Assess aquatic health with oxygen saturation estimates. Adjust for temperature, salinity, and site pressure effects. Export reports to support field sampling and compliance checks.
The calculator estimates the dissolved oxygen saturation concentration using a temperature–salinity solubility relationship and then applies a local-pressure correction. The core solubility model is the Weiss formulation for oxygen in seawater, evaluated at the selected temperature T (K) and salinity S (ppt/PSU):
Local saturation is approximated by scaling for the dry-air pressure ratio (P − Pv) and oxygen fraction (default 0.2095), where P is atmospheric pressure and Pv is water vapor pressure at the water temperature.
| Temperature (°C) | Salinity (ppt) | Pressure (kPa) | Measured DO (mg/L) | DO Saturation (mg/L) | Percent Saturation (%) |
|---|---|---|---|---|---|
| 20 | 0 | 101.325 | 7.5 | ≈ 9.1 | ≈ 82 |
| 10 | 0 | 101.325 | 10.0 | ≈ 11.3 | ≈ 88 |
| 25 | 35 | 101.325 | 6.0 | ≈ 7.0 | ≈ 86 |
| 15 | 0 | 85 | 7.0 | ≈ 8.2 | ≈ 85 |
Dissolved oxygen (DO) saturation compares the oxygen present in water to the maximum it can hold under the same conditions. A reading of 100% means the water is in equilibrium with the atmosphere, while values below 100% indicate oxygen demand from biology or chemistry. In fisheries and hatcheries, sustained low saturation can reduce feeding, growth, and survival.
Cold water holds more oxygen than warm water. For example, near sea level and freshwater conditions, saturation can be about 11.3 mg/L around 10 °C, but closer to 8.3 mg/L around 25 °C. This calculator models the temperature effect first, then applies corrections for salinity and pressure.
As salinity rises, oxygen solubility drops because dissolved salts change water’s ability to dissolve gases. In coastal waters near 35 PSU, saturation concentrations are typically lower than freshwater at the same temperature. This is why estuaries can show lower mg/L at the same percent saturation compared with rivers.
Oxygen saturation increases with higher barometric pressure and decreases at altitude. A lake at 1,500 m often experiences noticeably lower saturation mg/L than sea level even on the same day. This calculator lets you use either direct pressure (kPa, atm, mmHg) or altitude-based estimates for a practical field workflow.
Percent saturation is computed as: %Sat = (Measured DO / DOsat) × 100. If your measured DO is 8.0 mg/L and the modeled saturation is 10.0 mg/L, the water is at about 80% saturation. This format is helpful when comparing sites with different temperatures and elevations.
Many healthy streams operate near 90–110% saturation, with short spikes above 100% possible during strong photosynthesis. Persistent values below ~60–70% can stress sensitive species, especially at higher temperatures. Always interpret results with site context, time of day, and flow conditions.
Calibrate DO probes regularly, confirm temperature compensation, and avoid air bubbles in sample bottles. In slow-moving or stratified waters, measure multiple depths because surface oxygen can differ from bottom layers. Recording barometric pressure improves accuracy when comparing across days and weather changes.
Percent saturation supports standardized reporting across seasons. Pair DO saturation with biochemical oxygen demand (BOD), nutrient data, and turbidity to diagnose drivers of low oxygen. Exporting CSV or PDF from this page helps document inputs, modeled saturation, and calculated percent saturation for audits and lab notebooks.
It means the water’s DO equals the modeled equilibrium maximum for the same temperature, salinity, and pressure. It does not mean “high oxygen” in absolute mg/L; warm water can be 100% at a lower mg/L than cold water.
Yes. Photosynthesis, rapid aeration, or turbulent mixing can temporarily push DO above equilibrium, creating supersaturation. Short periods can be normal, but extreme supersaturation may stress aquatic organisms.
Salt lowers oxygen solubility. Without salinity correction, saturation mg/L may be overestimated, making the calculated percent saturation appear lower than it truly is for seawater and estuaries.
Use measured barometric pressure when available for best accuracy. If you only know elevation, altitude mode provides a reasonable estimate. Weather changes can shift pressure, so measured values improve day-to-day comparisons.
Enter DO in mg/L, which is the most common unit for field probes and lab reports. If your instrument reports ppm, it is typically equivalent to mg/L for dilute freshwater conditions.
It is suitable for education and field estimation and includes temperature, salinity, and pressure effects. For regulatory reporting, follow your agency’s approved method and verify with calibrated instruments and documented procedures.
Because saturation depends on temperature and pressure. Cooler temperatures or higher pressure increase the saturation limit, reducing percent saturation for the same mg/L. Warm days or lower pressure do the opposite.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.