Acid Base Calculator

How to use this acid – base calculator

What this calculator does

This calculator combines six laboratory values into a compact acid – base summary. It classifies the relationship among arterial pH, PCO₂, and Bicarbonate (HCO₃⁻), then calculates an Anion gap from sodium, chloride, and bicarbonate and an albumin-adjusted Corrected anion gap. The classification is a rule-based screening interpretation of the measured pattern; it does not determine the cause of an abnormality, establish whether a process is acute or chronic in every case, replace compensation formulas, or substitute for a clinician reviewing the full blood gas, electrolytes, symptoms, medications, and clinical history. The NCBI overview of arterial blood gas analysis explains why pH, PaCO₂, and bicarbonate must be interpreted together.

When to use it

It is useful for studying a blood-gas report, checking an anion-gap calculation by hand, comparing the uncorrected and albumin-corrected gap, or preparing a structured set of values for discussion with a qualified clinician. It can also help students see how respiratory and metabolic variables move in opposite or matching directions. It is not designed for emergency triage or self-treatment decisions.

How to calculate

1. The calculator opens with a complete demonstration set: pH 7.10, PCO₂ 56 mmHg, bicarbonate 24 mEq/L, chloride 108 mEq/L, sodium 140 mEq/L, and albumin 3.3 g/dL. Results and a validated example Excel workbook are available immediately.
2. Replace each demonstration value with values from the same laboratory snapshot. Plain decimal notation is accepted; scientific notation, unit text pasted into the field, and decimal-comma notation are rejected so ambiguous numbers are not silently reinterpreted.
3. Read the Acid – base pattern first, then the Anion gap and Corrected anion gap. The three header pills summarize whether pH, PCO₂, and HCO₃⁻ are below, within, or above the calculator's typical reference bands.
4. Use the table to compare each current value with its displayed reference band. The table updates from the same model used by the headline results.
5. Select Download Excel to export the current validated inputs and results as a real .xlsx workbook. Reset clears all six demonstration inputs and all calculated content; export is then disabled until a complete valid set is entered again.

Input guide

pH is required and unitless. Enter a decimal such as 7.10; this calculator accepts 6.50 – 8.00 as a broad technical input range. Lower values push the pattern toward acidemia and higher values toward alkalemia. A common mistake is treating a value inside 7.35 – 7.45 as proof that no acid – base disorder exists; compensation or mixed disorders can yield a near-normal pH.

PCO₂ is required in mmHg; enter a plain number such as 56. Values from 5 – 200 mmHg are accepted. Higher PCO₂ generally represents a stronger respiratory acidifying component, while lower PCO₂ represents a respiratory alkalinizing component. Do not paste “56 mmHg” into the field because the unit is already supplied by the interface.

Bicarbonate (HCO₃⁻) is required in mEq/L; 24 is a realistic example, and 1 – 60 mEq/L is accepted. Higher bicarbonate contributes a metabolic alkalinizing component; lower bicarbonate contributes a metabolic acidifying component. Blood-gas bicarbonate may be calculated rather than directly measured, so small differences from chemistry-panel total CO₂ can occur.

Chloride (Cl⁻) is required in mEq/L; the demonstration uses 108 and the accepted range is 50 – 150. Because chloride is subtracted in the anion-gap identity, a higher chloride lowers the calculated gap when sodium and bicarbonate are held constant. Use chloride from the same clinical context as the sodium and bicarbonate rather than mixing unrelated samples.

Sodium (Na⁺) is required in mEq/L; the example uses 140 and the accepted range is 100 – 180. Sodium is the positive term in the gap calculation, so raising sodium while the other values stay fixed raises the gap. Do not insert commas, unit labels, or scientific notation.

Albumin is required in g/dL; the example uses 3.3 and the accepted range is 0 – 6.5. Albumin is negatively charged and materially influences the usual anion gap, so lower albumin increases the correction added to the measured gap. Make sure the value is in g/dL rather than g/L; entering 33 instead of 3.3 would be a unit error and is outside the accepted range.

Output guide

Acid – base pattern is a categorical screening interpretation driven by pH, PCO₂, and HCO₃⁻. It can report normal, uncompensated, partially compensated, compensated, mixed, or discordant patterns. It is an interpretation aid rather than a diagnosis. The pH, PCO₂, and HCO₃⁻ header pills independently label each variable as low, typical, or high against 7.35 – 7.45, 35 – 45 mmHg, and 22 – 26 mEq/L.

Anion gap is a calculated identity in mEq/L: Na⁺ – (Cl⁻ + HCO₃⁻). This implementation displays 8 – 16 mEq/L as a commonly used orientation interval, but individual laboratories may use different intervals. A low or high result should therefore be interpreted against the reporting laboratory's own reference range and the full clinical picture. Corrected anion gap applies the reference-page model AG + 2.5 × (4.4 – albumin), with albumin in g/dL. It is an estimate intended to show how hypoalbuminemia can conceal an elevated uncorrected gap. The gap flag sentence describes the uncorrected gap's position relative to the 8 – 16 mEq/L orientation band.

The table columns Measure, Current value, Typical reference, and Flag are a structured restatement of the same model. “Current value” is the calculator value, “Typical reference” is an educational comparison band, and “Flag” is the low/typical/high interpretation. The corrected gap row is marked context dependent because albumin-adjusted thresholds should be interpreted with local laboratory practices.

Worked example

With the first-open values, pH 7.10 is below 7.35, PCO₂ 56 mmHg is above 45, and bicarbonate 24 mEq/L is within 22 – 26. The rule-based pattern is therefore Uncompensated respiratory acidosis. The anion gap is 140 – (108 + 24) = 8.00 mEq/L. Albumin is 3.3 g/dL, so the correction is 2.5 × (4.4 – 3.3) = 2.75, producing a corrected anion gap of 10.75 mEq/L. Those exact values appear in the first-render results, the comparison table, and the Excel workbook.

Learn more

The MSD Manual overview of acid – base disorders summarizes primary metabolic and respiratory disturbances and expected compensation. For a deeper discussion of measured and calculated blood-gas components, the NCBI arterial blood gas chapter describes common reference intervals and analytical limitations.