What this calculator does
FEV1/FVC ratio works out share of lung capacity exhaled in the first second of a forced breath, from spirometry. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaFEV1/FVC (%) = (Forced expiratory volume in 1 second / Forced vital capacity) × 100
The inputs explained
| Field | What to enter |
|---|---|
| FEV1 (L) | A number, measured in L. Starts at 3.5. |
| FVC (L) | A number, measured in L. Starts at 4.5. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with fev1
Every other input is held at the calculator’s starting values while fev1 varies. Select any row to load that scenario into the calculator.
How the answer changes with fev1
| FEV1 (L) | FEV1/FVC ratio | Commonly used threshold | Note |
|---|---|---|---|
| 1.75 | 38.9% | below 70% is a common (fixed-ratio) marker of airway obstruction | Spirometry interpretation should use age, sex, height and ethnicity-adjusted predicted values, not this ratio alone. |
| 2.63 | 58.4% | below 70% is a common (fixed-ratio) marker of airway obstruction | Spirometry interpretation should use age, sex, height and ethnicity-adjusted predicted values, not this ratio alone. |
| 3.5 | 77.8% | below 70% is a common (fixed-ratio) marker of airway obstruction | Spirometry interpretation should use age, sex, height and ethnicity-adjusted predicted values, not this ratio alone. |
| 5.25 | 116.7% | below 70% is a common (fixed-ratio) marker of airway obstruction | Spirometry interpretation should use age, sex, height and ethnicity-adjusted predicted values, not this ratio alone. |
| 7 | 155.6% | below 70% is a common (fixed-ratio) marker of airway obstruction | Spirometry interpretation should use age, sex, height and ethnicity-adjusted predicted values, not this ratio alone. |
| 10.5 | 233.3% | below 70% is a common (fixed-ratio) marker of airway obstruction | Spirometry interpretation should use age, sex, height and ethnicity-adjusted predicted values, not this ratio alone. |