pO₂ Unit Converter (mmHg to kPa)
pO₂ Unit Converter (mmHg to kPa)
Convert arterial pO₂ from mmHg to kPa — the commonest source of confusion when reading a blood gas from another country.
pO₂ Unit Converter (mmHg to kPa)
mmHg → kPapO₂ 95 mmHg
Formula
- 0.133322
- kPa per mmHg, from the definition 1 atm = 101.325 kPa = 760 mmHg
- reverse
- kPa × 7.50062 = mmHg
Worked example
pO₂ 95 mmHg
95 × 0.133322 = 12.67 kPa
pO₂ reference points
| mmHg | kPa | Meaning |
|---|---|---|
| 60 | 8.0 | Respiratory failure threshold |
| 80 | 10.6 | Lower limit of normal |
| 95 | 12.7 | Typical healthy adult, room air |
| 100 | 13.3 | Upper limit of normal |
Two units, one number
Blood gas oxygen tension is reported in millimetres of mercury in the United States and in kilopascals across most of Europe and much of the rest of the world. The conversion factor, 0.133322, follows directly from the definition of the standard atmosphere: 101.325 kPa equals 760 mmHg, so one millimetre of mercury is 0.133322 kilopascals, and one kilopascal is 7.50062 mmHg.
The practical risk is not doing the arithmetic wrong but not noticing the units need converting at all. A pO₂ of 8 looks unremarkable to someone expecting mmHg but represents severe hypoxaemia at 8 kPa — the conventional definition of type 1 or type 2 respiratory failure. The reverse mistake, reading a European result of 65 as if it were kPa, understates a genuinely low value. This confusion recurs whenever a patient, a paper, or a visiting clinician crosses between the two conventions, and it is worth a second glance at any blood gas number that looks unusually round or unusually low.
Normal arterial pO₂ on room air at sea level is roughly 80–100 mmHg (10.6–13.3 kPa) in a young adult, and falls gradually with age — a rough rule of thumb is that the lower limit of normal falls by about 1 mmHg per year past 60. Altitude lowers it independently of any lung disease, through the fall in atmospheric pressure.
Frequently asked questions
How do I convert pO₂ from mmHg to kPa?
Multiply by 0.133322. A pO₂ of 95 mmHg is 12.67 kPa. To convert kPa to mmHg, multiply by 7.50062.
What is a normal pO₂?
Roughly 80–100 mmHg, or 10.6–13.3 kPa, on room air in a young adult at sea level. The lower limit falls gradually with age.
What pO₂ defines respiratory failure?
A pO₂ below 8 kPa (60 mmHg) is the conventional threshold for respiratory failure, whether type 1 (with a normal or low pCO₂) or type 2 (with a raised pCO₂).
Does the US use mmHg or kPa for blood gases?
The United States reports in mmHg. Most of Europe, and many countries elsewhere, report in kPa. Always check which convention a given result uses before acting on it.
Related calculators
References
- Sasse SA, Jaffe MB, Chen PA. Arterial blood gas interpretation. In: StatPearls. StatPearls Publishing; 2024.
- BIPM. The International System of Units (SI), 9th edition — definition of the kilopascal and its relation to mmHg.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.