Calculate predicted FVC, FEV1, and PEF from age, sex, height, and population reference context, then compare measured values in a spirometry-pattern worksheet.
Spirometry is the most common pulmonary function test, measuring how much air you can exhale (Forced Vital Capacity, FVC) and how quickly you can exhale it (Forced Expiratory Volume in 1 second, FEV₁). Comparing measured values to predicted normal values — based on age, sex, height, and ethnicity — is the fundamental method for diagnosing obstructive lung diseases (COPD, asthma) and restrictive lung diseases (pulmonary fibrosis, neuromuscular weakness).
Predicted values are derived from large population studies. The most widely used reference equations include NHANES III (Hankinson 1999) for the US, ECSC/ERS for Europe, and the newer GLI-2012 (Global Lung Initiative) reference that provides multi-ethnic z-scores. Ethnicity-specific correction factors are applied because lung volumes differ significantly across populations — African Americans have approximately 12% lower FVC than Caucasians of the same height and age, while Asians have approximately 6% lower values.
This calculator computes predicted FVC, FEV₁, FEV₁/FVC ratio, and peak expiratory flow (PEF) using the ECSC/ERS reference equations with ethnicity corrections. When measured spirometry values are entered, it calculates percent-predicted values, identifies the ventilatory pattern (obstructive, restrictive, normal, or mixed), and provides GOLD staging for obstructive patterns and ATS severity grading for restrictive patterns — with visual bar charts comparing measured to predicted.
Predicted spirometry values are only useful when they are read beside the measured maneuver and the rest of the pulmonary context. This page keeps the predicted numbers, percent-predicted values, and pattern summary together so the data are easier to review before formal interpretation with the full spirometry report.
Male: FVC = 5.76 × Height(m) - 0.026 × Age - 4.34 | FEV₁ = 4.30 × Height(m) - 0.029 × Age - 2.49 Female: FVC = 4.43 × Height(m) - 0.026 × Age - 2.89 | FEV₁ = 3.95 × Height(m) - 0.025 × Age - 2.60 Ethnicity correction: African American ×0.88, Asian ×0.94, Hispanic ×0.96 Obstructive: FEV₁/FVC < 70% | Restrictive: FVC < 80% predicted with normal ratio
Result: Predicted FVC 4.58 L (83% pred), FEV₁ 3.48 L (63% pred), FEV₁/FVC 57.9% — Obstructive pattern, GOLD 2 Moderate
Predicted FVC = 5.76 × 1.75 - 0.026 × 50 - 4.34 = 4.58 L. Measured FVC 3.8 L = 83% predicted (near normal). Predicted FEV₁ = 4.30 × 1.75 - 0.029 × 50 - 2.49 = 3.48 L. Measured FEV₁ 2.2 L = 63.2% predicted. FEV₁/FVC = 2.2/3.8 = 57.9% (< 70%). Pattern: Obstructive. GOLD 2 (FEV₁ 50-79% predicted).
Spirometry interpretation starts by comparing measured values with a predicted range derived from age, height, sex, and population reference data. That comparison is what makes the raw numbers clinically meaningful, because the same measured FEV1 can look normal for one person and clearly reduced for another.
An obstructive or restrictive-looking worksheet pattern does not replace full pulmonary-function interpretation. Bronchodilator response, lower-limit-of-normal thresholds, flow-volume loops, and in some cases lung volumes or diffusion capacity are still needed for a fuller picture.
This page uses a simplified percent-predicted and fixed-cutoff approach so the numbers are easy to review quickly. Modern spirometry interpretation increasingly favors LLN or z-score methods, especially at the extremes of age, so borderline results should be read cautiously.
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This calculator uses height-, age-, and sex-based spirometry prediction equations to estimate expected FVC, FEV1, and related values, then compares any entered measured values against that predicted range. It uses a simplified worksheet approach to flag whether the entered pattern looks obstructive, restrictive, mixed, or near-normal.
Because the page uses simplified reference equations and fixed cutoffs, it should be read as a review aid rather than as a replacement for a formal spirometry report with lower-limit-of-normal or z-score interpretation.
Thoracic cage dimensions, trunk-to-leg ratio, and total lung capacity vary across ethnic groups due to genetic and evolutionary factors. African Americans have relatively longer limbs and smaller thoracic volumes for the same height, resulting in lower lung volumes. The GLI-2012 reference uses multi-ethnic equations with ethnicity-specific coefficients to account for this.
The fixed 70% ratio can over-diagnose obstruction in the elderly (normal ratio declines with age) and under-diagnose in young adults. The GLI-2012 and ATS/ERS 2021 guidelines now recommend using the lower limit of normal (LLN, typically the 5th percentile z-score) rather than a fixed cutoff. This calculator uses the fixed 70% for simplicity, which remains standard in GOLD guidelines.
FVC is measured during forced (maximal effort) exhalation — it may be lower than SVC in patients with obstructive disease because forced exhalation causes airway compression. Slow VC is measured during relaxed exhalation. If SVC > FVC, it suggests air trapping from obstruction. True restrictive disease is confirmed by reduced total lung capacity (TLC) on body plethysmography.
Spirometry alone cannot — both show obstruction. However, significant bronchodilator reversibility (>12% and >200 mL improvement in FEV₁ after albuterol) favors asthma. COPD typically shows incomplete reversibility. Clinical history (age of onset, smoking, triggers, variability) is essential for differentiation.
PEF measures the maximum flow during forced exhalation and is effort-dependent. It is useful for asthma monitoring (variability >20% suggests uncontrolled asthma) but is not a substitute for full spirometry. PEF primarily reflects large airway function and can be normal in small airway disease.
Reference equations are derived from non-smoking populations. Smoking accelerates FEV₁ decline from the normal 25-30 mL/year to 50-80 mL/year. The calculator shows predicted values for healthy individuals — the gap between predicted and measured widens with cumulative smoking exposure (pack-years).