What equation is used to calculate DO saturation?

This calculator uses the Benson-Krause equation (also called the Garcia-Gordon form), which expresses DO saturation as a function of temperature in Kelvin. It is the basis for Standard Methods for the Examination of Water and Wastewater (APHA) and USGS protocols.

How does temperature affect dissolved oxygen?

Warmer water holds less dissolved oxygen. At 0°C, freshwater saturates at about 14.6 mg/L; at 30°C, only about 7.6 mg/L. This is why summer fish kills occur in warm, shallow ponds.

Why does salinity reduce dissolved oxygen?

Salt ions compete with oxygen molecules for space in solution (salting-out effect) and reduce the partial pressure of oxygen at the water surface. Seawater (~35 ppt) holds roughly 20% less oxygen than freshwater at the same temperature.

How does altitude affect dissolved oxygen saturation?

At higher elevations, atmospheric pressure is lower, so less oxygen can dissolve at equilibrium. At 2,000 m the correction factor is about 0.79, meaning saturation is roughly 21% lower than at sea level.

What do the water quality categories mean?

Hypoxic: 6 mg/L (healthy aquatic ecosystem).

Is 0 ppt salinity the right setting for rivers and lakes?

Yes. Freshwater bodies typically have salinity < 0.5 ppt, so the default of 0 ppt is appropriate. For brackish estuaries use 1–25 ppt; for typical seawater use 35 ppt.

Dissolved Oxygen Saturation Calculator

Name: Dissolved Oxygen Saturation Calculator
Availability: InStock
Author: Nham Vu

Calculate dissolved oxygen (DO) saturation in water at any temperature, salinity, and altitude using the Benson-Krause equation.

Inputs

Water Temperature

Salinity

Freshwater = 0, seawater ≈ 35 ppt

Altitude (optional)

Measured DO (optional)

mg/L

Enter to calculate % saturation and water quality category.

Results

Enter values and click Calculate.

DO Saturation Reference Table

Freshwater, sea level (0 ppt, 1 atm) — Benson-Krause equation

Temp (°C)	Temp (°F)	DO sat (mg/L)

Summary

Calculate dissolved oxygen (DO) saturation in water at any temperature, salinity, and altitude using the Benson-Krause equation.

How it works

Temperature converts from °C or °F to Kelvin (T = °C + 273.15).
DO saturation at standard pressure is calculated with the Benson-Krause equation using Kelvin temperature.
Salinity correction multiplies the result by exp(S × polynomial in 1/T).
Altitude correction multiplies by the pressure ratio P/P₀ where P = 101.325 × exp(−alt/8500) kPa.
If a measured DO value is provided, percent saturation = (measured DO / DO_sat) × 100.

Use cases

Assess oxygen levels in streams, ponds, and reservoirs for aquatic life viability.
Calibrate DO probes by comparing measured readings to theoretical saturation values.
Design aeration systems for wastewater treatment at specific site elevations.
Evaluate hypoxic or eutrophic conditions in water bodies for environmental permits.
Predict seasonal DO swings in fish hatcheries and aquaculture systems.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu