Bicarbonate mmol/L to mEq/L Converter
Convert a bicarbonate or total CO2 result between mmol/L and mEq/L using the one-to-one factor for the HCO3- ion, with the formula and report cautions shown next to the result.
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Converted Result
Because bicarbonate has one charge, the numeric value is the same in mmol/L and mEq/L.
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What This Bicarbonate Converter Is For
This page is for people who have a bicarbonate, HCO3-, total CO2 or CO2 content result and need the same number in the other common concentration unit. UK laboratory reports usually show bicarbonate in mmol/L. Some overseas reports, textbooks and clinical examples use mEq/L. For bicarbonate, the conversion is unusually simple: one millimole per litre is numerically equal to one milliequivalent per litre, because bicarbonate carries one negative charge.
The converter is most useful when you are copying results between an NHS patient portal, a private laboratory report, a hospital letter, a research table or a clinical calculator that asks for the other unit. It is not a medical interpretation tool. Bicarbonate values sit inside a wider acid-base picture that may involve pH, pCO2, sodium, potassium, chloride, kidney function, medicines, fluid loss, vomiting, diarrhoea, diabetes, respiratory illness and the way the sample was collected. A single converted unit cannot say what is happening in the body.
Bicarbonate Unit Formula
For a monovalent ion, milliequivalents per litre equal millimoles per litre multiplied by the absolute charge. Bicarbonate is written HCO3- and has an absolute charge of 1.
mEq/L = mmol/L x 1
mmol/L = mEq/L / 1
A result of 24 mmol/L therefore converts to 24 mEq/L. A result of 18 mEq/L converts to 18 mmol/L. Rounding should normally match the number of decimals on the original report rather than add extra precision.
Why The Same Number Appears
The word “equivalent” counts chemical combining capacity, so it depends on ionic charge. Calcium has a charge of 2+, so mmol/L and mEq/L are not the same for calcium. Bicarbonate has a single negative charge, so one millimole contains one milliequivalent. That is why this converter locks the factor at 1 instead of asking for a molecular weight or a custom factor.
Quick Bicarbonate Conversions
| mmol/L | mEq/L | How The Result Is Often Read On A Report |
|---|---|---|
| 18 mmol/L | 18 mEq/L | Below many adult reference intervals, but the printed lab interval and clinical context matter. |
| 20 mmol/L | 20 mEq/L | May be near a lower limit on some reports; do not compare it with a different lab’s interval. |
| 22 mmol/L | 22 mEq/L | Used by some laboratories as the lower adult reference boundary. |
| 24 mmol/L | 24 mEq/L | A common example value for checking the one-to-one conversion. |
| 29 mmol/L | 29 mEq/L | Used by some sources as an upper adult reference boundary. |
| 32 mmol/L | 32 mEq/L | Above many adult example intervals, but the converter still only changes units. |
Serum CO2, Total CO2 And Blood Gas Bicarbonate
Reports do not always use identical labels. A chemistry panel may say CO2, total CO2, TCO2, bicarbonate, bicarb or HCO3-. MedlinePlus explains that most CO2 in blood is present as bicarbonate, so a serum CO2 test is often treated as a measure of blood bicarbonate. Lab Tests Online UK also notes that bicarbonate is commonly measured with other electrolytes and may be used with blood gases when acid-base status is being assessed.
The collection route can matter. A routine chemistry sample is often venous serum or plasma. A blood gas may be arterial or venous and can include calculated bicarbonate alongside pH and carbon dioxide pressure. That difference is one reason a converter should not be used to decide whether two reports are clinically identical. It can change the unit label, but it cannot account for sample handling, analyser method, timing, oxygen or ventilation status, or the rest of the result set.
Worked Examples For Common Searches
Enter 24 and choose mmol/L to mEq/L. The result is 24 mEq/L. The row beside the result will show the reverse check, so you can confirm that 24 mEq/L returns to 24 mmol/L.
Choose mEq/L to mmol/L and enter 18. The answer is 18 mmol/L. If your report prints a lower limit, enter it as a separate interval check rather than using a copied internet range.
With one decimal place, 29.4 mmol/L becomes 29.4 mEq/L. With zero decimals, the display rounds to 29 mEq/L. The stored calculation still uses the typed number.
