Normal Blood Oxygen Level: What It Is & How to Measure

Your blood oxygen level refers to the amount of oxygen circulating in your blood at any given time. It reflects how efficiently your body delivers oxygen from your lungs to your cells—a process essential for energy production, cellular repair, and organ function. Blood oxygen is most commonly measured through pulse oximetry, a non-invasive technology that provides a percentage known as SpO2.

Understanding what your blood oxygen level means, what's considered normal, and how to interpret changes can help you make more informed decisions about your health and performance.

What does blood oxygen level show?

The human body needs a constant supply of oxygen to function. We breathe it in through the nose and mouth, then our lungs transfer it into the bloodstream where it's distributed throughout the body. Oxygen is carried in your blood by red blood cells.

As it travels around the body, oxygen helps provide energy, replace worn out cells, and support internal organs and systems. Your blood oxygen level shows how much oxygen is being circulated by your red blood cells, and it's very closely regulated by your body. Keeping it within a specific range is necessary to ensure that all the cells in your body are getting enough oxygen.

The level of oxygen in your blood indicates how efficiently your body is dispersing oxygen from your lungs to your cells. Low levels can be a sign that there's something wrong with your lungs or blood circulation. If you've tested positive for COVID-19 and are experiencing symptoms, low blood oxygen levels may be a red flag that you're in need of medical attention.

How is blood oxygen measured?

Your blood oxygen level can be measured in two ways. The most accurate method is an arterial blood gas (ABG) test, an invasive procedure performed by a clinician that involves drawing blood directly from an artery. This test provides precise measurements but requires a medical setting and can be uncomfortable.

A more common and convenient method is pulse oximetry. This non-invasive technology is used by both medical-grade fingertip devices and wearables like WHOOP. Pulse oximetry works by shining light through the skin and measuring how much light is absorbed by your red blood cells.

Oxygenated hemoglobin and deoxygenated hemoglobin absorb light differently, allowing the device to calculate the percentage of your blood that is saturated with oxygen. This measurement is reported as SpO2, which stands for peripheral oxygen saturation. The process is quick, painless, and can be done continuously, making it ideal for tracking trends over time.

What is a normal blood oxygen level?

A normal blood oxygen level for most healthy individuals is typically between 95% and 100%. This range indicates that your lungs are effectively transferring oxygen into your bloodstream and that your circulatory system is delivering it efficiently throughout your body. A blood oxygen saturation (SpO2) level below 90% is generally considered low and is a condition known as hypoxemia.

Individual baselines can vary slightly. Some people may consistently measure at 97-98%, while others may be closer to 99-100%. What matters most is understanding your personal baseline and recognizing when your levels deviate significantly from that norm.

Causes and symptoms of low blood oxygen levels

Here are several potential symptoms of low blood oxygen levels:

• Heavy breathing or shortness of breath
• Chest pains
• Elevated heart rate and blood pressure
• Headaches and dizziness
• Restless feeling
• Confusion or loss of coordination
• Impaired vision
• Cyanosis

Low levels of blood oxygen can be caused by changes in your environment, most notably high-altitude conditions where there is less oxygen in the air. From a medical standpoint, a low SpO2 may be caused by anemia (insufficient red blood cells) or congenital heart diseases where the heart is unable to pump enough oxygenated blood. Additionally, lung ailments and things that decrease your body's ability to take in oxygen often lead to low blood oxygen levels as well, including:

• Asthma
• Bronchitis
• Sleep apnea
• Pneumonia
• COVID-19 or other viral infections
• Emphysema (when the lungs' air sacs are damaged, usually from smoking)
• Pulmonary edema (fluid buildup that causes lungs to swell) or fibrosis (lung tissue becomes scarred)

How to improve your blood oxygen level

While significant or persistent drops in blood oxygen require medical attention, certain lifestyle behaviors can help support healthy circulation and respiratory function. These actions can contribute to maintaining your levels within a normal range:

