One mmol/L of potassium equals 3.91 mg/dL. To convert potassium from mmol/L to mg/dL, multiply the value by 3.91.
Potassium (K⁺) Calculator
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Potassium is one of the most important electrolytes in the human body. It plays a central role in nerve signaling, muscle contraction, and heart rhythm regulation.
Because of its importance, even small changes in potassium levels can have serious clinical consequences.
In many countries, potassium is reported in mmol/L. In others, it may be displayed in mg/dL. Understanding how to convert between these units helps prevent confusion when reviewing laboratory reports from different regions.
Understanding the Potassium Conversion Formula
The molecular weight of potassium (K⁺) is 39.1 g/mol. This determines the conversion factor between mmol/L and mg/dL.
Conversion formula: mg/dL = mmol/L × 3.91
For example: 4.0 mmol/L × 3.91 = 15.64 mg/dL
This simple multiplication gives you the equivalent value in mg/dL.
Why Potassium Levels Matter
Potassium is primarily found inside cells. It helps maintain electrical gradients that allow nerves and muscles to function properly. The heart is especially sensitive to potassium changes.
Low potassium (hypokalemia) may cause: – Muscle weakness – Fatigue – Abnormal heart rhythms
High potassium (hyperkalemia) may cause: – Palpitations – Dangerous cardiac arrhythmias – In severe cases, cardiac arrest
Because of these risks, potassium levels are routinely monitored in patients with kidney disease, heart conditions, or those taking certain medications such as diuretics.
Normal Reference Range
Typical serum potassium reference range: 3.5 to 5.0 mmol/L
Converted to mg/dL: 13.7 to 19.55 mg/dL
These ranges may vary slightly depending on the laboratory.
When Potassium Is Tested
Doctors commonly check potassium levels in: – Routine metabolic panels – Kidney function tests – Cardiac evaluations – Patients on ACE inhibitors or diuretics – Critical care monitoring
Accurate unit conversion ensures safe interpretation of results.
Clinical Interpretation Example
If a lab report shows: 5.8 mmol/L potassium
Converted: 5.8 × 3.91 = 22.68 mg/dL
This value is above the normal range and may require urgent medical evaluation depending on symptoms and ECG findings.
Common Causes of Abnormal Potassium
High potassium may occur due to: – Kidney failure – Certain blood pressure medications – Severe tissue breakdown – Dehydration
Low potassium may occur due to: – Vomiting or diarrhea – Diuretic use – Hormonal disorders – Poor dietary intake
Frequently Asked Questions
What is the conversion factor for potassium mmol/L to mg/dL?
Multiply mmol/L by 3.91.
Is potassium usually reported in mmol/L?
Yes. Most international laboratories report potassium in mmol/L.
Is mg/dL commonly used for potassium?
It is less common but may appear in certain regional laboratory reports.
What is 4.5 mmol/L potassium in mg/dL?
4.5 × 3.91 = 17.60 mg/dL.