Drag Force Calculator
Calculate aerodynamic or fluid drag force using F_D = ½ρv²CdA. Covers high-Reynolds standard drag, Stokes creeping flow, vehicle drag comparison, and power required to overcome drag.
kg/m³
m/s
m²
Drag Force F_D
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Drag Force —
Dynamic Pressure q —
Extended More scenarios, charts & detailed breakdown ▾
kg/m³
m/s
m²
Drag Force (N)
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Power to Overcome Drag —
Professional Full parameters & maximum detail ▾
kg/m³
m/s
m²
kg
Drag Force
Drag Force F_D —
Dynamic Pressure q —
Power & Load
Power to Overcome Drag —
Power (kW) —
Drag/Weight Ratio —
Aerodynamic Note
Drag Crisis Note (sphere) —
How to Use This Calculator
- Select or enter the drag coefficient Cd for your object.
- Enter fluid density (air at sea level = 1.225 kg/m³).
- Enter velocity in m/s and reference area in m².
- Results show drag force and dynamic pressure. Use Extended tabs for Stokes drag or vehicle comparison.
Formula
F_D = ½ × ρ × v² × Cd × A
ρ = fluid density (kg/m³) | v = velocity (m/s) | Cd = drag coefficient | A = reference area (m²)
Stokes (low Re): F = 6πμrv
Example
Example: Car, Cd=0.30, ρ=1.225, v=30 m/s (108 km/h), A=2.2 m² → F_D = 0.5×1.225×900×0.30×2.2 = 363 N. Power = 363×30 = 10.9 kW.
Frequently Asked Questions
- The drag force is F_D = ½ × ρ × v² × Cd × A, where ρ is fluid density (kg/m³), v is velocity (m/s), Cd is the drag coefficient (dimensionless), and A is the reference area (m²). This applies to high Reynolds number flows.
- Sphere: 0.47, half-sphere: 0.42, cylinder (side-on): 1.05, flat plate normal to flow: 1.28, streamlined body: 0.04, modern car: 0.25–0.35, SUV: 0.35–0.45, semi-truck: 0.6–0.9, cyclist: 0.88–1.0.
- At Re ≈ 3 × 10⁵ for a smooth sphere, the boundary layer transitions from laminar to turbulent, allowing it to stay attached further and reducing Cd from ~0.47 to ~0.20. Golf ball dimples artificially trigger this transition at lower Re.
- For very small objects at low Reynolds number (Re << 1), viscous forces dominate and the drag is F = 6πμrv (Stokes law). This applies to particles settling in fluid, aerosols, and microorganisms.
- Power = F_drag × velocity. Drag power scales as v³. A car with 300 N drag at 30 m/s needs 9,000 W (9 kW) just to overcome air resistance. At 60 m/s, drag force quadruples and power requirement multiplies by 8.
Related Calculators
Sources & References (5) ▾
- NASA Glenn Research Center – Drag Equation — NASA Glenn Research Center
- OpenStax University Physics Vol. 1 Chapter 6 – Drag Force — OpenStax
- Hoerner S F — Fluid Dynamic Drag, 2nd Ed. — Hoerner Fluid Dynamics
- NACA Technical Reports – Aerodynamic Drag (historical) — NASA Technical Reports Server
- SAE International – Aerodynamics and Fluid Mechanics — SAE International