Why use it

Guides safe and effective potassium repletion. Prevents under-dosing (persistent hypokalemia) and over-dosing (hyperkalemia). Practical conversion to common KCl preparations.

About

Estimates the amount of potassium chloride (KCl) needed to correct hypokalemia. A rough rule is that for each 0.3 mEq/L below 3.5, approximately 100 mEq of total body potassium deficit exists (in a 70 kg adult). This calculator provides dose estimates and practical administration guidance.

When to use

Serum K⁺ < 3.5 mEq/L
Symptomatic hypokalemia (weakness, arrhythmias, ECG changes)
Prophylactic supplementation (diuretic use, DKA recovery)

Formula

Estimated deficit (mEq) ≈ (3.5 - Current K) / 0.3 × 100 Practical approach: K 3.0-3.5: Give 40-80 mEq KCl K 2.5-3.0: Give 80-120 mEq KCl K < 2.5: Give 120-160+ mEq KCl (with cardiac monitoring)

Pearls & pitfalls

Each 10 mEq of K replaced raises serum K by approximately 0.1 mEq/L (transient).
Total body K deficit may be 200-400 mEq for each 1 mEq/L drop below 4.0.
ALWAYS check magnesium — hypomagnesemia causes refractory hypokalemia.
Max concentration: 40 mEq/L peripheral IV, 60 mEq/L central line.
Max IV rate with cardiac monitoring: 10-20 mEq/hr peripheral, up to 40 mEq/hr central.
Oral KCl is preferred when possible — better tolerated and steadier correction.
DKA: K may drop rapidly during insulin/fluid treatment — monitor every 1-2 hours.

Next steps

Give oral KCl if K ≥ 3.0 and asymptomatic. IV KCl if K < 3.0, symptomatic, or NPO. Max IV rate: 10-20 mEq/hr peripheral, 40 mEq/hr central (with cardiac monitoring). Recheck K⁺ after each 40-60 mEq given. Always check and correct Mg²⁺.

Evidence

Based on clinical practice guidelines and physiological estimates. Exact body K deficit is difficult to measure. Rule of thumb (100 mEq per 0.3 mEq/L deficit) is widely cited in clinical medicine textbooks and UpToDate.

References

Gennari FJ. Hypokalemia. N Engl J Med. 1998;339(7):451-458. — link

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