SpO2 is a medical term used to measure the oxygen saturation level in the blood. It stands for "peripheral capillary oxygen saturation" and is measured using a pulse oximeter. The pulse oximeter is a small device that clips onto a finger and uses light to measure the amount of oxygen in the blood. The SpO2 level is expressed as a percentage and indicates how much oxygen is being carried by the red blood cells. A normal SpO2 level is between 95% and 100% .