The density ρ of the Rolls-Royce RB.181 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)