Drag Coefficient Calculator
Calculate aerodynamic drag force on objects moving through air or fluid.
Enter velocity, area, and drag coefficient (Cd) to find drag force in Newtons and pounds-force.
Drag force is the resistance force exerted by a fluid (air, water) on a moving object. Understanding drag is fundamental in automotive engineering, aviation, sports science, and ballistics. Every vehicle, aircraft, and projectile must overcome drag to maintain or increase speed.
The Drag Force Equation
F_D = ½ × ρ × v² × A × C_D
Where:
- F_D = Drag force (Newtons)
- ρ (rho) = Fluid density (kg/m³) — air at sea level ≈ 1.225 kg/m³
- v = Velocity of the object relative to the fluid (m/s)
- A = Reference area (frontal area of the object, m²)
- C_D = Drag coefficient (dimensionless — depends on shape)
The Role of Velocity
Drag force increases with the square of velocity. Doubling speed quadruples drag. This is why fuel consumption increases sharply at highway speeds — the engine must overcome four times more air resistance at 120 km/h than at 60 km/h.
Typical Drag Coefficients (C_D)
| Object | Typical C_D |
|---|---|
| Sphere | 0.47 |
| Bicycle + rider | 0.88 |
| Sedan car (efficient) | 0.25–0.30 |
| SUV / minivan | 0.35–0.45 |
| Semi-truck | 0.65–0.80 |
| Skydiver (belly-to-earth) | 1.0 |
| Commercial aircraft | 0.02–0.05 |
| Human walking | 1.0–1.3 |
| Airfoil (efficient) | 0.04 |
Air Density
Air density varies with altitude and temperature:
- Sea level, 15°C: 1.225 kg/m³
- 1,000 m altitude: 1.112 kg/m³
- 2,000 m altitude: 1.007 kg/m³
- 5,000 m altitude: 0.736 kg/m³
Practical Example
A car with C_D = 0.28, frontal area = 2.3 m², traveling at 120 km/h (33.33 m/s) in standard air (1.225 kg/m³): F_D = ½ × 1.225 × (33.33)² × 2.3 × 0.28 F_D = ½ × 1.225 × 1111 × 2.3 × 0.28 = 438 Newtons (98.5 lbf)