Blood pH & Acid-Base Calculator

Calculate blood pH from PCO₂ and bicarbonate using the Henderson-Hasselbalch equation.

PCO₂ (mmHg) (mmHg)

Normal: 35-45 mmHg

HCO₃⁻ (mEq/L) (mEq/L)

Normal: 22-26 mEq/L

Expected compensation HCO₃⁻ or PCO₂ (mEq/L or mmHg)

Optional — to assess if compensation is adequate

Please check your inputs and try again.

Worked Examples

Example 1: Normal: PCO₂=40, HCO₃=24

pH = 6.1 + log(24/1.228)

Result: pH = 7.40 — Normal

Perfect acid-base balance

Example 2: Metabolic acidosis: PCO₂=28, HCO₃=14

pH = 6.1 + log(14/0.860)

Result: pH = 7.31 — Acidosis with respiratory compensation

HCO₃ low; PCO₂ low = compensating

Frequently Asked Questions

Henderson-Hasselbalch in blood?

Blood uses CO₂/HCO₃ buffer system: pH = 6.1 + log([HCO₃⁻]/[H₂CO₃]). H₂CO₃ ≈ 0.0307 × PCO₂. The lungs control PCO₂; kidneys control HCO₃.

Primary vs compensation disorders?

Primary: if pH<7.35 = acidosis, pH>7.45 = alkalosis. Respiratory: PCO₂ changes. Metabolic: HCO₃ changes. Compensation is always in the same direction as the primary disorder but never fully corrects pH.