Units

Unit mistakes are a core engineering risk. Properties Library uses one internal unit contract and converts only at the boundary to UI, API, and reports.

Internal contract

Fluid state:

• Temperature is stored internally in K.
• Pressure is stored internally in Pa.

Fluid properties:

• Density: kg/m^3
• Dynamic viscosity: Pa*s
• Kinematic viscosity: m^2/s
• Thermal conductivity: W/m/K
• Heat capacity: J/kg/K

Material properties:

• Density: kg/m^3
• Elastic modulus: GPa
• Strength: MPa
• Thermal conductivity: W/m/K
• Specific heat capacity: J/kg/K

Display units

The UI supports Common SI and Imperial output modes where applicable. Input units can differ from output units.

For example, a fluid calculation can accept temperature in Celsius and pressure in atm, then output Common SI or Imperial results.

API unit metadata

API property values include display fields and raw SI metadata. Existing value and unit fields are the display value for compatibility.

Example structure:

{
  "value": 1.225,
  "unit": "kg/m^3",
  "raw": {"value": 1.225, "unit": "kg/m^3", "unit_system": "si"},
  "display": {"value": 1.225, "unit": "kg/m^3", "unit_system": "si"},
  "dimension": "density"
}

Practical checks

• Confirm the selected output unit system before exporting a report.
• Use the internal state fields for audit checks when consuming the API.
• Do not mix display values from different unit systems in one calculation.
• Prefer raw SI values for downstream engineering calculations.