Enter the partial pressure of oxygen in arterial blood and the fraction of inspired oxygen into the calculator to determine the Pao2/Fio2 ratio. This calculator can also evaluate any of the variables given the others are known.

## Pao2/Fio2 Ratio Formula

The following formula is used to calculate the Pao2/Fio2 ratio.

Ratio = PaO2 / FiO2

Variables:

- Ratio is the Pao2/Fio2 ratio PaO2 is the partial pressure of oxygen in arterial blood (mmHg) FiO2 is the fraction of inspired oxygen (decimal)

To calculate the Pao2/Fio2 ratio, divide the partial pressure of oxygen in arterial blood by the fraction of inspired oxygen.

## What is a Pao2/Fio2 Ratio?

The PaO2/FiO2 ratio, also known as the P/F ratio, is a calculation used in medicine to assess the severity of hypoxemia, or low blood oxygen levels, in individuals with respiratory conditions such as acute respiratory distress syndrome (ARDS) or pneumonia. It is calculated by dividing the partial pressure of oxygen in arterial blood (PaO2) by the fraction of inspired oxygen (FiO2). A normal P/F ratio is typically above 300, and a lower ratio indicates a greater severity of hypoxemia.

## How to Calculate Pao2/Fio2 Ratio?

The following steps outline how to calculate the Pao2/Fio2 Ratio.

- First, determine the partial pressure of oxygen in arterial blood (PaO2) in mmHg.
- Next, determine the fraction of inspired oxygen (FiO2) as a decimal.
- Next, gather the formula from above: Ratio = PaO2 / FiO2.
- Finally, calculate the Pao2/Fio2 Ratio.
- After inserting the values for PaO2 and FiO2 into the formula, calculate the result.

**Example Problem:**

Use the following variables as an example problem to test your knowledge:

PaO2 (mmHg) = 80

FiO2 (decimal) = 0.4