Blood Oxygen Level Guide
Understand your blood oxygen (SpO2) readings.
Learn what normal, low, and critical oxygen levels mean.
SpO2 Assessment
Blood oxygen saturation (SpO2) measures the percentage of hemoglobin in your blood that is carrying oxygen.
Normal SpO2 ranges:
| SpO2 Level | Status | Action Needed |
|---|---|---|
| 95–100% | Normal | No action needed |
| 90–94% | Below normal | Monitor closely |
| 85–89% | Low | Seek medical attention |
| Below 85% | Critically low | Emergency - call 911 |
Factors that affect SpO2:
- Altitude: SpO2 naturally decreases at higher elevations
- Sea level: 95–100%
- 5,000 ft (1,500 m): 92–97%
- 8,000 ft (2,400 m): 90–95%
- 10,000 ft (3,000 m): 87–92%
- Exercise: May temporarily drop during intense activity
- Sleep: Slight dips are normal during deep sleep
- Smoking: Can lower baseline SpO2
- Cold fingers: May give inaccurate pulse oximeter readings
Using a pulse oximeter:
- Place it on your index or middle finger
- Keep your hand still and warm
- Wait 10–15 seconds for a stable reading
- Nail polish can interfere with readings