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Pressure (blood gas) mmHg → kPa

Convert pressure (blood gas) from mmHg to kPa

Sources last checked: 2026-11-03

Pressure (blood gas) mmHg → kPa

Convert pressure (blood gas) from mmHg to kPa

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Converts units only; reference ranges depend on the laboratory, the assay and the patient.

Source: NIST Special Publication 811 (2008), Guide for the Use of the International System of Units — Appendix B.8/B.9 conversion factors: 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 mmHg = 133.322 Pa, t/°C = (t/°F − 32)/1.8.Open

What is the Pressure (blood gas) mmHg → kPa?

Blood gas partial pressures (PaO₂, PaCO₂) are reported in kPa in the UK, Scandinavia and the Netherlands, and in mmHg in Germany, Austria, Turkey and the USA. This converter multiplies by 0.1333, following from 1 mmHg = 133.322 Pa (NIST SP 811). Blood pressure is almost universally kept in mmHg.

When to use it

  • Reading UK, Scandinavian or Dutch guidelines and blood gas reports in kPa
  • Calculating a P/F ratio or A–a gradient when the source formula or threshold is in kPa
  • Handover between ICUs that use different units

When not to use it

  • Ventilator pressures (PEEP, plateau pressure), which are given in cmH₂O or mbar
  • Blood pressure, where conversion to kPa is rarely useful in practice

How it is calculated

kPa = mmHg × 0.1333

Clinical pearls and limitations

  • Converts units only; reference ranges depend on the laboratory, the assay and the patient.
  • 1 mmHg = 133.322 Pa, so mmHg × 0.1333 = kPa; 1 kPa ≈ 7.50 mmHg.
  • A P/F ratio calculated with PaO₂ in kPa is about 7.5 times smaller than one with PaO₂ in mmHg; thresholds must be in the same unit.
  • The alveolar gas equation (A–a gradient) needs atmospheric pressure, water vapour pressure and PaCO₂ all in the same unit.
  • mmHg and Torr are equal for clinical purposes.

Frequently asked questions

How do I convert mmHg to kPa?

Multiply by 0.1333. Example: 40 mmHg × 0.1333 = 5.33 kPa; 100 mmHg × 0.1333 = 13.33 kPa.

Why do UK blood gases show kPa?

The UK, Scandinavia and the Netherlands adopted SI units for blood gases; the pascal is the SI unit of pressure.

Do I have to convert before calculating the P/F ratio?

Yes, if the threshold you compare against uses a different unit. Calculate in the unit of the definition you are applying.

Evidence and guidelines

  1. Primary source: NIST Special Publication 811 (2008), Guide for the Use of the International System of Units — Appendix B.8/B.9 conversion factors: 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 mmHg = 133.322 Pa, t/°C = (t/°F − 32)/1.8.
  2. BIPM. The International System of Units (SI), 9th edition, 2019 — Table 8 (non-SI units accepted for use with the SI, incl. litre) and the definition of the kelvin and degree Celsius.

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For healthcare professionals and medical students. These tools support, and do not replace, clinical judgement. Always check results against the original source and your local protocols.