How To Use The Optional Interval Boxes
The low and high boxes are there for record checking, not diagnosis. If your report says 22-29 mmol/L, enter 22 and 29. Because the conversion factor is one-to-one, the same numeric interval also applies after converting to mEq/L. The scale below the main answer then places your typed number within that interval. If your report has no interval, or if it uses an age-specific, pregnancy-specific, hospital-specific or blood-gas-specific interval, leave the boxes blank unless you can copy the exact limits from the same report.
Reference intervals vary. Oxford University Hospitals lists an adult bicarbonate interval of 22-29 mmol/L on its test catalogue, while MedlinePlus gives an example range of 23-29 in both mEq/L and mmol/L and states that ranges can vary among laboratories. That is not a contradiction for the purpose of unit conversion. It is a reminder that the conversion and the clinical interpretation are separate tasks.
When This Converter Should Not Be Used Alone
- Do not use it to decide whether you have acidosis, alkalosis, kidney disease, lung disease, dehydration or any other condition.
- Do not use it to change medication, fluids, bicarbonate supplements or treatment plans.
- Do not compare an arterial blood gas result with a routine serum result as if they were collected and calculated in the same way.
- Do not use a reference interval from another country or another lab if your report already prints one.
- Seek medical help promptly if a result is flagged and you feel unwell, or if your clinician has asked you to act on a blood test result.
Related Acid-Base And Electrolyte Unit Checks
| Related Value | Why It Is Often Nearby | Unit Caution |
|---|---|---|
| Sodium | Often reported in the same electrolyte profile as bicarbonate. | mmol/L and mEq/L are also numerically equal for sodium because the charge is 1+. |
| Potassium | Useful in many acid-base and kidney reviews. | mmol/L and mEq/L are numerically equal for potassium because the charge is 1+. |
| Chloride | Used with bicarbonate in anion gap calculations. | mmol/L and mEq/L are numerically equal for chloride because the charge is 1-. |
| Calcium | May appear on wider chemistry panels. | Do not assume a one-to-one factor for calcium; charge and reporting form matter. |
| pH and pCO2 | Blood gases use these values to assess acid-base balance. | They are not converted by this page and need their own clinical context. |
FAQ
Is 1 mmol/L bicarbonate always 1 mEq/L?
For bicarbonate HCO3-, yes. The ion has one negative charge, so the numeric concentration is the same in mmol/L and mEq/L. The label changes; the number does not.
Why does my US report use mEq/L while my UK report uses mmol/L?
Laboratory unit habits vary by country, hospital system and software. UK reports commonly use mmol/L for electrolytes. Some US educational material and reports use mEq/L. For bicarbonate, both show the same numeric value.
Can this tell me if my bicarbonate result is normal?
No. It can compare your number with an interval you type, but it cannot judge normality. The same value may be read differently depending on sample type, lab method, age, illness, medicines and other results.
Is serum CO2 the same as bicarbonate?
Serum total CO2 mostly reflects bicarbonate, which is why the labels are often linked. It is still best to use the wording on the report and ask the requesting clinician if the sample type or method matters.
How many decimals should I use?
Match the report unless you have a reason to show more. If a report gives 24, show 24 mEq/L. If it gives 24.3, one decimal place is usually enough for a unit copy.
Why are calcium or magnesium conversions not one-to-one?
mEq/L depends on ionic charge. Bicarbonate, sodium, potassium and chloride have a charge magnitude of one. Calcium and magnesium often have a charge magnitude of two, so their mEq/L relationship is different.
Sources
- MedlinePlus. (2025). CO2 Blood Test. U.S. National Library of Medicine. https://medlineplus.gov/ency/article/003469.htm
- Lab Tests Online UK. (n.d.). Bicarbonate. Lab Tests Online UK. https://labtestsonline.org.uk/tests/bicarbonate
- Oxford University Hospitals NHS Foundation Trust. (2025). Bicarbonate. Oxford University Hospitals. https://www.ouh.nhs.uk/biochemistry/tests/tests-catalogue/bicarbonate/
- Regenstrief Institute. (2024). The Unified Code for Units of Measure. UCUM. https://ucum.org/ucum
- National Institute of Standards and Technology. (n.d.). SI Units: Amount Of Substance. NIST. https://www.nist.gov/pml/owm/si-units-amount-substance