How is dissolved oxygen percent saturation calculated?

Percent saturation equals measured dissolved oxygen divided by the calculated equilibrium solubility, multiplied by 100. Temperature, salinity, and barometric pressure affect the equilibrium value.

Can I convert DO percent saturation to mg/L?

Yes. Select % saturation for the reading unit. The calculator multiplies that percentage by the calculated equilibrium dissolved oxygen concentration.

Should I enter altitude or barometric pressure?

Use measured station pressure when available because weather changes pressure. Altitude mode uses a standard-atmosphere estimate and is therefore approximate.

What ranges does this calculator support?

The modeled range follows USGS DOTABLES: 0–40°C, salinity 0–40‰, and pressure 0.5–1.1 atm. Altitude is limited to values that produce pressure within that range.

Does a calculated DO value prove that water quality is safe?

No. This is an equilibrium and unit-conversion calculator, not a regulatory or ecological verdict. Applicable thresholds depend on species, jurisdiction, sampling method, and other conditions.

Is salinity in g/L the same as parts per thousand?

Not exactly. This calculator accepts salinity in per mille (approximately grams per kilogram), matching the model input. It does not silently treat grams per liter as equivalent.

Dissolved Oxygen Saturation Calculator

Calculate equilibrium dissolved oxygen in mg/L or convert a measured DO value between mg/L and percent saturation using temperature, salinity, and pressure.

Water and reading inputs

Water temperature

Supported range: 0–40°C (32–104°F).

Salinity

‰ (ppt)

0 = freshwater; typical seawater is about 35‰.

Altitude or barometric pressure

Altitude estimates pressure. Use measured station pressure when available.

Measured DO (optional)

Results

Enter valid values and select Calculate.

Freshwater saturation reference

0‰ salinity and 760 mmHg pressure, calculated with the same model.

°C	°F	DO (mg/L)

Method and sources

The calculation follows the Benson-Krause oxygen-solubility approach used by USGS DOTABLES. Pressure correction accounts for water-vapor pressure; altitude mode uses a standard-atmosphere estimate.

Summary

Calculate equilibrium dissolved oxygen in mg/L or convert a measured DO value between mg/L and percent saturation using temperature, salinity, and pressure.

How it works

Temperature is converted to Celsius and Kelvin. The supported model range is 0–40°C.
The Benson-Krause freshwater equation estimates oxygen solubility at standard atmospheric pressure.
A salinity correction is applied for 0–40‰ salinity.
Measured pressure is normalized to 760 mmHg; altitude mode estimates pressure from the standard atmosphere.
A measured mg/L value is divided by equilibrium solubility to obtain percent saturation. A percent value is multiplied by equilibrium solubility to obtain mg/L.

Use cases

Convert a dissolved-oxygen probe reading from mg/L to percent saturation.
Convert a percent-saturation reading to estimated dissolved oxygen in mg/L.
Estimate the expected saturation concentration before calibrating a field probe.
Compare temperature and salinity scenarios using a consistent equilibrium model.
Account for measured station pressure instead of relying only on elevation.

Frequently Asked Questions

Last updated: 2026-09-20 · Reviewed by Nham Vu