Dissolved Oxygen Saturation Calculator
Percent saturation needs the saturation value first. Enter water temperature and elevation to get DO saturation in mg/L — the denominator for every percent-saturation calculation.
DO Saturation
| Item | Value |
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How the calculation works
Formulas (APHA 4500-O, freshwater)
T (kelvin) = °C + 273.15 (°C = (°F − 32) × 5/9)
ln Cs = −139.34411 + 1.575701×105/T − 6.642308×107/T² + 1.243800×1010/T³ − 8.621949×1011/T4
Cs (mg/L) = eln Cs, at 1 atm
P/P0 = (1 − 2.25577×10−5 × h)5.25588 (h in meters)
Cs at elevation = Cs (sea level) × P/P0
T (kelvin) = °C + 273.15 (°C = (°F − 32) × 5/9)
ln Cs = −139.34411 + 1.575701×105/T − 6.642308×107/T² + 1.243800×1010/T³ − 8.621949×1011/T4
Cs (mg/L) = eln Cs, at 1 atm
P/P0 = (1 − 2.25577×10−5 × h)5.25588 (h in meters)
Cs at elevation = Cs (sea level) × P/P0
Notes & limitations
The saturation polynomial is the APHA Standard Methods (4500-O) equation for oxygen solubility in freshwater (Benson & Krause), valid from 0 to 40 °C. The elevation correction scales saturation by the barometric pressure ratio from the standard atmosphere.
- Fresh water only. Dissolved salts lower oxygen solubility — seawater holds roughly 80% of the freshwater value at the same temperature. Use the Weiss equation for brackish or marine water.
- Percent saturation = measured DO ÷ saturation DO × 100. Use this tool’s result as the denominator.
- Equation range is 0–40 °C; values outside that range are not computed here.
- Use the saturation value to check DO probe calibration: a probe reading well above saturation in clean water usually needs service, not a new membrane.