Blood Pressure Category Calculator

How it is calculated

The tool places one reading, in mmHg, into an American Heart Association (AHA) band. It tests from the most severe band downwards and stops at the first match. Hypertensive Crisis: systolic above 180 or diastolic above 120. Stage 2: systolic 140 or more, or diastolic 90 or more. Stage 1: systolic 130 to 139, or diastolic 80 to 89. Elevated: systolic 120 to 129 and diastolic under 80. Normal: systolic under 120 and diastolic under 80. Because the more severe test wins, one high number is enough to raise the category. Exactly 180 / 120 is still Stage 2.

Inputs that cannot be a real reading give no result: values of zero or below, systolic under 50 or diastolic under 20 (kPa values fall here), systolic above 300, diastolic above 200, or a diastolic that is not lower than the systolic. There is no band for low pressure, so 50 / 30 is shown as Normal. It classifies a single reading, not an average, and is not a diagnosis.

Common mistakes

• Swapping the two numbers. Systolic is the larger, first number (125) and diastolic the smaller, second one (82). Typing 82 / 125 now gives no result, because the diastolic must be lower than the systolic; swap them back.
• Looking only at the top number. A reading of 118 / 85 is Stage 1 because of the diastolic value, even though 118 alone would be Normal.
• Treating one reading as a diagnosis. The tool classifies the single pair you type; it does not average several readings or take cuff size and posture into account.
• Entering blood pressure in kPa or as a mean arterial pressure. The tool expects mmHg systolic and diastolic only; kPa values are far below any real reading in mmHg, so they give no result.
• Ignoring a Crisis result because the person feels well. Anything above 180 systolic or 120 diastolic is the top band, and the AHA treats it as needing medical attention.