Oxygen saturation (SpO2)
Oxygen level of the blood in percent, usually measured with a fingertip pulse oximeter
Also known as
Definition
Oxygen saturation describes how much oxygen your blood is carrying, expressed as a percentage. It is usually measured painlessly with a pulse oximeter: a clip, typically on your fingertip, shines light through the skin, a sensor evaluates it, and after a few seconds the device shows your saturation and pulse. Many smartwatches and rings also display an SpO2 value.
| Parameter | Value |
|---|---|
| Unit | % |
| Reference Range | Typical for adults: 95–100%. With lung diseases such as COPD or at higher altitude, somewhat lower values may be considered acceptable. Your doctor can tell you which values are right for you. |
Agree on your personal target range with your doctor.
↓ What a low value means
Too little oxygen in the blood is called hypoxemia; according to MedlinePlus, the longer it lasts, the higher the risk of damage to tissues and organs. Lower values can be linked to conditions such as COPD, asthma, pneumonia or heart failure, to sleep apnea, or to being at higher altitude. Single low readings can also be measurement errors, for example with cold fingers. MedlinePlus gives this orientation: contact your doctor at 92% or lower, and seek immediate medical help at 88% or lower, as well as with bluish lips, shortness of breath or chest pain.
↑ What a high value means
Values up to 100% are within the typical range. A high reading does not reliably rule out problems, though: according to MedlinePlus, pulse oximeters can read 2 to 4 percentage points above or below the actual oxygen level, and darker skin pigmentation is one of the factors that can distort the result. For a more accurate value, your doctor can order an arterial blood gas test.
When to test
SpO2 is measured during routine checkups, with shortness of breath, lung or heart disease, sleep apnea, before, during and after surgery, and during oxygen therapy. For more reliable readings: no dark nail polish or artificial nails on the measuring finger, and keep your hands warm. Poor circulation and tobacco use can also distort the result.
Frequently asked questions
How accurate is a pulse oximeter? +
According to MedlinePlus, pulse oximetry readings can differ from the actual blood oxygen level by 2 to 4 percentage points. An arterial blood gas test from a blood sample is more accurate; sometimes both methods are combined.
What can distort the reading? +
Dark nail polish and artificial nails can block the light. Darker skin pigmentation, poor circulation, cold skin and tobacco use can also lead to inaccurate results.
How reliable are SpO2 readings from smartwatches and rings? +
They also measure optically and are therefore prone to interference, for example with cold skin or poor circulation. Treat single readings as estimates. If low values keep recurring or you notice symptoms such as shortness of breath, talk to your doctor.
Is a value below 95% always a concern? +
Not necessarily. With lung diseases such as COPD or at higher altitude, lower values may be considered acceptable. Your doctor determines which range fits you. At 88% or lower, MedlinePlus advises seeking immediate medical help.
Oxygen saturation (SpO2)
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.