🩺 Blood Pressure Converter
Convert blood pressure readings between mmHg, kPa, and cmH₂O. Includes the AHA/ACC blood pressure classification (normal, elevated, stage 1 & 2 hypertension, severe hypertension, and hypertensive crisis). Enter systolic and diastolic values to see the category instantly.
Understanding Blood Pressure Units
Blood pressure is traditionally measured in millimeters of mercury (mmHg), a unit that dates back to the mercury sphygmomanometer. In some countries and clinical settings, pressure may also be expressed in kilopascals (kPa) or centimeters of water (cmH₂O).
The standard conversion factors are:
- 1 mmHg = 0.133 kPa
- 1 mmHg = 1.36 cmH₂O
- 1 kPa = 7.5 mmHg
- 1 cmH₂O = 0.735 mmHg
These conversions are essential in clinical practice, particularly when comparing readings from different devices or when following international guidelines.
2025 AHA/ACC Blood Pressure Categories
The 2025 American Heart Association (AHA) / American College of Cardiology (ACC) guidelines classify blood pressure into the following categories:
- Normal: Systolic <120 mmHg and Diastolic <80 mmHg
- Elevated: Systolic 120–129 mmHg and Diastolic <80 mmHg
- Stage 1 Hypertension: Systolic 130–139 mmHg or Diastolic 80–89 mmHg
- Stage 2 Hypertension: Systolic ≥140 mmHg or Diastolic ≥90 mmHg
- Severe Hypertension: Systolic >180 mmHg and/or Diastolic >120 mmHg
- Hypertensive Crisis: Severe hypertension accompanied by symptoms such as chest pain, shortness of breath, or difficulty speaking — requires immediate medical attention.
The 2025 guidelines maintain the same thresholds as the 2017 guidelines, with a strong emphasis on prevention and early intervention through lifestyle modification and, when appropriate, medication.
Why Use This Converter?
- Instant conversion: Convert between mmHg, kPa, and cmH₂O in real-time.
- Clinical classification: See the 2025 AHA/ACC category for your blood pressure reading.
- Step-by-step breakdown: Understand exactly how the conversion is calculated.
- Free & private: No registration, no data storage — all calculations are done in your browser.
❓ Blood Pressure Converter FAQ
What is the normal blood pressure range?
According to the 2025 AHA/ACC guidelines, normal blood pressure is less than 120/80 mmHg (systolic <120 and diastolic <80).
What is considered high blood pressure?
Stage 1 hypertension is 130–139 mmHg systolic or 80–89 mmHg diastolic. Stage 2 hypertension is ≥140 mmHg systolic or ≥90 mmHg diastolic.
How do I convert mmHg to kPa?
Multiply the mmHg value by 0.133. For example, 120 mmHg × 0.133 = 15.96 kPa (≈16.0 kPa).
How do I convert kPa to mmHg?
Multiply the kPa value by 7.5. For example, 16 kPa × 7.5 = 120 mmHg.
What is cmH₂O used for?
cmH₂O (centimeters of water) is commonly used in respiratory therapy and mechanical ventilation to measure airway pressures. It is also occasionally used for blood pressure in some clinical contexts.
What is pulse pressure?
Pulse pressure is the difference between systolic and diastolic pressure. A normal pulse pressure is typically 30–50 mmHg. A wide pulse pressure (＞60 mmHg) may indicate arterial stiffness.
What is a hypertensive crisis?
A hypertensive crisis is a severe increase in blood pressure (＞180/120 mmHg) that can lead to a stroke or organ damage. If accompanied by symptoms like chest pain, shortness of breath, or difficulty speaking, seek emergency medical care immediately.
Is this converter accurate?
This converter uses the standard clinical conversion factors (1 mmHg = 0.133 kPa = 1.36 cmH₂O) for high accuracy. You can adjust the decimal precision to suit your needs.
Is this converter free?
Yes, this converter is completely free to use. No registration or personal data storage is required.
Can I use this for medical decisions?
No. This tool is for educational and informational purposes only. Always consult a qualified healthcare professional for medical advice, diagnosis, or treatment.