Dissolved Oxygen Saturation
Calculate the saturation concentration of dissolved oxygen in water based on temperature and salinity, and determine the percent saturation of a measured DO sample.
Dissolved Oxygen Saturation
intermediateCalculate DO saturation concentration and percent saturation
Formula
DO_sat = f(temp, salinity)
How It Works
Dissolved oxygen solubility decreases with increasing temperature and salinity. This calculator uses the APHA (American Public Health Association) empirical formula to compute saturation concentration.
DO_sat = 14.652 − 0.41022T + 0.007991T² − 0.000077774T³ − S × 0.006
% Saturation = Measured DO / DO_sat × 100
Example
Freshwater at 20°C has a DO saturation of ~9.1 mg/L. If you measure 7.0 mg/L:
DO_sat(20°C, 0 PSU) = 9.1 mg/L
% Saturation = 7.0/9.1 × 100 = 76.9%
Frequently Asked Questions
What is a healthy DO level for aquatic life?
For most fish, DO should be above 5 mg/L or >80% saturation. Levels below 3 mg/L stress fish, and below 2 mg/L is lethal for most species.
Why does salinity affect DO?
Dissolved salts occupy space in water, reducing the available volume for oxygen molecules. Seawater at 35 PSU holds about 20% less oxygen than freshwater at the same temperature.