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Lung Function Test calculator for FEV1, FVC, FEV1/FVC ratio, predicted values, and bronchodilator response. Calculate spirometry results easily.
| Formula | Purpose | Notes |
|---|---|---|
| FEV₁/FVC (%) = (FEV₁÷FVC)×100 | Main obstruction screening ratio | ATS main reported value; use LLN/z-score, not a fixed 70% cutoff |
| FEV₁ % Predicted = (Measured÷Predicted)×100 | Compares to age/sex/height reference | Depends on reference equation used |
| FVC % Predicted = (Measured÷Predicted)×100 | Compares to age/sex/height reference | Depends on reference equation used |
| % Change = [(Post−Pre)÷Pre]×100 | Bronchodilator responsiveness | Classic criterion: ≥12% AND ≥200 mL (guideline-dependent) |
A Lung Function Test calculator helps you understand key spirometry results in a simple way. Our calculator is designed to make common lung function calculations fast and easy. It works with FEV1, FVC, FEV1/FVC ratio, predicted values, and bronchodilator changes.
Spirometry is a common lung function test. It measures how much air you can breathe out and how fast you can do it. The main results are forced vital capacity (FVC) and forced expiratory volume in one second (FEV1).
If you're asking, “How do you calculate FVC and FEV1?” the answer is important: spirometry measures these values directly. A calculator can then compare measured values with predicted values or calculate the FEV1/FVC ratio.
A lung function test checks how well your lungs move air. Spirometry is one of the most common tests.
FEV1 is the amount of air you force out in the first second of a forced breath. FVC is the total amount of air you force out after taking a full breath.
The FEV1/FVC ratio shows how much of your forced vital capacity is exhaled during the first second.
A lower ratio can suggest airflow obstruction, but proper interpretation should use age, sex, height, reference equations, and the lower limit of normal. A fixed 70% cutoff is not suitable for every person.
The main formula used by this Lung Function Test calculator is:
FEV1/FVC (%) = (FEV1 ÷ FVC) × 100
For predicted FEV1:
FEV1 % Predicted = (Measured FEV1 ÷ Predicted FEV1) × 100
For predicted FVC:
FVC % Predicted = (Measured FVC ÷ Predicted FVC) × 100
For bronchodilator response:
Absolute Change = Post-Bronchodilator − Pre-Bronchodilator
Absolute Change (mL) = Absolute Change (L) × 1000
% Change = [(Post − Pre) ÷ Pre] × 100
Your calculator also checks a traditional “classic” response rule of at least 12% improvement and at least 0.200 L (200 mL) increase. This is a calculator rule, not a complete modern clinical interpretation.
Suppose your FEV1 is 3.0 L and your FVC is 4.0 L.
FEV1/FVC (%) = (3.0 ÷ 4.0) × 100
FEV1/FVC = 75%
For a predicted FEV1 example, suppose measured FEV1 is 3.0 L and predicted FEV1 is 3.5 L.
FEV1 % Predicted = (3.0 ÷ 3.5) × 100
FEV1 % Predicted = 85.71%
For a bronchodilator example, suppose pre-test FEV1 is 2.50 L and post-test FEV1 is 2.80 L.
Absolute Change = 2.80 − 2.50 = 0.30 L
0.30 × 1000 = 300 mL
% Change = (0.30 ÷ 2.50) × 100 = 12%
There is no single “good” lung capacity that applies to every age. Expected spirometry values vary with factors such as age, height, sex, and the reference population used.
Modern spirometry interpretation can use Global Lung Function Initiative (GLI) reference equations. This is why a simple FEV1 predicted values calculator should not be treated as a diagnosis.
A spirometry calculator can calculate percentages, but a healthcare professional should interpret the complete lung function test.
The Lung Function Test calculator makes common spirometry math easier. It can calculate the FEV1/FVC ratio, FEV1 percent predicted, FVC percent predicted, and bronchodilator changes in seconds.
If you want to know whether your lung function is normal, don't rely on one number alone. Your age, height, sex, reference values, symptoms, and complete pulmonary function test results all matter.
FEV1 and FVC are normally measured directly by spirometry. The calculator does not measure lung volume. It uses measured results to calculate ratios and percent-predicted values.
There is no single normal FEV1 number for every age. Expected values depend on age, height, sex, and the reference equation used.
A home spirometer may measure some airflow values, but professional spirometry is more appropriate for clinical assessment. A simple peak-flow meter measures a different value and does not replace full spirometry.
It is the percentage obtained by dividing FEV1 by FVC and multiplying by 100. It is an important measure of airflow during spirometry.
No. This calculator does not calculate total lung capacity (TLC). Its predicted-value mode calculates FEV1 and FVC percentages when measured and predicted values are provided.
No. The calculator does not generate GLI predicted values. You must enter the predicted FEV1 or FVC value separately.
No. Your calculator uses 70% as a traditional screening threshold, but modern clinical interpretation should consider the appropriate lower limit of normal and reference equations.