PFT Calculator
Interpret pulmonary function test results instantly. Calculate FEV1, FVC, FEV1/FVC ratio, and determine lung function severity from spirometry data.
Forced Expiratory Volume in 1 second.
Forced Vital Capacity.
PFT Calculator: Complete Pulmonary Function Test Interpretation
Our PFT calculator is a free online medical tool that helps you interpret pulmonary function test results. Enter your spirometry values — FEV1 and FVC — along with your age, height, and gender to instantly determine predicted values, percentage predictions, and lung function classification. This tool is essential for patients, medical students, and healthcare professionals reviewing respiratory test results.
Pulmonary function tests measure how well your lungs inhale, exhale, and exchange gases. The most common PFT is spirometry, which measures the volume and flow of air during breathing. Our calculator uses standard reference equations to provide accurate interpretation of your results.
How to Use the PFT Calculator
- Enter Your Demographics — Input your age, height in centimeters, and gender (male or female).
- Enter FEV1 Value — Input your Forced Expiratory Volume in 1 second from your spirometry report.
- Enter FVC Value — Input your Forced Vital Capacity from your spirometry report.
- Click Interpret — Get your FEV1 % predicted, FVC % predicted, FEV1/FVC ratio, and severity classification instantly.
PFT Result Interpretation
The FEV1/FVC ratio is the key indicator for obstructive vs restrictive patterns. A ratio below 0.70 or below the lower limit of normal (LLN) suggests obstruction. The FEV1 percentage predicted determines severity of obstruction: mild (70-79%), moderate (60-69%), severe (50-59%), and very severe (below 50%).
PFT Severity Classification Table
| Classification | FEV1 % Predicted | FEV1/FVC Ratio | Common Conditions |
|---|---|---|---|
| Normal | 80% or above | 0.70 or above | Healthy lung function |
| Mild Obstruction | 70-79% | Below 0.70 | Early COPD, mild asthma |
| Moderate Obstruction | 60-69% | Below 0.70 | Moderate COPD, asthma |
| Severe Obstruction | 50-59% | Below 0.70 | Severe COPD |
| Very Severe | Below 50% | Below 0.70 | End-stage COPD, pulmonary fibrosis |
What Is FEV1?
FEV1 (Forced Expiratory Volume in 1 second) is the maximum amount of air you can forcefully exhale in one second after taking a deep breath. It is the most clinically important spirometry measurement. Reduced FEV1 indicates airflow obstruction, which is characteristic of conditions like COPD, asthma, and bronchiectasis. FEV1 is compared to predicted values based on your age, height, gender, and ethnicity.
What Is FVC?
FVC (Forced Vital Capacity) is the total volume of air you can forcefully exhale after inhaling as deeply as possible. It measures total lung capacity. A reduced FVC may indicate restrictive lung disease (pulmonary fibrosis, chest wall deformity) or severe obstruction that traps air. Normal FVC is generally above 80% of the predicted value for your demographics.
Obstructive vs Restrictive Patterns
Understanding the pattern of your PFT results is crucial for diagnosis:
- Obstructive Pattern: Reduced FEV1/FVC ratio (below 0.70) with normal or increased FVC. Seen in COPD, asthma, bronchiectasis, and cystic fibrosis.
- Restrictive Pattern: Normal or elevated FEV1/FVC ratio with reduced FVC. Seen in pulmonary fibrosis, sarcoidosis, chest wall disease, and obesity.
- Mixed Pattern: Both reduced ratio and reduced FVC. Seen in combined diseases like COPD with pulmonary fibrosis.
When Should You Get a PFT?
Your doctor may order PFTs if you experience shortness of breath, chronic cough, wheezing, or chest tightness. PFTs are also used to monitor chronic lung conditions, assess surgery risk, evaluate disability, and track response to treatment. The test is safe, non-invasive, and takes about 15-30 minutes to complete.