Calculator Input
Use the responsive grid below. Large screens show three columns, medium screens show two, and mobile shows one.
Example Data Table
| Case | Sex | Age | Height | Measured FVC | Adjustment | Predicted FVC | % Predicted |
|---|---|---|---|---|---|---|---|
| Example A | Male | 35 | 178 cm | 4.35 L | 1.00 | 4.89 L | 89.0% |
| Example B | Female | 42 | 162 cm | 3.05 L | 0.94 | 3.00 L | 101.5% |
| Example C | Male | 58 | 170 cm | 3.10 L | 0.90 | 3.57 L | 86.9% |
Formula Used
Male predicted FVC (L) = (0.052 × height in cm) − (0.022 × age in years) − 3.60
Female predicted FVC (L) = (0.041 × height in cm) − (0.018 × age in years) − 2.69
Adjusted predicted FVC = base predicted FVC × reference adjustment factor
Percent predicted = (measured FVC ÷ adjusted predicted FVC) × 100
Screening floor = adjusted predicted FVC × selected screening threshold
Use the adjustment factor only when you need a local reference tweak for internal workflow consistency. True lower-limit interpretation should come from validated laboratory reference equations.
How to Use This Calculator
- Enter the patient label if you want it included in exports.
- Select sex and enter the adult age in years.
- Enter height and choose centimeters or inches.
- Add measured FVC if you want percent predicted and variance.
- Set an optional adjustment factor for local reference alignment.
- Choose the screening threshold percentage for your workflow.
- Press the calculate button to display results above the form.
- Use the chart and export buttons to save the output.
Frequently Asked Questions
1. What is predicted FVC?
Predicted FVC is the expected forced vital capacity for a healthy person with similar basic characteristics. It helps compare a measured result against a reference value.
2. Does this calculator diagnose lung disease?
No. This page provides a screening-style estimate. Diagnosis requires full spirometry quality review, validated reference equations, symptoms, history, and clinician interpretation.
3. Why do age and height affect FVC?
Lung volumes generally rise with larger body size and decline with aging. That is why age and height are core inputs in most spirometry reference systems.
4. What does percent predicted mean?
Percent predicted compares the measured FVC with the predicted FVC. A value near or above the selected screening threshold suggests closer alignment with the chosen reference estimate.
5. Why is there an adjustment factor?
Different labs or reference sets may not match one simple equation exactly. The adjustment factor lets you align the estimate to an internal workflow or published local reference choice.
6. Is the screening floor the same as LLN?
No. The screening floor is only a quick percentage-based cutoff. A true lower limit of normal usually comes from validated reference equations and z-score methods.
7. Can I use this for children?
This implementation is intended for adults only. Pediatric interpretation should use age-specific validated reference equations rather than this simplified adult model.
8. Why might hospital results differ from this page?
Hospitals often use validated reference datasets, strict quality checks, bronchodilator context, and full interpretation rules. Those details can change predicted values and final conclusions.