Free USMLE Study Tools
Free calculators and the official lab values table for USMLE Step 1 study. Each tool shows its formulas, and every formula and reference value links to an official source you can check.
Lab values table
NBME Lab Values
Searchable table of the official USMLE laboratory reference ranges, with conventional and SI units.
Acid-base
Anion Gap Calculator
Anion gap, albumin correction, delta ratio and Winter’s formula.
Biostatistics
Sensitivity and Specificity Calculator
2×2 table: sensitivity, specificity, PPV, NPV, likelihood ratios, plus RR, OR, ARR and NNT.
Acid-base and respiratory
ABG Interpretation Calculator
Primary disorder, compensation check and A-a gradient for age.
How we build these tools
- Reference ranges come only from the official USMLE Laboratory Values table (usmle.org).
- Formulas and cutoffs come from NIH sources (StatPearls on NCBI Bookshelf, PubMed Central), linked under each formula.
- Every calculator is tested against the worked examples in those sources.
For exam study, not for clinical use.
Want questions to practise on? Try the free practice questions.