• Practice controlled breathing: Techniques like diaphragmatic (belly) breathing can help improve lung efficiency and oxygen intake.
• Stay hydrated: Proper hydration supports healthy blood flow, allowing oxygen to be transported more effectively throughout your body.
• Incorporate regular activity: Consistent cardiovascular exercise strengthens your heart and lungs, improving their ability to use oxygen.
• Eat iron-rich foods: Iron is a key component of hemoglobin, the protein in red blood cells that carries oxygen. Foods like spinach, lentils, lean meats, and fortified cereals can support healthy iron levels.
• Improve your posture: Sitting or standing upright allows your lungs to expand fully, which can improve oxygen intake.

If you notice consistently low readings or experience symptoms like shortness of breath, dizziness, or chest pain, consult a healthcare professional. These could be signs of an underlying condition that requires medical evaluation and treatment.

How WHOOP monitors your blood oxygen

While the most familiar pulse oximeters are those placed on your finger, the same technology is utilized in wearables like WHOOP to monitor blood oxygen levels from the wrist. WHOOP does this by sending two wavelengths of light (red and infrared) through your skin where it is absorbed and reflected by blood vessels. The red and infrared light each get absorbed differently by hemoglobin, and their absorption changes if the hemoglobin is oxygenated or not.

By comparing the relative amount of light that gets reflected back from each wavelength, WHOOP tracks what percentage of red blood cells are oxygenated. For example, if 96% are oxygenated and 4% are not, your SpO2 is 96%. WHOOP measures your blood oxygen level while you're sleeping at night, which allows for the most consistent and reliable readings.

Your SpO2 is reported each morning via the Health Monitor (available to members on WHOOP Peak and WHOOP Life plans). The Health Monitor tracks key vitals including live heart rate, resting heart rate, heart rate variability, respiratory rate, and skin temperature.

The WHOOP Health Monitor alerts you if blood oxygen levels or other key physiological metrics stray too far from their normal baseline.

Understand your body with WHOOP

Monitoring your blood oxygen provides a valuable window into your body's readiness and overall health. By understanding your personal baseline and seeing how it trends over time, you can make more informed decisions about your training, recovery, and daily habits. Blood oxygen is just one piece of a larger physiological picture that includes your biomarkers.

When combined with metrics like heart rate variability, respiratory rate, and sleep performance, it helps you build a complete understanding of how your body is responding to stress, strain, and rest. WHOOP gives you the tools to not just see your data, but to understand what it means and what to do next.

Frequently asked questions about blood oxygen

What is a normal oxygen level by age?

For healthy adults, a normal blood oxygen level is consistently between 95% and 100%, regardless of age. While certain health conditions that are more common in older adults—such as chronic obstructive pulmonary disease (COPD) or heart disease—can affect SpO2, age itself is not a primary factor in what is considered a normal range. If you have concerns about your oxygen levels as you age, discuss them with a healthcare provider who can assess your individual health profile.

Is 93% or 94% a good oxygen level?

A blood oxygen level of 93% or 94% is below the typical normal range of 95-100%. While a single reading in this range may not be a cause for alarm—especially if you're at high altitude or have a known respiratory condition—consistently low readings or readings accompanied by symptoms warrant a conversation with a healthcare professional. Context matters, so consider your baseline, activity level, and overall health when interpreting these numbers.

How can I raise my oxygen level quickly?

If you are experiencing a sudden drop in oxygen, remain calm and try some slow, deep breaths to improve lung function. Changing your position by sitting up straight or standing can also open your airways and improve circulation. However, these are temporary measures—if your levels are persistently low or you feel unwell, seek medical advice promptly.

The products and services of WHOOP are not medical devices, are not intended to diagnose COVID-19, the flu or any other disease, and should not be used as a substitute for professional medical advice, diagnosis or treatment. All content available through the products and services of WHOOP is for general informational purposes only.