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.
Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/