Density Calculator and Unit Conversion

Use at your own risk. Verify inputs, assumptions and results independently before applying them.

Input definitions

Reference temperature: Temperature at which the reference density is known. Unit: deg C.
Density at reference temperature: Known lubricant density at the reference temperature. Unit: kg/m^3.
Operating temperature: Temperature for which the operating density should be estimated. Unit: deg C.
Density at reference pressure: Lubricant density at the reference pressure before compression. Unit: kg/m^3.
Operating pressure: Pressure at which compressed lubricant density should be estimated. Unit: GPa.
Property: Property family to convert: density, dynamic viscosity, or kinematic viscosity.
From: Factor for the selected source unit relative to the property base unit. Unit: property-dependent.
To: Factor for the selected target unit relative to the property base unit. Unit: property-dependent.
Value: Input value in the selected source unit. Unit: selected source unit.

Worked example

For the temperature relation, enter reference temperature 60 °C, reference density 850 kg/m³ and target temperature 40 °C. The calculator gives 863 kg/m³ using its empirical temperature coefficient. In the pressure relation, reference density 850 kg/m³ and pressure 0.1 GPa give approximately 892 kg/m³. These separate correlations are screening estimates, not a combined equation of state. For a unit-conversion check, 1 g/cm³ equals 1000 kg/m³.

Density Temperature Relation

Density depends on temperature, even though the dependency is relatively small compared to lubricant viscosity. Here is an empirical formula that can be used to calculate the change of density with temperature (Grease Lubrication in Rolling Bearings):

(1) $\begin{eqnarray*} \rho = \rho_{T_1} + \alpha_p (T_1 - T) \\ \end{eqnarray*}$

where $\alpha_p=0.65$ for $831kg/m^3 <\rho<950 kg/m^3$ and $\alpha_p=0.6$ for $950 kg/m^3 <=\rho<1000 kg/m^3$ . As it can be seen, this empirical relation applies only for the oils having the densities in a specified range, however, this range covers most commonly used lubricating oils (860-980 $kg/m^3$ ).

Use the temperature relation tab in the calculator below to calculate density at the given operating temperature.

Density Pressure Relation

When the lubricating oil is compressed, density of the oil increases. This increase starts to be noticeable at relatively high pressures (>0.1GPa), which is however quite common for Elastohydrodynamic conditions (EHL). In EHL, the most widely used formula to describe the change of oil density with pressure is known as Dowson and Higginson density equation:

(2) $\begin{eqnarray*} \rho = \rho_{0} \frac{0.59 \times 10^9 + 1.34p}{0.59 \times 10^9 + p} \\ \end{eqnarray*}$

Use the pressure relation tab to estimate compressed oil density at EHL-relevant pressures.

Density Unit Conversion

The calculator also includes a simple density and viscosity unit conversion tool. Choose the property type, source unit, target unit, and value in the unit conversion tab.