How this calculator works
FEV1 is the volume exhaled in the first second of a forced manoeuvre and FVC is the total volume exhaled. Dividing FEV1 by FVC gives the proportion of the vital capacity delivered in that first second. The GOLD strategy uses a post-bronchodilator ratio below 0.70 to confirm persistent airflow limitation. That fixed cut-off is simple but becomes less specific with age, so the ATS/ERS interpretation strategy compares the same ratio with a lower limit of normal derived from reference equations. This page performs the arithmetic and the 0.70 comparison only; it does not choose a diagnosis or a severity grade. The result is an estimate for information only and is not medical advice.
Formula
FEV1/FVC ratio = FEV1 / FVC. Express the result as a fraction or a percentage. The GOLD fixed threshold is a ratio below 0.70 after bronchodilator.
Worked example
FEV1 of 2.0 L with FVC of 4.0 L gives a ratio of 0.50, or 50%, which is below 0.70. FEV1 of 3.6 L with FVC of 4.5 L gives 0.80, or 80%, which is at or above 0.70.
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Frequently asked questions
Should the values be before or after a bronchodilator?
The GOLD threshold uses post-bronchodilator values. Pre-bronchodilator values can reflect reversible narrowing and should be labelled as such.
Why is FEV1 not allowed to exceed FVC?
In one technically acceptable manoeuvre FEV1 is a subset of FVC. A larger FEV1 indicates a transcription or manoeuvre error, so the page rejects it.
Does a ratio below 0.70 prove COPD?
No. It describes an obstruction pattern. Diagnosis needs symptoms, exposure history and clinical assessment, and other conditions can lower the ratio.
Is the fixed 0.70 threshold the only definition?
No. The ATS/ERS strategy uses the lower limit of normal from reference equations, which avoids the age-related over-diagnosis of the fixed ratio.