TidalPrep › Free tools
Free respiratory therapy calculators
Free respiratory therapy calculators for RT students and RRT exam prep, with textbook-standard formulas, worked examples, and sources. They are fast and run entirely in your browser.
ABG interpretation calculator
Enter pH, PaCO2, and HCO3 to classify an ABG as uncompensated, partially, or fully compensated, check expected compensation (Winter's formula and more), and calculate the anion gap.
RSBI calculator (rapid shallow breathing index)
Calculate the rapid shallow breathing index (f/VT) during a spontaneous breathing trial. Uses Yang and Tobin's threshold of 105, with formula, worked example, and sources.
P/F ratio calculator (PaOâ‚‚/FiOâ‚‚)
Calculate the PaO2/FiO2 (P/F) ratio and see the Berlin ARDS oxygenation category: mild, moderate, or severe. Formula, worked example, and sources included.
A–a gradient calculator (alveolar gas equation)
Calculate PAO2 with the alveolar gas equation and the alveolar-arterial (A-a) oxygen gradient, with the age-adjusted normal on room air. Formula, worked example, and sources.
Tidal volume by ideal (predicted) body weight
Calculate predicted (ideal) body weight with the ARDSNet formula and the 4, 6, and 8 mL/kg tidal volume targets for lung-protective ventilation. Formula, example, and sources.
Study aid only. Not for clinical decisions. This calculator teaches textbook formulas for exam prep. It is not a medical device and does not replace clinical judgment, your facility's protocols, or a licensed clinician's assessment. Nothing you enter leaves your browser.
Start free: 50 questions