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Calculate base excess (BE) using the Siggaard-Andersen formula. BE < −3 metabolic acidosis, > +3 metabolic alkalosis. HCO₃⁻ auto-calculated from pH + PaCO₂ if omitted. Derived from Siggaard-Andersen 1974, Cornell PICU, Medscape, and Langer 2022. Not medical advice.
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Fill in the form, run the tool, and review the result in one place.
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Tool usage guide
The Base Excess Calculator estimates the metabolic component of an acid-base disturbance from arterial pH, PaCO₂, and optional measured HCO₃⁻. It uses the Siggaard-Andersen formula, classifies the result as metabolic acidosis, normal, or metabolic alkalosis, and can calculate HCO₃⁻ from pH and PaCO₂ when HCO₃⁻ is omitted. This tool is not medical advice.
Background
An arterial blood gas shows pH 7.20, PaCO₂ 25 mmHg, and HCO₃⁻ 10 mmol/L.
Problem
The clinician needs to quantify the metabolic component of the acid-base disturbance.
How to use
Enter pH 7.20, PaCO₂ 25, HCO₃⁻ 10, and select 1 decimal place.
{"ph":7.2,"paco2":25,"hco3":10,"decimalPlaces":1}Outcome
The calculator returns BE = −16.1 mmol/L and classifies the result as severe metabolic acidosis.
Background
A blood gas has pH 7.40, PaCO₂ 40 mmHg, and HCO₃⁻ 24 mmol/L.
Problem
The student wants to verify whether the metabolic component is within the usual BE range.
How to use
Enter pH 7.40, PaCO₂ 40, HCO₃⁻ 24, and select 1 decimal place.
{"ph":7.4,"paco2":40,"hco3":24,"decimalPlaces":1}Base excess estimates the metabolic component of an acid-base disturbance, separate from the respiratory component.
A BE below −3 generally indicates metabolic acidosis or a base deficit.
A BE above +3 generally indicates metabolic alkalosis.
No. Entered HCO₃⁻ is optional; when omitted, it is calculated from pH and PaCO₂.
PaCO₂ is entered in mmHg, while HCO₃⁻ and base excess are reported in mmol/L.
Outcome
The calculator returns BE = −0.4 mmol/L, classified as a normal metabolic component.
Background
The report provides arterial pH and PaCO₂ but does not include a measured HCO₃⁻ value.
Problem
The clinician needs a BE estimate without manually calculating bicarbonate first.
How to use
Enter the available pH and PaCO₂ values, leave HCO₃⁻ blank, and choose the required decimal precision.
Outcome
The calculator derives HCO₃⁻ from pH and PaCO₂, then uses it to calculate and classify base excess.