Analytical · Free Calculator

Dissolved Oxygen Saturation Calculator

Find the oxygen solubility in water at the sample temperature, salinity and pressure, and convert a measured DO in mg/L to percent saturation.

DO saturationTemperatureSalinity% saturation

Water temperature

°C

Salinity

g/kg (‰)

Barometric pressure

mbar

Measured DO

mg/L

DO at saturation9.09 mg/L

Measured saturation82.5 %

At 1013 mbar9.09 mg/L

How this result was calculated

ln C* = −139.34411 + 1.575701 × 10⁵/T − 6.642308 × 10⁷/T² + 1.2438 × 10¹⁰/T³ − 8.621949 × 10¹¹/T⁴ − salinity term
C* = 9.092 mg/L at 1 atm; × P ÷ 1013.25 = 9.09 mg/L

Oxygen Solubility (Benson and Krause)

ln C* = −139.34411 + 1.575701×10⁵/T − 6.642308×10⁷/T² + 1.243800×10¹⁰/T³ − 8.621949×10¹¹/T⁴ − S(1.7674×10⁻² − 10.754/T + 2140.7/T²)

T in kelvin, S salinity in g/kg; C* in mg/L at 1 atm, as used in Standard Methods for dissolved oxygen (4500 O). The pressure correction here is a simple proportion, which is accurate to within about 1 % near normal pressures.

Worked example

Fresh water at 20 °C and 1013 mbar holds 9.09 mg/L at saturation, so a reading of 7.5 mg/L is 82.5 % saturation.

Key insight: warm water holds much less oxygen: about 14.6 mg/L at 0 °C but only 7.6 mg/L at 30 °C. Aeration control in treatment plants must account for this seasonal change.