Bicarbonate Unit Converter
Bicarbonate Unit Converter
Convert bicarbonate between mmol/L, mEq/L and mg/dL. Bicarbonate is monovalent, so mmol/L and mEq/L are the same number — the harder question is which bicarbonate your report means.
Bicarbonate converter
Monovalent — mmol/L = mEq/LBicarbonate 24 mmol/L
Formula and conversion factors
mg/dL = mmol/L × 6.102
mEq/L = mmol/L (bicarbonate is monovalent)
- 0.163891
- 10 ÷ 61.02, the formula mass of HCO₃⁻ (H 1.008 + C 12.011 + 3 × O 15.999)
- mEq/L
- bicarbonate carries a single negative charge, so millimoles and milliequivalents are the same number
- total CO₂
- what the chemistry analyser measures on a venous sample; it includes dissolved CO₂ and carbamino compounds and runs about 1–2 mmol/L above calculated bicarbonate
- calculated bicarbonate
- what a blood gas analyser reports — derived from measured pH and pCO₂ by the Henderson-Hasselbalch equation, not measured directly
Worked example
Bicarbonate 24 mmol/L
24.0 mmol/L — the unit almost every laboratory reports, whether labelled bicarbonate, total CO₂ or TCO₂
24.0 mmol/L = 24.0 mEq/L — bicarbonate is monovalent, so the two are the same number
24.0 ÷ 0.163891 = 146.4 mg/dL, a mass unit not used on serum reports
Within the adult reference interval of 22–29 mmol/L
Thresholds across the units
| mmol/L | mEq/L | mg/dL | |
|---|---|---|---|
| Adult reference interval | 22 – 29 | 22 – 29 | 134 – 177 |
| Metabolic acidosis | < 22 | < 22 | < 134 |
| Severe — usually needs urgent assessment | < 15 | < 15 | < 92 |
| Metabolic alkalosis | > 29 | > 29 | > 177 |
Three different bicarbonates
| Reported as | How it is obtained | What to remember |
|---|---|---|
| Total CO₂ (TCO₂) | Measured directly on the chemistry analyser from a venous sample | Includes dissolved CO₂ and carbamino compounds, so it runs about 1–2 mmol/L above the calculated figure |
| Actual (calculated) bicarbonate | Derived by the blood gas analyser from measured pH and pCO₂ | Not measured at all; it inherits any error in pH or pCO₂, including a delayed or air-contaminated sample |
| Standard bicarbonate | Calculated at a pCO₂ of 5.3 kPa, 37°C and full oxygenation | Strips out the respiratory contribution, isolating the metabolic component |
Which bicarbonate is on the report?
Bicarbonate is reported in mmol/L in the United Kingdom and in mEq/L in the United States, and the two are the same number, because bicarbonate carries a single negative charge. The mg/dL column converts by 10 ÷ 61.02, the formula mass of HCO₃⁻, or 0.1639 mmol/L per mg/dL, and exists only for older literature. The genuinely useful question on this analyte is not which unit but which bicarbonate the report means.
Three exist. Total CO₂ is measured directly on a chemistry analyser from a venous sample and includes dissolved carbon dioxide and carbamino compounds, so it reads about 1 to 2 mmol/L above the alternative. The actual bicarbonate on a blood gas report is not measured at all: it is calculated from pH and pCO₂ by the Henderson-Hasselbalch equation, and inherits any error in either. Standard bicarbonate is the same calculation performed at a normal pCO₂, which removes the respiratory contribution.
A low bicarbonate is the earliest and cheapest signal of a metabolic acidosis, and it is often the abnormality that arrives first on a routine profile. The next step is always the anion gap, which separates lactate, ketones, renal failure and toxins from the hyperchloraemic causes; then Winters’ formula, which says what pCO₂ the respiratory system should have reached. A pCO₂ away from that predicted value means a second, coexisting disorder.
A high bicarbonate is either a metabolic alkalosis or the renal compensation for a chronic respiratory acidosis, and the two are told apart by the pH. Where it is a primary alkalosis, a urinary chloride below about 20 mmol/L identifies the saline-responsive causes — vomiting, nasogastric aspiration, recent diuretics — while a higher value points towards mineralocorticoid excess or ongoing diuretic use. Hypokalaemia both causes and is caused by alkalosis, so the two are corrected together.
Frequently asked questions
Is mmol/L the same as mEq/L for bicarbonate?
Yes. Bicarbonate is monovalent, so one millimole carries one milliequivalent of charge and the two figures are identical. A bicarbonate of 24 mmol/L is 24 mEq/L, and no conversion should be applied.
How do I convert bicarbonate from mg/dL to mmol/L?
Multiply by 0.1639, which is 10 divided by the formula mass of HCO₃⁻, 61.02. A value of 146 mg/dL is 23.9 mmol/L. To go the other way, multiply the mmol/L figure by 6.102.
Why does my blood gas bicarbonate differ from the laboratory one?
They are different measurements. The laboratory reports total CO₂, measured directly and including dissolved CO₂, which runs about 1 to 2 mmol/L higher. The blood gas figure is calculated from pH and pCO₂ rather than measured, and inherits any error in those.
What is standard bicarbonate?
Bicarbonate calculated at a pCO₂ of 5.3 kPa, 37°C and full oxygenation. Holding pCO₂ at a normal value removes the respiratory contribution, so standard bicarbonate reflects the metabolic component of an acid-base disturbance alone.
Can bicarbonate be normal in an acid-base disorder?
Yes. A mixed disorder in which a metabolic acidosis and a metabolic alkalosis coexist can leave bicarbonate in range, and the anion gap and delta ratio are what reveal it. Bicarbonate should always be read with pH and pCO₂.
Related calculators
References
- Berend K, de Vries APJ, Gans ROB. Physiological approach to assessment of acid-base disturbances. N Engl J Med. 2014;371(15):1434–1445.
- Kraut JA, Madias NE. Serum anion gap: its uses and limitations in clinical medicine. Clin J Am Soc Nephrol. 2007;2(1):162–174.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.