Normal Vital Signs Reference
Last updated: 5 July 2026
Reviewed by the Solved editorial team · Research and drafting assisted by AI
- The iconic 98.6°F (37°C) 'normal' body temperature was established by German physician Carl Wunderlich in the 1860s after millions of armpit readings — a 2017 Stanford study found the modern average has dropped to about 97.5°F (36.4°C).
- Pulse oximetry, the technology behind SpO2 readings, was invented in 1972 by Japanese engineer Takuo Aoyagi, who discovered he could measure blood oxygen by how light passes through a fingertip.
- The mercury thermometer that made temperature a standard vital sign was invented by Daniel Gabriel Fahrenheit in 1714 — the same man whose name now labels the Fahrenheit scale.
Vital Signs Reference
A vital signs reference page provides the clinical normal ranges for the five key measurements used by healthcare professionals to assess a patient's basic health status. It is used by nurses, paramedics, medical students, carers, and anyone wanting to understand health readings in context.
How to Use the Vital Signs Reference
- Locate the essential sign you want to check: blood pressure, heart rate, respiratory rate, temperature, or oxygen saturation.
- Find the normal range for the relevant age group.
- Compare the measured value against the normal range.
- Note whether the value is within range, slightly outside (borderline), or significantly outside (potentially critical).
- Use this reference as a guide only. Any concerning reading should be evaluated by a qualified healthcare professional.
The Formula
There are no single formulas for vital signs; each measurement has defined clinical reference ranges based on large population studies. The ranges are age-dependent and represent what is observed in healthy individuals at rest. Values outside these ranges are not automatically diagnostic but indicate the need for further assessment. Trends over time are often more informative than single readings.
Real-World Example
A nurse records the following for a 45-year-old patient at rest: blood pressure 128/84 mmHg; heart rate 76 BPM; respiratory rate 16 breaths per minute; temperature 37.1 degrees Celsius; oxygen saturation 97%. Interpretation: blood pressure is slightly high (stage 1 hypertension threshold is 130/80 mmHg); heart rate is normal; respiratory rate is normal; temperature is normal; oxygen saturation is normal. The slightly high blood pressure warrants monitoring and lifestyle discussion but is not immediately concerning in isolation.
Clinical Reference Ranges
Blood pressure in adults: normal is below 120/80 mmHg; high is 120 to 129 systolic with diastolic below 80; stage 1 hypertension is 130 to 139/80 to 89 mmHg; stage 2 hypertension is 140/90 mmHg or above; hypertensive crisis is above 180/120 mmHg.
Heart rate in adults at rest: normal is 60 to 100 BPM; bradycardia is below 60 BPM; tachycardia is above 100 BPM. Well-trained athletes commonly have resting heart rates of 40 to 60 BPM.
Respiratory rate in adults: normal is 12 to 20 breaths per minute; below 12 is bradypnoea; above 20 is tachypnoea.
Body temperature: normal oral temperature is 36.1 to 37.2 degrees Celsius (97 to 99 degrees Fahrenheit); fever is 38 degrees Celsius (100.4 degrees Fahrenheit) or above; hypothermia is below 35 degrees Celsius (95 degrees Fahrenheit).
Oxygen saturation (SpO2): normal is 95 to 100 percent; borderline is 92 to 94 percent; below 92 percent typically warrants supplemental oxygen and urgent assessment.
Frequently Asked Questions
What is a normal blood pressure for older adults? Blood pressure targets for older adults are sometimes set slightly higher by clinicians to account for reduced arterial elasticity and the risk of dizziness from over-treatment. Many guidelines suggest a systolic target below 130 mmHg for adults over 65, though individual circumstances vary significantly.
Why is oxygen saturation important? Oxygen saturation measures the percentage of haemoglobin in the blood carrying oxygen. Even small drops below 95 percent can indicate respiratory or cardiac problems. Persistent readings below 92 percent in a patient at rest suggest the body is struggling to maintain adequate oxygenation and require prompt medical evaluation.
Can a person have a normal heart rate but still have heart problems? Yes. A resting heart rate within the 60 to 100 BPM range does not rule out arrhythmias, structural heart disease, or coronary artery disease. An ECG and other investigations are needed to assess heart health beyond the rate alone.
What factors affect body temperature readings? Measurement site significantly affects temperature readings. Rectal temperatures are highest, followed by oral, then axillary (armpit). Time of day also matters; body temperature follows a circadian rhythm, being lowest in the early morning and highest in the late afternoon. Physical activity, eating, and ambient temperature all introduce variation.
