Oxygen Saturation Calculator (SpO₂ Levels)

Check SpO₂ — Oxygen Saturation Calculator

How to Use Oxygen Saturation Calculator (SpO₂ Levels)

1. Step 1: Prepare for a steady reading

   Sit still, warm your hands, remove nail polish on the measured finger, and wait 10–20 seconds for the value to stabilize.

2. Step 2: Measure SpO₂ on your oximeter

   Place the probe on a fingertip or earlobe and note the SpO₂ percentage displayed.

3. Step 3: Enter FiO₂ (optional)

   If on supplemental oxygen, enter the delivered FiO₂ (%). Otherwise leave 21% for room air.

4. Step 4: Tap Calculate

   Get your SpO₂ classification, S/F ratio, and estimated PaO₂ and P/F ratios.

5. Step 5: Add a note and save

   Optionally add a short note (e.g., after a walk) and save to your session log to track trends.

Key Features

• SpO₂ tracking
• Normal ranges
• Low value flags
• Notes

Understanding Results

Formula

To estimate PaO₂ from SpO₂, we use a simplified oxygen dissociation relation (Hill‑type) under standard conditions: PaO₂ ≈ P50 × (S / (1 − S))^(1/n), where S is saturation as a fraction (SpO₂/100), P50 ≈ 26.8 mmHg, and the Hill coefficient n ≈ 2.7. The S/F ratio is SpO₂ (%) divided by FiO₂ (as a fraction). The P/F ratio replaces SpO₂ with the estimated PaO₂.

Reference Ranges & Interpretation

At sea level, most healthy adults have SpO₂ of 95–100% at rest. Values of 90–94% are borderline and should be interpreted alongside symptoms and context. Below 90% (hypoxemia) is generally concerning. For P/F ratio, ≥300 is often considered normal oxygenation; 200–299 mild impairment, 100–199 moderate, and <100 severe impairment. Treat these as guides rather than diagnoses.

Assumptions & Limitations

Approximations assume normal temperature and pH and a typical hemoglobin curve. Fever, acidosis/alkalosis, anemia, hemoglobin variants, carbon monoxide exposure, motion, poor circulation, and device quality can all shift readings. If your result conflicts with how you feel or remains low, consult a clinician.

Complete Guide: Oxygen Saturation Calculator (SpO₂ Levels)

Check SpO₂ with the oxygen saturation calculator. Review typical saturation levels, understand when values may be low, and track readings over time. Easily.

Your oxygen saturation (SpO₂) is the percentage of hemoglobin in your blood that is carrying oxygen. Most healthy adults at sea level sit between 95% and 100% while resting. The oxygen saturation calculator on this page helps you record a reading, estimate related values (like an approximate arterial oxygen tension), and monitor your results over time with quick notes. It is built for clarity and mobile use, so you can check oxygenation quickly without digging through menus.

What is oxygen saturation?

Oxygen saturation represents the fraction of hemoglobin binding sites occupied by oxygen in arterial blood. When you seeSpO₂ on a pulse oximeter, that value is a non‑invasive estimate of arterial saturation using light absorption at two wavelengths. An SaO₂ measured from a blood sample is considered the reference standard, but for everyday use, a validated finger pulse oximeter is usually adequate for trend tracking at home. The value is a percentage: 98% means 98 of every 100 potential binding sites are carrying oxygen.

Saturation is not the same as oxygen content or oxygen delivery. Oxygen content also depends on hemoglobin concentration, and oxygen delivery depends on both content and blood flow (cardiac output). That’s why your oxygen saturation can be normal even if you feel winded during a hard workout—your muscles may need more oxygen delivery than your resting blood flow can supply.

How pulse oximeters work

A pulse oximeter shines red and infrared light through a fingertip or earlobe and measures how pulsatile arterial blood absorbs that light. Because oxygenated and deoxygenated hemoglobin absorb those wavelengths differently, the device can estimate the proportion that is oxygenated. Modern devices apply calibration curves embedded by the manufacturer. Accuracy is typically best between 90% and 100%. At low saturations and in poor perfusion, accuracy declines.

For the most reliable reading: sit still, warm your hands, remove nail polish on the measured finger, and wait 10–20 seconds for the value to stabilize. Cold hands, movement, and strong ambient light can all interfere with the signal.

Normal SpO₂ levels

At sea level, most healthy adults at rest have SpO₂ values between 95% and 100%. Brief dips during sleep or after exertion can occur. Values of 90–94% are considered borderline and should be interpreted in context, especially if you are at altitude, experiencing respiratory symptoms, or have chronic lung or heart conditions. Valuesbelow 90% (hypoxemia) are generally concerning and warrant clinical attention, particularly if persistent or associated with symptoms such as shortness of breath, chest discomfort, confusion, or cyanosis (a bluish color of the lips or fingertips).

