How to measure blood oxygen on an Apple Watch

2 min read · 7 steps · Updated 2 October 2026

Blood oxygen is the share of red blood cells that carry oxygen. The watch estimates it with light from the sensor on its back. Apple states that the readings are for general fitness and wellness and are not intended for medical use.

These steps are for recent versions of watchOS. The pictures are simplified diagrams of the watch screen, not screenshots.

Step by step

1. Check the requirements

   You need an Apple Watch Series 6 or later or any Apple Watch Ultra. The app is not on the Apple Watch SE and not on a watch set up for a child. You must be at least 18, and the app must be offered in your country or region.

   Done

2. Set it up

   On the iPhone, open the Health app and follow the prompt to set up Blood Oxygen. If no prompt appears, tap Browse, Respiratory, Blood Oxygen. The app then appears on the watch.

   Done

3. Check the fit

   The watch should be snug but comfortable, with the back flat against the skin. If the wrist bone gets in the way, move the watch a little higher up the arm.

   Done

4. Rest your arm

   Sit down and put your arm on a table or in your lap, palm down, with the watch facing up. Keep the wrist flat.

   Done

5. Tap Start and hold still

   Open the Blood Oxygen app and tap Start. The measurement takes 15 seconds. Do not move or talk until it is done.

   Done

6. Read the result

   The watch shows a percentage. Tap Done. All readings are stored in the Health app on the iPhone under Browse, Respiratory, Blood Oxygen.

   Done

7. Decide about background readings

   The watch also measures by itself now and then when you are not moving, including at night. Under Settings, Blood Oxygen on the watch you can switch these off during Sleep Focus and in Theater Mode, where the red light could be annoying.

   Done

Good to know

A reading can fail or be off when the skin is cold, with tattoos under the sensor, when you move, or with a heart rate above 150 beats per minute at rest.

Do not use the watch to judge an illness. If you are short of breath or feel unwell, get medical help, whatever number the watch shows.

The same advice for a good sensor contact applies to the pulse: Apple Watch heart rate not accurate: 7 things to check.

Also on the watch: how to take an ECG on an Apple Watch.

In short: Series 6 or later, set up in Health, snug fit, arm resting, Blood Oxygen app, Start, 15 seconds still, results in Health under Respiratory.