Calculator Inputs
Plotly Graph
The line shows theoretical saturation concentration across temperature. The horizontal dashed line marks your measured dissolved oxygen reading.
Formula Used
The calculator estimates oxygen saturation concentration using a temperature and salinity solubility model, then corrects it for local pressure.
| Theoretical concentration | ln(C) = A0 + A1Ts + A2Ts2 + A3Ts3 + A4Ts4 + A5Ts5 + S(B0 + B1Ts + B2Ts2 + B3Ts3) + C0S2 |
|---|---|
| Temperature transform | Ts = ln((298.15 − T) / (273.15 + T)) where T is in °C |
| Pressure correction | Ccorrected = C × ((P − PH2O) / (760 − PH2O)) |
| Percent saturation | % Saturation = (Measured DO / Ccorrected) × 100 |
| Oxygen deficit | Deficit = Ccorrected − Measured DO |
Higher temperature, higher salinity, and lower pressure all reduce the maximum oxygen that water can hold.
How to Use This Calculator
- Enter a sample name so your exported files stay organized.
- Input water temperature and choose Celsius or Fahrenheit.
- Enter the measured dissolved oxygen concentration in mg/L.
- Add salinity in ppt. Use zero for freshwater samples.
- Enter site altitude, or directly type barometric pressure if known.
- Click Calculate Saturation to show results above the form.
- Review percent saturation, theoretical saturation concentration, and oxygen deficit.
- Use the chart and export buttons for reporting or field records.
Example Data Table
| Sample | Temp (°C) | Measured DO (mg/L) | Salinity (ppt) | Pressure (mmHg) | Saturation Conc. (mg/L) | % Saturation | Deficit (mg/L) |
|---|---|---|---|---|---|---|---|
| River Station A | 20.0 | 8.200 | 0.500 | 748.00 | 8.919 | 91.94% | 0.719 |
| Lake Midpoint | 15.0 | 9.400 | 0.200 | 760.00 | 10.071 | 93.33% | 0.671 |
| Estuary Edge | 25.0 | 7.100 | 12.000 | 755.00 | 7.666 | 92.62% | 0.566 |
FAQs
1) What does percent saturation mean?
It compares measured dissolved oxygen against the theoretical maximum at the same temperature, salinity, and pressure. Values near 100% suggest equilibrium, lower values show depletion, and values above 100% indicate supersaturation from algae, aeration, or rapid cooling.
2) Why does warm water hold less oxygen?
As water warms, gas molecules escape more easily from the liquid phase. That reduces oxygen solubility, so the maximum possible dissolved oxygen concentration drops as temperature rises.
3) Why include salinity in the calculation?
Dissolved salts lower oxygen solubility. Estuaries, brackish water, and marine samples can show noticeably lower saturation concentrations than freshwater at the same temperature and pressure.
4) Why do altitude and pressure matter?
Oxygen enters water from the atmosphere. When atmospheric pressure is lower, the driving force for oxygen dissolution is smaller, so the saturation concentration falls.
5) Is dissolved oxygen in mg/L similar to ppm?
For dilute water samples, mg/L and ppm are usually close enough for practical field interpretation. This calculator reports dissolved oxygen directly in mg/L.
6) What dissolved oxygen level is usually acceptable?
Many aquatic systems perform better above 5 mg/L, while stressed conditions often appear below that point. Sensitive species may require higher oxygen, especially in warm water.
7) Can dissolved oxygen saturation exceed 100%?
Yes. Supersaturation can happen during strong photosynthesis, intense aeration, rapid temperature shifts, or turbulence below dams and waterfalls.
8) Does this calculator replace meter calibration?
No. It helps interpret readings, but you should still calibrate instruments correctly, verify probe membranes, and follow your monitoring protocol for reliable field data.