Shock Index Calculator
Divide heart rate by systolic blood pressure to get the shock index and see where the result falls.
What it does
Shock index is a two number ratio: heart rate divided by systolic blood pressure. It was described in the 1960s as a quick bedside sign of circulatory strain and has returned to emergency and trauma practice because it uses readings that are already taken at triage. No extra equipment and no laboratory test are needed.
The usual adult reference is 0.5 to 0.7. A value of 0.9 is often used as the upper limit, and 1.0 or more is called the shock range. In a 2026 systematic review of prehospital trauma, an index above 0.9 was consistently linked with higher mortality, more transfusions and more critical care needs, although the review also found that a newer early warning score discriminated better overall.
The ratio adds something that neither reading says alone. Heart rate rises with pain, anxiety, fever and exercise, and systolic pressure can stay normal while the body compensates. Dividing one by the other means a pulse of 110 with a pressure of 100 shows up as 1.10, while the same pulse with a pressure of 130 shows up as 0.85. That difference is the point of the tool.
It is not a diagnosis and it is not universal. Beta blockers can keep the pulse low, a pacemaker can fix the rate, pregnancy changes the normal range, and trained athletes often sit at the low end. Children have their own age adjusted versions. Read the number with the trend, the symptoms and the medicines the person takes.
How to use
- Take the pulse and blood pressure at the same time, after the person has rested in the position used for the reading.
- Enter the heart rate in beats per minute.
- Enter the systolic pressure, which is the top number of the blood pressure reading.
- Read the index and the band.
- Repeat the reading if the first one is borderline, and compare it with earlier values.
- Treat a value of 1.0 or more, or a clear rise from the person's usual value, as a reason to seek clinical advice.
Formula
- Heart rate
- Resting pulse in beats per minute.
- Systolic pressure
- The top blood pressure number in mmHg.
- Shock index
- A unitless ratio, usually reported to two decimal places.
The division produces a unitless number, so the same index means the same thing whether the pressure was recorded in mmHg or converted from another unit. Report it to two decimals. A value on a band boundary can move with a single beat or a few mmHg, which is why one reading near 0.9 deserves a repeat rather than a label.
Worked example
Example: pulse 110 and systolic pressure 100
Defaults: heart rate 110 beats per minute and systolic blood pressure 100 mmHg.
- Divide the heart rate by the systolic pressure: 110 / 100 = 1.10.
- Compare with the adult reference: 1.10 is above the 0.9 upper limit.
- It is also at or above 1.0, so it falls in the shock range band.
- The reading is not near a boundary, so a repeat is unlikely to move it into a lower band.
- The tool shows a shock index of 1.10 and the band Shock range.
Reference table
| Shock index | Band | How to read it |
|---|---|---|
| Below 0.5 | Low | A slow pulse, a high systolic pressure, or both; check medicines and the person's usual range |
| 0.5 to 0.69 | Normal | The usual adult reference range |
| 0.7 to 0.89 | Borderline | Repeat the reading and look at the trend rather than one number |
| 0.9 to 0.99 | Elevated | The upper limit has been crossed; assess the person and the context |
| 1.0 or more | Shock range | Urgent review in context; the ratio alone does not prove shock |
Limits
- Not validated as a stand alone diagnosis, and a normal value does not rule out serious illness.
- Beta blockers, pacemakers and some antiarrhythmic drugs can hold the heart rate down and hide a rising index.
- Pregnancy, athletic training and age change the usual range, and children need age adjusted thresholds.
- The reading is only as good as the blood pressure technique and the timing of the two measurements.
Common mistakes
- Using the diastolic pressure instead of the systolic pressure in the denominator.
- Taking the pulse from a monitor and the pressure from a different moment, so the two numbers do not describe the same state.
- Treating a single borderline value as a trend when the next reading may be back inside the usual range.
- Applying the adult bands to a child without the age adjusted version.
- Reading a low index as reassuring in someone who takes a beta blocker or has a paced rhythm.
Try it yourself
Quick checks. Answers sit tucked under each question.
A resting pulse is 80 and the systolic pressure is 120. What is the shock index?
80 / 120 = 0.67, which falls in the normal band of 0.5 to 0.69.
A pulse of 130 with a systolic pressure of 90 gives what index and band?
130 / 90 = 1.44. That is at or above 1.0, so it is in the shock range band.
A pulse of 100 and a systolic pressure of 140 gives what index?
100 / 140 = 0.71, which is in the borderline band of 0.7 to 0.89.
Questions
What is a normal shock index?
For most adults the usual range is 0.5 to 0.7, and 0.9 is often used as the upper limit. Values of 1.0 or more are called the shock range.
Why is shock index used in trauma?
It combines two vital signs that are already measured at triage and can rise before the systolic pressure falls dramatically. Studies link an elevated index with worse outcomes, although it works best alongside other assessment tools.
Can shock index be high without shock?
Yes. Pain, anxiety, fever, exercise, anemia and some drugs can raise the pulse or lower the pressure. The index flags strain; it does not identify the cause.
Can shock index be normal in someone who is very ill?
Yes. Beta blockers, pacemakers and spinal injury can keep the pulse low, and young people can compensate for a long time. A normal ratio is not a guarantee.
Does pregnancy change the normal range?
Yes. Pregnancy changes blood volume and vascular resistance, and studies report a wider range in the postpartum period. Use obstetric reference values when they apply.
What should I do with a reading of 1.0 or more?
Treat it as a reason to seek urgent clinical advice, especially with bleeding, dizziness, confusion, chest pain or breathlessness. The number supports a decision; it does not make one.
Sources
- Shock index predicts clinical outcomes in stroke, Journal of the American Heart Association, PubMed
- Normal range of obstetric shock index in the postpartum period, PubMed
- Prehospital shock index and early warning score in adult trauma: systematic review, PubMed