CalculatorMint

PFT Calculator (USA) — GLI-2012

Calculate FEV1, FVC, and FEV1/FVC predicted values, Z-scores, LLN, and obstruction severity using GLI-2012 reference equations. Free for clinicians, researchers, and students.

Sex (biological)
Height unit (USA default: inches)
GLI-2012 ethnicity (USA labs)

Choose the GLI group that matches how your U.S. lab or EHR codes ancestry. Mixed or unlisted ancestry usually uses “Other / mixed.”

Leave blank to compute the ratio from FEV1 ÷ FVC. Enter a lab-reported ratio (%) if you want to match the report exactly.

Spirometry patternNonspecific pattern (FEV1 low; ratio and FVC ≥ LLN)
Obstruction severity
No obstruction (FEV1/FVC ≥ LLN)
Height used
177.8 cm
FEV1 Z-score
-1.67
FEV1/FVC Z-score
-0.30
GLI-2012 predicted, % predicted, LLN, and Z-scores
IndexMeasuredPredicted% predLLNZ
FEV13.20 L4.08 L78.5% · <LLN3.21 L-1.67
FVC4.10 L5.13 L79.9%4.05 L-1.57
FEV1/FVC78.0%79.9%97.7%69.3%-0.30
  • FEV1/FVC was calculated from volumes (3.2 ÷ 4.1 = 78%).
  • Predicted values, LLN, and Z-scores use GLI-2012 (Quanjer et al.) equations for FEV1, FVC, and FEV1/FVC.
  • LLN corresponds to the 5th percentile (Z ≈ −1.645). Values below LLN are flagged as abnormal for screening.
  • Obstruction severity follows ATS/ERS 2005 bands based on FEV1 % predicted when FEV1/FVC is below LLN.
  • Restriction cannot be confirmed on spirometry alone — low FVC with a normal ratio suggests possible restriction; TLC is required for confirmation.
  • Educational tool only. Not a substitute for accredited PFT software, quality review, or clinical judgment.

How this USA PFT calculator works

  1. Enter age (3–95), sex, height (inches or cm), and the GLI-2012 ethnicity group used in U.S. labs.
  2. Enter measured FEV1 and FVC in liters (optional FEV1/FVC % if you want to match a report).
  3. Review predicted mean, % predicted, LLN, Z-score, pattern label, and ATS/ERS obstruction severity when the ratio is below LLN.

GLI-2012 equations (overview)

GLI-2012 models each index with an LMS framework (lambda, mu, sigma) so predicted values and Z-scores stay continuous across childhood and adulthood:

Z = ((measured / M)^L − 1) / (L × S)% predicted = (measured / M) × 100LLN ≈ 5th percentile (Z ≈ −1.645)

Height is converted to centimeters internally. U.S. users can enter height in inches (default).

Obstruction severity (ATS/ERS 2005)

When FEV1/FVC is below the LLN, severity is graded by FEV1 % predicted:

  • Mild — FEV1 ≥ 70% predicted
  • Moderate — 60–69%
  • Moderately severe — 50–59%
  • Severe — 35–49%
  • Very severe — < 35%

PFT calculator FAQ

What does this PFT calculator compute?

It uses GLI-2012 reference equations to estimate predicted FEV1, FVC, and FEV1/FVC, percent predicted, lower limit of normal (LLN), Z-scores, a spirometry pattern label, and ATS/ERS 2005 obstruction severity when the ratio is below LLN.

Why GLI-2012 for USA use?

Many U.S. pulmonary labs and guidelines have moved toward Global Lung Function Initiative (GLI) equations instead of older NHANES III–only norms. GLI-2012 covers ages 3–95 and includes ethnicity-specific coefficients used in U.S. practice.

What Z-score means below the LLN?

The LLN is the 5th percentile, corresponding to a Z-score of about −1.645. A Z-score below −1.645 is conventionally treated as below the normal range for that index.

Can this diagnose restriction?

No. A low FVC with a normal FEV1/FVC suggests possible restriction, but total lung capacity (TLC) is required to confirm a restrictive defect. This tool is for educational spirometry interpretation only.

Is this a medical device or clinical decision support?

No. CalculatorMint provides free educational calculations for clinicians, researchers, and students. It is not FDA-cleared software, does not replace accredited PFT systems, and is not medical advice.

Read more: How to interpret PFTs with GLI-2012 in the USA.

Medical disclaimer: CalculatorMint provides educational spirometry math only. It is not a medical device, does not provide diagnosis or treatment advice, and must not replace clinician judgment or accredited pulmonary function testing systems.