Calculate predicted FEV1, FVC, and FEV1/FVC values from reference equations and compare measured results against those predicted values.
The Spirometry Predicted Value Calculator computes expected FEV1, FVC, and FEV1/FVC values from age, sex, height, and ethnicity inputs. The main purpose of the page is to place measured spirometry values next to a reference value so the percent-predicted figures are easier to review.
The predicted values shown here use the NHANES III / Hankinson-style reference framework commonly used in adult spirometry interpretation. When measured values are entered, the page compares them with the reference values and shows broad obstruction/restriction context.
This is a comparison worksheet, not a full pulmonary-function interpretation engine. Formal spirometry interpretation still depends on test quality, bronchodilator status, lower-limit-of-normal context, symptoms, and the broader pulmonary workup.
Predicted values make spirometry easier to read because normal lung volumes vary substantially with age, sex, height, and ethnicity. This page keeps the reference values and percent-predicted calculations together so the measured numbers can be reviewed in context before the formal clinical interpretation is made.
Hankinson/NHANES III Reference Equations (adults): Males (Caucasian): FEV1 = 0.5536 − 0.01303 × Age − 0.000172 × Age² + 0.00014098 × Ht² FVC = −0.1933 + 0.00064 × Age − 0.000269 × Age² + 0.00018642 × Ht² Females (Caucasian): FEV1 = 0.4333 − 0.00361 × Age − 0.000194 × Age² + 0.00011496 × Ht² FVC = −0.3560 + 0.01870 × Age − 0.000382 × Age² + 0.00014815 × Ht² Ht = height in cm; Age in years Ethnicity corrections: • African American: multiply by 0.88 • Asian/Hispanic: multiply by 0.93 GOLD Classification (post-bronchodilator FEV1/FVC < 0.70): • GOLD 1 (Mild): FEV1 ≥ 80% predicted • GOLD 2 (Moderate): 50–80% • GOLD 3 (Severe): 30–50% • GOLD 4 (Very Severe): < 30%
Result: FEV1: 59% predicted (GOLD 2 — Moderate) | FVC: 82% predicted | Ratio: 0.60
The predicted FEV1 for a 55-year-old Caucasian male at 175 cm is approximately 3.55 L. A measured FEV1 of 2.1 L gives 59% of predicted, and with FEV1/FVC of 0.60 (below 0.70), this confirms obstructive disease classified as GOLD Stage 2 (Moderate). FVC at 82% suggests no significant restrictive component.
Percent-predicted values help answer a simple question: how far is the measured number from the expected reference value for someone with similar basic characteristics? That makes them useful for comparison across time and across patients.
A low FEV1/FVC ratio can suggest an obstructive pattern, and a low FVC with a preserved ratio can suggest a restrictive pattern, but formal interpretation still depends on test quality, bronchodilator context, and sometimes fuller lung-volume testing.
Use the calculator to organize predicted values, measured values, and percent-predicted comparisons in one place. It is a reference worksheet, not a stand-alone diagnosis or severity engine.
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This page is a comparison worksheet. It applies the simplified NHANES III / Hankinson-style adult reference equations already implemented in the calculator, then compares optional measured FEV1 and FVC values against those reference numbers to show percent-predicted values and a broad fixed-ratio pattern label. Because the underlying page uses legacy race/ethnicity adjustments and a fixed 0.70 obstruction cutoff, the output should be treated as reference context rather than as a laboratory-grade interpretation or lower-limit-of-normal assessment.
FEV1 is the volume of air you can forcefully exhale in the first one second. FVC is the total volume exhaled during the entire forced breath. In healthy lungs, you can exhale about 75–80% of your total in the first second (FEV1/FVC = 0.75–0.80). In obstructive disease (asthma, COPD), the ratio drops because the narrowed airways slow exhalation. In restrictive disease, both FEV1 and FVC decrease, but the ratio remains normal or elevated.
GOLD staging is a commonly used COPD severity framework based on post-bronchodilator FEV1 percent predicted. On this page it is shown as broad context only; it does not replace the rest of the COPD assessment or decide treatment by itself.
Reference equations often include ethnicity adjustments because published prediction sets differ by population. Those adjustments are only part of the interpretation and do not replace the actual laboratory standard used by the testing center.
The LLN is the 5th percentile of the predicted value distribution for a person's age, sex, height, and ethnicity. Using LLN instead of a fixed FEV1/FVC cutoff of 0.70 avoids over-diagnosing COPD in elderly patients (whose ratio naturally decreases with age) and under-diagnosing it in younger patients. Current ATS/ERS guidelines recommend LLN, while GOLD still uses the fixed 0.70 cutoff.
Not definitively on its own, but bronchodilator response helps. In asthma, FEV1 typically improves by ≥12% AND ≥200 mL after albuterol (significant reversibility). In COPD, improvement is usually less dramatic. However, some COPD patients show significant reversibility, and some asthmatics don't. Clinical history, imaging, and biomarkers (eosinophils, FeNO) help differentiate the two.
Repeat frequency depends on the clinical setting, disease being followed, and the testing protocol being used. The page is best used as a reference-value worksheet rather than as the source of the monitoring schedule itself.