Blood Oxygen Level (SpO2) Calculator
Estimate blood oxygen saturation levels and understand SpO2 readings.
Learn what normal, low, and critical oxygen levels mean.
SpO2 Assessment
Blood Oxygen Saturation (SpO2) measures the percentage of hemoglobin molecules in your blood that are carrying oxygen. A pulse oximeter measures this non-invasively by shining light through your fingertip.
Normal SpO2 Ranges:
| SpO2 Level | Classification |
|---|---|
| 95–100% | Normal |
| 90–94% | Below Normal (consult doctor) |
| Below 90% | Low (seek medical attention) |
| Below 85% | Critical (emergency) |
Factors that affect SpO2 readings:
- Altitude: At higher elevations, lower air pressure means less oxygen. At 5,000 ft (1,524 m), readings of 92–95% may be normal.
- Activity level: During intense exercise, SpO2 may temporarily drop by 1–3%.
- Nail polish: Dark nail polish can interfere with pulse oximeter readings.
- Cold fingers: Poor circulation from cold temperatures can give inaccurate readings.
- Skin pigmentation: Some pulse oximeters may read slightly differently on darker skin tones.
When to seek help:
- If your resting SpO2 consistently reads below 94%, consult your doctor.
- If it drops below 90%, seek medical attention promptly.
- Sudden drops of more than 3–4% from your baseline warrant attention.
Heart rate and SpO2 together give a more complete picture. A normal resting heart rate for adults is 60–100 bpm. If SpO2 is low AND heart rate is elevated, your body may be compensating for low oxygen.
Tip: Take readings while sitting calmly. Wait at least 10 seconds for the reading to stabilize. Take 3 readings and use the most consistent value.