Arterial Blood pH Calculator
Convert a hydrogen-ion concentration [H⁺] into blood pH using pH = −log₁₀[H⁺]. Enter the [H⁺] in moles per litre (M) and the calculator returns the pH. For reference, normal arterial blood pH sits in a tight range of about 7.35–7.45.
Rates and fees change frequently. Always confirm the current figures
with the official authority before relying on this result.
Formula
pH = −log₁₀[H⁺]
- pH is the negative base-10 logarithm of the hydrogen-ion concentration, so smaller [H⁺] means a higher (more alkaline) pH.
- Enter [H⁺] in moles per litre (M). Normal arterial blood has [H⁺] around 40 nmol/L (4 × 10⁻⁸ M), giving a pH near 7.40.
- Each whole-number drop in pH represents a tenfold rise in hydrogen-ion concentration.
- Blood pH is tightly regulated; values outside roughly 7.35–7.45 indicate acid-base disturbance and warrant clinical assessment.
Example: [H⁺] = 4 × 10⁻⁸ M
Inputs
- [H⁺] Concentration (M): 4e-8
A hydrogen-ion concentration of 4 × 10⁻⁸ M gives pH = −log₁₀(4 × 10⁻⁸) ≈ 7.40, right in the middle of the normal arterial range.
Frequently asked questions
How is blood pH calculated from [H⁺]?
Take the negative base-10 logarithm of the hydrogen-ion concentration: pH = −log₁₀[H⁺], with [H⁺] in moles per litre.
What is the normal arterial blood pH?
About 7.35 to 7.45. Below 7.35 is acidaemia and above 7.45 is alkalaemia.
What [H⁺] corresponds to a normal pH?
Roughly 40 nanomoles per litre, i.e. 4 × 10⁻⁸ M, which gives a pH close to 7.40.
Why is a small pH change important in blood?
Because pH is logarithmic, a change of just 0.3 pH units doubles or halves the hydrogen-ion concentration, which can have major physiological effects.
Is this a medical diagnosis?
No. It is a unit conversion for educational use. Interpreting acid-base status requires a full blood-gas analysis and clinical context.