Two Number Languages for the Same Heartbeat
In 1896, Scipione Riva-Rocci wrapped an inflatable cuff around an arm and read the pressure by how high it pushed a column of mercury — hence millimeters of mercury, mmHg. The unit was born inside the instrument, and American medicine never let go of it. When mercury was phased out of clinical use for toxicity in the 2000s, most of Europe converted its charts to the SI unit kilopascal. The result: the same patient can be "120/80" in one country and "16.0/10.7" in another, and both numbers are equally correct. The conversion that makes them identical is this page's job, and it is exact — mmHg is defined through the density of mercury and standard gravity, both fixed by the 2019 SI redefinition.
kPa = mmHg × 0.133322387415
1 mmHg = 133.322387415 Pa
Defined: mercury density (13,595.1 kg/m³) × standard gravity (9.80665 m/s²) — exact, no uncertainty.
Blood Pressure Readings, Translated
| mmHg | kPa | Clinical meaning |
|---|---|---|
| 90/60 | 12.0/8.0 | Low end of normal. |
| 120/80 | 16.0/10.7 | The classic healthy reading. |
| 130/85 | 17.3/11.3 | Elevated — watch it. |
| 140/90 | 18.7/12.0 | Hypertension threshold (WHO/ESC). |
| 160/100 | 21.3/13.3 | Stage 2 — treatment territory. |
Notice the hypertension threshold: 140/90 mmHg lands on 18.7/12.0 kPa — figures that look like completely different numbers but define the same clinical line. That is the whole reason this page exists: a patient's electronic record can be exported in one unit and read in another, and a 2 kPa rounding error on a cuff's internal transducer is a 15 mmHg mistake on the chart. Automated cuffs measure pressure in Pa internally and convert to whichever unit the market wants — the transducer does this exact multiplication thousands of times per clinic day.
Engineering Context
The reverse direction is kPa to mmHg, used by vacuum and weather work. mmHg is the same physical scale as mmHg to Pa and Pa to mmHg on the pressure hub, while the SI-native conversions are kPa to psi and psi to kPa for the American gauge side. Torricelli's original vacuum barometer — the ancestor of every cuff — measured the same column; see torr to Pa and Pa to torr for that lineage. The full family lives in the pressure hub.
More: kPa to mmHg · mmHg to Pa · kPa to psi · Pressure Hub
Related Unit Converters
Frequently Asked Questions
How do I convert mmHg to kPa?
Multiply by 0.133322387415: kPa = mmHg × 0.133322. The classic blood pressure reading 120/80 mmHg becomes 16.0/10.7 kPa. The factor is exact — it comes from the density of mercury and standard gravity, both defined.
Is 120 over 80 mmHg a normal pressure in kPa?
Yes — 120/80 mmHg is 16.0/10.7 kPa, and it is the same healthy reading in both units. Normal is often quoted as 'below 120/80' in mmHg or 'below 16/10.7' in kPa. The WHO and ESC publish thresholds in both units because different countries' hospitals use different conventions.
Why does the US use mmHg while Europe uses kPa for blood pressure?
The sphygmomanometer — the blood pressure cuff — was invented in 1896 measuring millimeters of mercury directly against a mercury column, and US medicine never switched. Most of Europe moved to the SI unit kPa in the 1970s when mercury columns were retired from clinical use. Both units measure the same pressure; the conversion is exact and this page is the bridge.
More: kpa to mmhg · mmhg to pa · kpa to psi · Pressure Hub