Clinical pressure units — mmHg, kPa and cmH₂O
1 mmHg = 0.1333 kPa = 1.36 cmH₂O. A 120 mmHg BP is 16.0 kPa. A 10 cmH₂O PEEP is 7.35 mmHg.
Clinical medicine runs on three pressure units simultaneously. The unit each device uses is not chosen for arithmetic convenience — it is historical. Fluency between them is a patient safety issue.
The exact factors
1 mmHg = 0.13332 kPa = 1.3595 cmH₂O > 1 kPa = 7.5006 mmHg = 10.197 cmH₂O > 1 cmH₂O = 0.09806 kPa = 0.7356 mmHg
Where each is used
mmHg: arterial and venous pressures, intraocular pressure, intracranial pressure. cmH₂O: airway pressures, PEEP, CPAP, CVP by water manometer. kPa: European ventilators, arterial blood gas partial pressures, some ICU monitors.
Worked example — PEEP misconversion
Ventilator PEEP prescribed at 10 cmH₂O = 7.4 mmHg = 0.98 kPa. If a device configured in mmHg is set to 10 (thinking cmH₂O), it delivers 13.6 cmH₂O — 36% above prescription and enough to trigger barotrauma in ARDS patients.
Recap
Airway → cmH₂O. Blood → mmHg. Europe → kPa. Convert before you compare.
Try the converters mentioned in this article
FAQ
Why does BP still use mmHg?+
Historical continuity — mercury sphygmomanometers set the reference and modern devices report the same units to preserve interoperability with clinical guidelines.
Is torr the same as mmHg?+
To six figures, yes. Modern SI-strict practice prefers torr because mmHg depends on mercury density and local gravity.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-07 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.