Apple Health metrics › Blood Oxygen (SpO2)

Blood Oxygen (SpO2) on Apple Watch and iPhone

The percentage of oxygen carried in your blood, measured at the wrist.

What it is

Blood oxygen saturation shows how much of your hemoglobin is carrying oxygen. Most healthy people stay in a narrow, high band.

How Apple measures it

Supported Apple Watch models measure it with light sensors on the back of the watch, on demand and in the background. Availability depends on model and region, and Apple says it is not for medical use.

What's a normal range?

Healthy adults at sea level are usually 95 to 100%. Readings dip at altitude and can be noisy if the watch is loose or you move.

What moves it

• Altitude
• Watch fit and skin contact
• Cold hands or poor circulation
• Respiratory illness
• Sleep position

See Blood Oxygen (SpO2) next to your other vitals

Apple Health keeps this number several taps deep. OnlyVitals puts the metrics you pick, including Blood Oxygen (SpO2), on a single dashboard so you can read them at a glance. Everything stays on your device.

Frequently asked questions

What is a normal blood oxygen level on Apple Watch?

Typically 95 to 100% at sea level. Occasional lower readings can be sensor noise. Persistent low readings with symptoms need medical advice.

Can Apple Watch measure blood oxygen while I sleep?

On supported models, background readings are taken during the day and while you sleep, if the feature is on and the watch is worn snugly.

Related metrics

• Respiratory Rate
• Steps
• Sleep Duration
• REM Sleep
• Deep Sleep
• Core Sleep

This page is general information, not medical advice. Ranges vary by age, sex, fitness and device. Talk to a clinician about anything that worries you.