At higher elevations, lower oxygen pressure reduces expected saturation. For example, a person acclimatized to 5,000–8,000 feet may show a resting saturation a few points lower than at sea level. Always assess symptoms and trends, not a single reading alone.

What affects readings

Several factors can skew or lower a pulse oximeter reading:

• Poor circulation from cold fingers or low blood flow.
• Motion artifact from talking, shivering, or walking.
• Nail polish or gel nails on the sensor finger.
• Ambient light or improper probe fit.
• Carbon monoxide exposure (carboxyhemoglobin) or methemoglobinemia.
• Skin tone and device quality; validated devices perform more consistently.

If a value looks unexpected, repeat after warming your hands, switching fingers, and remaining still for 20–30 seconds. Check that your device is placed correctly and fits snugly.

How to use the oxygen saturation calculator

Enter your SpO₂ (%) directly from your pulse oximeter. If you are breathing room air, FiO₂is 21%. If you are using supplemental oxygen, enter the approximate delivered FiO₂ from your setup. The calculator returns your SpO₂ classification (normal, borderline, or low), the S/F ratio (SpO₂ divided by fractional FiO₂), an estimated PaO₂ (an approximation of arterial oxygen tension), and an approximate P/F ratio (PaO₂ divided by FiO₂). You can also add a short note and save entries to a session log for quick trend review.

These derived values are informative but not diagnostic. They assume standard body temperature and pH and do not replace clinical measurements like an arterial blood gas when precision is required.

Formulas and estimates used

The calculator estimates PaO₂ from SpO₂ using a simplified Hill‑type relation for the oxygen dissociation curve under standard conditions:

PaO₂ ≈ P50 × (S / (1 − S))^(1/n), where S is saturation as a fraction (SpO₂/100), P50 ≈ 26.8 mmHg is the partial pressure at which hemoglobin is 50% saturated, and the Hill coefficient n ≈ 2.7. This relation produces stable, intuitive estimates across the clinically relevant 90–100% range. Values get very sensitive near 100%; we cap internal math slightly below 100% to avoid unrealistic spikes.

The S/F ratio is simply SpO₂ (%) divided by FiO₂ as a fraction. For example, 95% on room air (FiO₂ 0.21) gives an S/F of ~452. The P/F ratio uses the estimated PaO₂ instead of SpO₂. In many clinical settings, a P/F ratio ≥ 300 indicates normal oxygenation; 200–299 mild, 100–199 moderate, and < 100 severe impairment. These thresholds should be read in full clinical context.

Understanding S/F and P/F ratios

S/F is convenient when arterial blood gases are unavailable. It scales with oxygen delivery—higher is better. Because saturation flattens at the top of the curve, S/F loses resolution at very high saturations but becomes informative when SpO₂ drifts into the low 90s. A low S/F ratio suggests impaired oxygen transfer or ventilation‑perfusion mismatch but does not pinpoint the cause by itself.

P/F approximations from SpO₂ are helpful for triage and trending but remain approximations. Factors such as fever, acidosis, hemoglobin variants, anemia, or measurement artifact can shift apparent oxygenation without directly indicating gas exchange performance. Always pair ratios with symptoms and, when necessary, direct testing.

When low SpO₂ matters

Persistent SpO₂ below 90% at rest is generally concerning and should be assessed by a clinician. If you have shortness of breath, chest pain, confusion, or bluish lips/fingertips, seek urgent evaluation. If you live at high altitude or have a chronic lung condition, discuss personalized thresholds with your care team.

For a general introduction to pulse oximetry, see the NIH MedlinePlus overview (external). For oxygen therapy targets, many public resources suggest individualized goals based on underlying disease; your clinician’s advice should guide decisions.

Tracking trends at home

One reading rarely tells the full story. Using the session log in this oxygen saturation calculator, you can add brief notes such as “after a short walk” or “morning reading before coffee.” Over several days, patterns become clearer: lower numbers only after exercise may be expected, whereas steadily decreasing resting values deserve attention.

Pair your tracking with basic vitals: heart rate, breathing rate, and blood pressure. If you want to calculate or track those, explore our companion tools:

• Heart Rate Calculator — estimate zones and check recovery.
• Respiratory Rate Calculator — measure breaths per minute accurately.
• Blood Pressure Calculator — log and interpret BP readings.
• VO₂ Max Calculator — gauge aerobic fitness and oxygen use.
• Sleep Apnea Risk Calculator — screen risk factors for disordered breathing.

Helpful related tools

Hydration and recovery also influence how you feel at a given SpO₂. On days you train or spend time at altitude, consider checking your fluid intake with our Hydration Calculator and, if you are planning intervals or long easy miles, browse your Zone 2 Heart Rate to keep intensity where you expect it.

Finally, remember that a good night’s sleep positively affects daytime oxygenation for many people. If sleep quality is a goal, try our Sleep Efficiency Calculator to understand how much of your time in bed is truly restful.

Frequently Asked Questions