The density ρ of the Rolls-Royce Allison Model 250 engine or any substance in aircraft design is defined as the mass of the substance per unit volume. It is commonly measured in kilograms per cubic meter (kg/m³) in the International System of Units (SI).
- Ρ = Density of the fluid (in kilograms per cubic meter, kg/m³)
- P = Pressure of the fluid (in pascals, Pa)
- R = Specific gas constant for the fluid (in J/(kg·K))
- T = Temperature of the fluid (in kelvin, K)