Readings in both unit systems
Two of the five measurements are commonly recorded in a second unit, and the conversion is the step where a reading gets misread. Temperature in Fahrenheit follows from Celsius by multiplying by nine fifths and adding 32. Blood pressure in kilopascals follows from millimetres of mercury by multiplying by 0.1333224.
| Celsius | Fahrenheit | What the page's ranges call it |
|---|---|---|
| 35.0 | 95.00 | hypothermia, below the 35 Celsius line |
| 36.1 | 96.98 | the lower end of the normal oral range |
| 37.0 | 98.60 | mid normal, the usual reference value |
| 37.2 | 98.96 | the upper end of the normal oral range |
| 38.0 | 100.40 | fever, the published threshold |
| 39.0 | 102.20 | well above the fever line |
| 40.0 | 104.00 | at the top of the everyday scale |
| Blood pressure | Kilopascals | Category in the page's table |
|---|---|---|
| 120 over 80 | 16.00 over 10.67 | normal |
| 130 over 80 | 17.33 over 10.67 | stage 1 hypertension, systolic |
| 140 over 90 | 18.67 over 12.00 | stage 2 hypertension |
| 180 over 120 | 24.00 over 16.00 | hypertensive crisis threshold |
One arithmetic detail catches people out when comparing a home monitor with a chart. Measurement site moves the temperature reading before any conversion is applied: a rectal reading runs about 0.5 Celsius above an oral one and an axillary reading runs about 0.5 below, which is 0.9 Fahrenheit either way. A forehead or ear thermometer follows its own calibration again. Compare a reading against the column for the site it came from, and compare repeated readings from the same site against each other rather than across devices.
The published early warning bands
The five signs on this page are the inputs to the National Early Warning Score used across UK hospitals, which assigns a score of 0 to 3 to each observation and adds them. The bands below are the published ones for six of the seven parameters.
| Parameter | Score 3 | Score 2 | Score 1 | Score 0 |
|---|---|---|---|---|
| Respiratory rate | 8 or fewer, or 25 and above | 21 to 24 | 9 to 11 | 12 to 20 |
| Oxygen supply | not applicable | on supplemental oxygen | not applicable | breathing room air |
| Systolic blood pressure | 90 or fewer, or 220 and above | 91 to 100 | 101 to 110 | 111 to 219 |
| Pulse | 131 or more, or 40 or fewer | 111 to 130 | 91 to 110, or 41 to 50 | 51 to 90 |
| Consciousness | new confusion, responds to voice, responds to pain, or unresponsive | not applicable | not applicable | alert |
| Temperature | 35.0 or below | 39.1 or above | 36.0 or below, or 38.1 to 39.0 | 36.1 to 38.0 |
Two points about the table. The scoring system also scores oxygen saturation, on one of two scales depending on whether the patient is at risk of hypercapnic respiratory failure, and the saturation bands are not reproduced here because the chart consulted for this table did not carry them; a reader scoring a real patient should use the full chart. The aggregate score then pairs with published response thresholds, which are also on the chart rather than in this table.
Two observations scored
The worked example above this section gives a 45-year-old at rest with a blood pressure of 128 over 84, a heart rate of 76, a respiratory rate of 16, a temperature of 37.1 Celsius and saturation of 97 per cent. Scored over the six parameters in the table, every value falls in a zero band: 16 breaths is inside 12 to 20, a systolic pressure of 128 is inside 111 to 219, a pulse of 76 is inside 51 to 90, 37.1 Celsius is inside 36.1 to 38.0, the patient is alert and breathing room air. That is a total of 0 over those six parameters.
| Parameter | Reading | Score |
|---|---|---|
| Respiratory rate | 16 | 0 |
| Oxygen supply | room air | 0 |
| Systolic blood pressure | 128 | 0 |
| Pulse | 76 | 0 |
| Consciousness | alert | 0 |
| Temperature | 37.1 Celsius | 0 |
The six scores add to 0. Read as a snapshot the observation is unremarkable, which is what a total of zero is meant to convey.
A second patient shows how quickly the same six parameters separate. Respiratory rate 24, on supplemental oxygen, systolic pressure 95, pulse 118, new confusion, temperature 38.4 Celsius.
| Parameter | Reading | Score |
|---|---|---|
| Respiratory rate | 24 | 2 |
| Oxygen supply | supplemental oxygen | 2 |
| Systolic blood pressure | 95 | 2 |
| Pulse | 118 | 2 |
| Consciousness | new confusion | 3 |
| Temperature | 38.4 Celsius | 1 |
The six scores add to 12 out of a possible 18. The second patient reaches at least 2 on every parameter. That pattern is what the score is designed to surface: no single reading is extreme, and the aggregate moves anyway. A single parameter at 3, such as new confusion or a respiratory rate of 8, attracts the same attention on its own, which is why the chart lists a score of 3 in any one parameter as a trigger separate from the total.
Where the bands come from
The scoring bands in the table come from the National Early Warning Score 2 chart published by the Royal College of Physicians in 2017, which is the version the NHS recommends over the original score. The adult blood pressure categories on this page, normal, Elevated, stage 1, stage 2 and crisis, come from the 2017 guideline of the American College of Cardiology and the American Heart Association, which is also the source of the name given to a systolic reading of 120 to 129 with a diastolic below 80. The fifth vital sign group, saturation, is carried on the same early warning chart in the form of the two scales mentioned above.
Every range here describes adults at rest, and the page keeps to that scope deliberately. Population reference ranges shift with age, with pregnancy, with altitude and with chronic disease, and the early warning score was validated on adult inpatients rather than on children or on people at home. NICE guidance states that the score should not be used for children under 16 or for pregnant women, because the physiological response to illness differs in both groups. Treat the numbers as a way of reading a value in context, and take a concerning reading to a qualified clinician rather than to a chart.
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