Oxygen Flow Rates and Percentages

The percentage of oxygen you are receiving from a given flow rate is not a precise science, but there are some guidelines you can rely on for a relatively accurate estimate.

Comparing the fraction of inspired oxygen (FiO2) in the air to a portable oxygen device is expressed as a percentage. The natural air we breathe contains 21% oxygen (21% FiO2) and 79% nitrogen at all times (with some trace gases). The FiO2 coming from a portable oxygen concentrator can vary anywhere from 90–96% FiO2. Hospital-grade oxygen found in a medical facility can reach >99% FiO2.

From these ranges, most oxygen concentrators can deliver >90% FiO2. However, that percentage drops substantially towards 21% FiO2 based on the flow rate you are using—in addition to a number of other factors. Those factors include breath size (how large or small a breath is), breath rate (how fast or slow you are breathing), and inspiratory flow rate (which is affected by both breath size and breath rate).

There are well-established percentages that are good rules of thumb when estimating your “effective FiO2” at home under normal conditions. Below is a overview of some typical flow rates (assuming a normal breath size and rate):

Oxygen Liters Per Minute and FiO2:

Understanding Oxygen Flow Rates and Percentages What percentage of oxygen is 1 liter per minute (LPM)?
At 1 LPM, the approximate FiO2 is 24%.

What percentage of oxygen is 2 LPM?
At 2 LPM, the approximate FiO2 is 28%.

What percentage of oxygen is 3 LPM?
At 3 LPM, the approximate FiO2 is 32%.

What percentage of oxygen is 4 LPM?
At 4 LPM, the approximate FiO2 is 36%.

What percentage of oxygen is 5 LPM?
At 5 LPM, the approximate FiO2 is 40%.

What percentage of oxygen is 6 LPM?
At 6 LPM, the approximate FiO2 is 44%.

What percentage of oxygen is 7 LPM?
At 6 LPM, the approximate FiO2 is 48%.

What percentage of oxygen is 8 LPM?
At 6 LPM, the approximate FiO2 is 52%.

What percentage of oxygen is 9 LPM?
At 6 LPM, the approximate FiO2 is 56%.

What percentage of oxygen is 10 LPM?
At 6 LPM, the approximate FiO2 is 60%.

Every increase by 1 LPM equates to a 4% increase in FiO2, starting from 24%. This easy rule of thumb gives you a safe estimate when approximating your “effective FiO2” at home based on your liter flow.