Blood Pressure Calculator — Chart & Formula included
A blood pressure calculator compares your systolic (top number) and diastolic (bottom number) reading to standard categories so you can see if your result is normal, elevated, or high. Use this page to classify your numbers, review the chart, and understand the formula behind each result.
Quick summary
This blood pressure calculator classifies systolic and diastolic readings into standard categories, then shows pulse pressure and mean arterial pressure (MAP) to add context. The page includes a category chart, formulas, examples, and FAQs to help interpret a single reading and compare trends over time.
Blood Pressure Calculator
Use this blood pressure calculator to classify a single reading and identify your category. If you are tracking heart health trends, pair it with related calculators to keep habits consistent day to day.
Calculator
Enter your systolic and diastolic readings to classify your blood pressure category and view helpful supporting metrics.
Blood pressure chart
The chart below shows how systolic and diastolic numbers map to categories used in clinical guidance. If your readings fall across two categories, the higher category applies.
| Systolic (mmHg) | Diastolic (mmHg) | Category |
|---|---|---|
| Less than 120 | Less than 80 | Normal |
| 120-129 | Less than 80 | Elevated |
| 130-139 | 80-89 | High blood pressure (Stage 1) |
| 140 or higher | 90 or higher | High blood pressure (Stage 2) |
| Higher than 180 | Higher than 120 | Hypertensive crisis |
Blood pressure formula
Blood pressure is recorded as systolic over diastolic in millimeters of mercury (mmHg). Systolic is the pressure when the heart contracts, while diastolic is the pressure between beats.
These formulas help interpret a reading, but the trend over time is more important than any single measurement. Take multiple readings in a calm state and average them if you are monitoring progress.
Example calculation
Example: A reading of 128/78 mmHg has a systolic value between 120-129 and a diastolic below 80. That falls into the Elevated category. Pulse pressure is 50 mmHg (128-78), and MAP is about 95.0 mmHg.
If another reading is 136/86 mmHg, the diastolic value is in the 80-89 range, so the category becomes High blood pressure (Stage 1). Use this difference to see how small shifts can move a reading into a new category.
FAQ
How often should I check my blood pressure?
If you are monitoring trends, check at the same time each day for a week, then weekly. Pair readings with recovery tracking to compare rest and stress.
Why do my readings change during the day?
Hydration, caffeine, exercise, and stress can all raise or lower numbers. Rest quietly for five minutes and take two readings to reduce variability.
What if my systolic and diastolic fall in different ranges?
Use the higher category. For example, a reading of 118/82 is Stage 1 because the diastolic number is 80 or higher.
Does one high reading mean I have hypertension?
No. Diagnosis requires repeated measurements over time and sometimes ambulatory monitoring. Use the calculator for quick context, then talk with your clinician for next steps.
Resources
These sources explain blood pressure categories, measurement tips, and when to seek care.
Evidence-based references: American Heart Association, CDC: High Blood Pressure, NHLBI: High Blood Pressure.