Tool · free
Water oxygen saturation calculator (% saturation)
Enter the water temperature and the measured oxygen concentration, and the calculator returns the percent saturation and the concentration corresponding to full saturation (100%) under those conditions. Optionally include altitude and salinity.
Enter at least the water temperature.
How we calculate
The oxygen saturation concentration at 1 atm is derived from the Benson-Krause equation (adopted in the APHA standard and by the USGS) - a function of temperature in kelvin. For brackish waters we subtract a salinity-dependent correction, and pressure (from altitude or entered directly) corrects the result, accounting for water vapour pressure.
Percent saturation is simply the ratio of the measured value to the saturation concentration: % = measured oxygen / oxygen at 100% × 100. The result is indicative - probe calibration and thermometer accuracy translate directly into the outcome.
Frequently asked questions
What does oxygen saturation above 100% mean?
Supersaturation (>100%) occurs during the day in waters with intense algal and plant photosynthesis - they produce oxygen faster than it can escape to the atmosphere. Values well below 100% (undersaturation) indicate oxygen consumption, e.g. during the breakdown of organic matter; very low saturation means a risk of oxygen depletion (fish kill).
Why is temperature needed?
Oxygen solubility in water depends strongly on temperature - cold water holds more. So the same concentration (mg/l) means a different percent saturation at 5°C than at 25°C. The calculator computes the saturation concentration for the given temperature (Benson-Krause equation).
Do I have to enter altitude and salinity?
No. By default we calculate for fresh water at sea level (1 atm). At higher altitudes pressure drops and the saturation concentration falls, so for mountains it is worth entering the altitude. Salinity lowers oxygen solubility - relevant for brackish and marine waters.
Oxygen makes sense as a series, not a single reading
Oxygen depletion develops over time. In LimnoLog you record oxygen and temperature on every field visit (also offline), see the daily and seasonal trend, and out-of-range values are highlighted automatically.
Open the app → Explore LimnoLog features →Read more