Freshwater Density From Temperature

Evaluate the standard empirical pure-freshwater density approximation near atmospheric pressure for 0–40°C; excludes salinity, compression and dissolved-solids effects.

Description

Pure freshwater density varies nonlinearly with temperature and peaks close to 4°C.

Pure freshwater density varies nonlinearly with temperature and peaks close to 4°C. An empirical near-atmospheric-pressure approximation captures that pattern over its stated range.^[1]

The tool returns freshwaterDensitiesKgPerM3. The computation uses supplied observations and parameters rather than acquiring measurements.

When to use Freshwater Density From Temperature

Use this for the following task: Evaluate the standard empirical pure-freshwater density approximation near atmospheric pressure for 0–40°C; excludes salinity, compression and dissolved-solids effects. Prepare observations and calibration parameters on the same unit and reporting basis.

How to use Freshwater Density From Temperature and understand its results

Prepare the measured quantities and supplied model parameters. Match the units and align paired lists before calculating.
Enter temperaturesC according to the field table, then run the tool.
Read freshwaterDensitiesKgPerM3. Use the calculation below to interpret the selected mean or the model’s signs, units and comparison flags.
Review the supplied assumptions and calibration before comparing or reporting the result.

Input field	Meaning	Value type and bounds	Requirement
temperaturesC	Temperatures c	list of number	Required

Supply a nonempty temperature list from 0 through 40°C. Evaluate the approximation for each entry and return kg/m³ in original order.

density=1000×[1−((T+288.9414)/(508929.2×(T+68.12963)))×(T−3.9863)²]

The symbols and boundary conditions refer to the supplied fields and the implementation described above.

Output field	Meaning	Value type
freshwaterDensitiesKgPerM3	Freshwater densities kg per m3	list of number

json

{
  "input": {
    "temperaturesC": [
      0,
      4
    ]
  },
  "output": {
    "freshwaterDensitiesKgPerM3": [
      999.8675791619049,
      999.9999985022105
    ]
  }
}

Limitations and assumptions

This excludes salinity, dissolved solids and compression effects. Temperatures outside the empirical range are rejected rather than extrapolated.

Numerical inputs must be finite. Input-shape and calculation checks do not establish measurement quality or the validity of a supplied calibration.

Alternative or Complementary methods

Choose Density Gradient Stratification Strength when you need its operation: Compute signed N² from observed density gradients with depth positive down; negative values remain instability indicators rather than an invented real Brunt–Väisälä frequency. Choose Fall Turnover Density Inversion Trigger for the complementary operation: Screen resolved down-column density inversions against caller measurement tolerance; inversion is a mixing trigger screen, not proof of complete fall turnover.

Background reference: Lakes and Reservoirs: Guidelines for Study Design and Sampling.

References

Lakes and Reservoirs: Guidelines for Study Design and Sampling — U.S. Geological Survey

Similar or alternative tools

Density Gradient Stratification Strength
Compute signed N² from observed density gradients with depth positive down; negative values remain instability indicators rather than an invented real Brunt–Väisälä frequency.
Fall Turnover Density Inversion Trigger
Screen resolved down-column density inversions against caller measurement tolerance; inversion is a mixing trigger screen, not proof of complete fall turnover.