obstruction by post-bronchodilator FEV1 % predicted when the ratio is < 70%: GOLD 1 (mild) ≥ 80%, GOLD 2 (moderate) 50–79%, GOLD 3 (severe) 30–49%, GOLD 4 (very severe) < 30%.
Spirometry interpretation requires at least three acceptable manoeuvres meeting ATS/ERS quality criteria (PEF plateau, reproducibility within 150 mL). Values should be post-bronchodilator for COPD staging. Race/ethnicity correction factors exist (GLI-2012 equations offer broader global reference data) — for non-European populations, the 1993 ERS coefficients may over- or under-predict.
Frequently asked questions
A ratio below 70% indicates an obstructive ventilatory pattern: airflow is limited, meaning the airways are narrowed or collapsing during forced expiration. Common causes include COPD (most often from smoking), asthma, bronchiectasis, and tracheal stenosis. GOLD staging then uses FEV1 % predicted to grade severity.
Both are used in clinical practice. The fixed 70% cut-off (GOLD criteria) is simple and widely used for COPD. However, in older adults (>65) a ratio of 65–70% may be physiologically normal, causing over-diagnosis of COPD with the fixed threshold. Spirometry interpretation guidelines (ATS/ERS, GLI-2012) now recommend LLN based on age, sex, height, and ethnicity as a more accurate standard.
Spirometry is necessary but not sufficient. COPD diagnosis requires post-bronchodilator FEV1/FVC < 0.70 plus compatible symptoms and exposure history. Asthma requires demonstration of reversibility (≥12% and ≥200 mL improvement after bronchodilator) or significant variability over time. Full clinical assessment, including history, examination, and sometimes CT imaging, is required.
TG we-Calculate Editorial Team. (2026). FEV1/FVC Ratio Calculator — Spirometry Interpretation [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/fev1-fvc-ratio-calculator
TG we-Calculate Editorial Team. "FEV1/FVC Ratio Calculator — Spirometry Interpretation." TG we-Calculate. 2026. https://we-calculate.com/calculator/fev1-fvc-ratio-calculator.
TG we-Calculate Editorial Team, "FEV1/FVC Ratio Calculator — Spirometry Interpretation," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/fev1-fvc-ratio-calculator
@misc{wecalculate_fev1_fvc_ratio_calculator, title = {FEV1/FVC Ratio Calculator — Spirometry Interpretation}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/fev1-fvc-ratio-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?