Calculate the FEV1/FVC ratio with percent-predicted context, fixed-ratio obstruction screening, and bronchodilator response framing.
The FEV₁/FVC ratio is one of the main spirometry measures used to sort airflow limitation into obstructive versus restrictive-looking patterns. FEV₁ (forced expiratory volume in 1 second) measures how much air is exhaled in the first second of a forced maneuver, while FVC (forced vital capacity) measures the total forced exhaled volume.
This page uses the fixed-ratio approach commonly discussed in COPD guidance, where a post-bronchodilator FEV₁/FVC below 0.70 supports an obstructive pattern in the right clinical setting. It also shows estimated percent-predicted values and the usual ≥ 12% and ≥ 200 mL bronchodilator-response threshold so the raw ratio is not interpreted in isolation.
The output is meant to support spirometry review, not to replace a full pulmonary-function interpretation. Low FVC with a preserved ratio can suggest restriction, but true restriction needs lung-volume testing, and both technique quality and patient context materially affect how the numbers should be read.
The FEV₁/FVC ratio is the key first step in separating obstructive from restrictive spirometry patterns. This calculator keeps the measured values, predicted values, and bronchodilator response together so the interpretation stays anchored to the same test rather than to a single ratio in isolation.
FEV₁/FVC Ratio = FEV₁ / FVC. COPD confirmed if post-BD ratio < 0.70. Predicted FEV₁ from NHANES III equations based on age, sex, height. BD Reversibility: positive if ΔFEV₁ ≥ 200 mL AND ≥ 12% from baseline.
Result: FEV₁/FVC = 51.4% — Obstructive, GOLD 2 (Moderate)
FEV₁/FVC = 1.8/3.5 = 0.514 (< 0.70, confirming obstruction). FEV₁ is ~55% predicted, placing this in GOLD Stage 2 (moderate COPD).
A low FEV₁/FVC ratio points toward obstruction, but the result is more useful when it is paired with FEV₁ percent predicted and the post-bronchodilator response. If the ratio is preserved and the FVC is low, the pattern shifts toward possible restriction and needs TLC to confirm it.
The post-bronchodilator value is what separates fixed obstruction from reversible airflow limitation. That is why COPD diagnosis depends on the post-treatment ratio, while asthma often shows a measurable improvement after bronchodilator administration.
Predicted values help show how far the measured result sits from expected lung function for that person. They are especially useful when symptoms are present but the raw ratio alone does not capture the full severity of the impairment.
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This page calculates the measured FEV₁/FVC ratio from the entered spirometry values, estimates percent-predicted context from simplified reference equations based on age, sex, and height, and applies the usual fixed-ratio obstruction threshold of 0.70 together with the common bronchodilator-response threshold of ≥ 12% and ≥ 200 mL.
The output is intended as a structured spirometry review aid rather than a complete pulmonary-function interpretation. Proper diagnosis still depends on maneuver quality, whether the values are pre- or post-bronchodilator, the full flow-volume pattern, symptoms, and—when restriction is suspected—formal lung-volume testing.
Under the common fixed-ratio approach, a value below 0.70 supports airflow obstruction. The result still needs to be interpreted with test quality, symptoms, bronchodilator response, and the rest of the pulmonary workup.
COPD typically shows irreversible obstruction (< 200 mL or < 12% improvement post-bronchodilator), while asthma usually shows significant reversibility. However, there is overlap — some COPD patients show partial reversibility.
When both FEV₁ and FVC are reduced but the ratio is preserved (≥ 0.70), restriction is suspected. This must be confirmed by measuring total lung capacity (TLC < 80% predicted) via body plethysmography.
No. The fixed 0.70 cutoff can overdiagnose COPD in elderly patients (where the ratio naturally declines) and underdiagnose in younger patients. The lower limit of normal (LLN) from GLI-2012 is an alternative approach.
Spirometry is indicated for evaluation of dyspnea, chronic cough, wheezing, suspected COPD or asthma, preoperative assessment, monitoring of known lung disease, and occupational exposure screening. The test is most useful when symptoms or risk factors suggest airflow limitation that needs objective measurement.
Proper technique is critical: maximal inspiration followed by blast exhalation for ≥ 6 seconds. Common errors include poor effort, early termination, coughing, and air leaks around the mouthpiece.