Arterial Blood Gas Calculator
Arterial blood gas calculator works out Primary acid-base disorder and Expected compensation from What to compute, pH and PaCO2. The default figures on this page give primary acid-base disorder of Metabolic acidosis; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
7 steps
- pH 7.24 against the reference 7.40 +/- 0.02: acidaemia.
- PaCO2 24 mmHg, HCO3 10 mmol/L. Primary disorder: Metabolic acidosis.
- Winters: expected PaCO2 = 1.5 x 10 + 8 = 23 +/- 2 mmHg
- Measured PaCO2 24 lies inside the expected 21-25: appropriate compensation, no second disorder implied.
- Anion gap = Na - (Cl + HCO3) = 140 - (100 + 10) = 30 mmol/L.
- Albumin is 4.0 g/dL, so no correction is needed.
- Henderson-Hasselbalch check: 6.1 + log10(10 / (0.03 x 24)) = 7.243.
Its 6 worked examples are re-run on every release, last on 15 September 2026. What changed
Sources and references
5 sources
What the arterial blood gas calculator calculates
Interprets an arterial blood gas: identifies the primary acid-base disorder, computes the expected compensation and flags a superimposed second disorder, calculates the anion gap with albumin correction and the delta-delta, and works the alveolar gas equation, A-a difference, P/F ratio, arterial oxygen content and oxygenation index.
How to use this arterial blood gas calculator
Enter What to compute, pH, PaCO2 and Bicarbonate (HCO3-). Primary acid-base disorder updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Primary acid-base disorder, Expected compensation and Is the compensation appropriate?.
The method follows Berend K, de Vries APJ, Gans ROB. Physiological approach to assessment of acid-base disturbances, Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis, Figge J, Jabor A, Kazda A, Fencl V. Anion gap and hypoalbuminemia, ARDS Definition Task Force. Acute respiratory distress syndrome: the Berlin definition and West JB. Respiratory Physiology: The Essentials - the alveolar gas equation and oxygen carriage.
Diabetic ketoacidosis with appropriate respiratory compensation example
With What to compute: interpret, pH: 7.24, PaCO2: 24, Bicarbonate (HCO3-): 10, the calculator returns Primary acid-base disorder: Metabolic acidosis, Anion gap: 30, Albumin-corrected anion gap: 30. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Primary acid-base disorder, Expected compensation and Is the compensation appropriate?. The inputs you can vary are What to compute, pH, PaCO2, Bicarbonate (HCO3-), Sodium and Chloride.
Understanding Primary acid-base disorder, Expected compensation and Is the compensation appropriate?
An arithmetic aid to reading a blood gas, not an interpretation of a patient. Compensation formulas are empirical population rules with wide bands, laboratory reference ranges differ between analysers, and a normal-looking gas can hide two opposing disorders. Clinical interpretation belongs to a clinician with the patient in front of them.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
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Frequently asked questions
How to calculate arterial blood gas?
Interprets an arterial blood gas: identifies the primary acid-base disorder, computes the expected compensation and flags a superimposed second disorder. Open “How this is worked out” beside the result to see each step for your own figures.
What is the formula for calculating arterial blood gas compensation?
Interprets an arterial blood gas: identifies the primary acid-base disorder, computes the expected compensation and flags a superimposed second disorder. On this page it is computed from What to compute, pH and PaCO2 and shown as Primary acid-base disorder, Expected compensation and Is the compensation appropriate?.
What is the normal range for arterial blood gas levels?
On the figures this page opens with — pH 7.24, paCO2 24 mmHg, bicarbonate (HCO3-) 10 mmol/L and sodium 140 mmol/L — the primary acid-base disorder is Metabolic acidosis. No single number fits everyone: change any figure above and the answer updates as you type, with each step of the arithmetic beside it.
What information do I need for the arterial blood gas calculator?
You need What to compute, pH, PaCO2, Bicarbonate (HCO3-), Sodium, Chloride, Serum albumin and PaO2. The page opens with default figures that give primary acid-base disorder of Metabolic acidosis, so you can see the scale before entering your own.
What does this arterial blood gas calculator show?
It shows Primary acid-base disorder, Expected compensation, Is the compensation appropriate?, Anion gap, Albumin-corrected anion gap, Delta-delta, What the delta-delta says and pH implied by HCO3 and PaCO2, with the working and any warnings for your entries.
Can I check how the arterial blood gas calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.