A–a Gradient Calculator
Alveolar–arterial oxygen difference with age-adjusted normals — locating the cause of hypoxaemia.
The gradient splits hypoxaemia in two: normal gradient means the lungs transfer fine and the problem is ventilation or altitude (opioid overdose, neuromuscular weakness); raised gradient means the lung itself — V/Q mismatch, shunt, fibrosis. It loses interpretive value on high FiO₂, where the expected gradient itself widens substantially.
Formula
Reference aid for healthcare professionals only. Every result must be independently verified before clinical use. Never use this tool for self-medication or to replace clinical judgement.
Alveolar–arterial oxygen difference with age-adjusted normals — locating the cause of hypoxaemia. The A–a Gradient Calculator is a free, private a-a gradient tool — every result computes instantly in your browser with no sign-up and no data upload.
About A–a Gradient Calculator
The gradient splits hypoxaemia in two: normal gradient means the lungs transfer fine and the problem is ventilation or altitude (opioid overdose, neuromuscular weakness); raised gradient means the lung itself — V/Q mismatch, shunt, fibrosis. It applies PAO₂ = FiO₂×(760−47) − PaCO₂/0.8; gradient = PAO₂ − PaO₂. Use the A–a Gradient Calculator to get an instant, clearly-explained result with the working shown step by step — free, private and with the source method cited.
How to use A–a Gradient Calculator
- 1Enter your details in the A–a Gradient Calculator input fields above.
- 2The result updates instantly with the working and reference bands shown.
- 3Adjust any value to explore how it changes the outcome — it's free and unlimited.
Why use A–a Gradient Calculator?
- ✓Instant a-a gradient result that recomputes as you type — no waiting, no page reloads
- ✓100% client-side: your health data never leaves your browser
- ✓Shows the actual formula and your numbers substituted in, so you can see exactly how the result is reached
- ✓Based on published, citable sources (Standard ABG physiology (West JB — Respiratory Physiology))
- ✓Free forever with no sign-up, account or app install
Frequently asked questions
How does the A–a Gradient Calculator work?+
The gradient splits hypoxaemia in two: normal gradient means the lungs transfer fine and the problem is ventilation or altitude (opioid overdose, neuromuscular weakness); raised gradient means the lung itself — V/Q mismatch, shunt, fibrosis. The calculation uses the formula: PAO₂ = FiO₂×(760−47) − PaCO₂/0.8; gradient = PAO₂ − PaO₂. Everything runs instantly in your browser as you type — your inputs are never uploaded.
Is the A–a Gradient Calculator accurate, and what is it based on?+
The method is traceable to authoritative sources: Standard ABG physiology (West JB — Respiratory Physiology). Results are estimates — individual variation always applies, so treat the output as a well-grounded starting point.
Is the A–a Gradient Calculator free and private?+
Yes. It's completely free with no sign-up, and all computation happens locally in your browser, so none of your health data ever leaves your device.
Can I use this for medical decisions?+
This is a reference aid for healthcare professionals and must be independently verified. It is not for self-diagnosis or self-medication.
What can I use the A–a Gradient Calculator for?+
It's commonly used for a-a gradient, alveolar arterial gradient, hypoxemia workup. Alveolar–arterial oxygen difference with age-adjusted normals — locating the cause of hypoxaemia.
Related Health tools
Adult BMI Calculator (WHO)
Body-mass index for adults with the WHO reference bands shown neutrally, plus the substituted formula step by step.
● LiveBMI Calculator (lb & inches)
US-style BMI from pounds and inches using the ×703 conversion, with CDC adult reference ranges.
● LiveBMI Calculator for Women
BMI with reference context written for women — what the index can and cannot say about female body composition.
● Live