Drag magnitude
Opposes motion relative to the fluid.
Fluid mechanics · Fluid dynamics
Drag force calculator
Estimate drag magnitude from fluid density, relative speed, reference area and a drag coefficient you supply. The secondary output is the mechanical power needed to overcome that drag at the same speed.
Created v1.0
By Thibaut Grzelak, Mechanical Analysis Engineer
02
Results
Drag power
Mechanical power F_d v; excludes drivetrain losses.
Relation and numerical substitution
F_d = 0.5 × ρ × v² × C_d × A—
Quasi-steady quadratic drag with a coefficient valid for the specified flow regime, orientation and reference area.
01Formulas and symbols
Formulas used
F_d
F_d = 0.5 × ρ × v² × C_d × AOpposes motion relative to the fluid.P
P = F_d × vMechanical power F_d v; excludes drivetrain losses.02Assumptions and limits
Scope of validity
- Quasi-steady quadratic drag with a coefficient valid for the specified flow regime, orientation and reference area.
03Validation example
Reference numerical case
- ρ = 1.225 kg/m³, v = 30 m/s, Cd = 0.30 and A = 2.2 m² give Fd = 363.825 N and P = 10914.75 W.
04References
Technical references
FAQ
Does doubling speed double drag?
With constant density, Cd and area, drag quadruples and drag power increases eightfold.
Which area should I enter?
The area used to define your coefficient. It may be frontal or another reference area depending on the data source.
05Model and conventions
Estimate drag magnitude from fluid density, relative speed, reference area and a drag coefficient you supply. The secondary output is the mechanical power needed to overcome that drag at the same speed.
06Limits of this model
Cd is not universal: it can depend on Reynolds number, Mach number, roughness and geometry. This tool does not supply or validate Cd and does not model transient aerodynamic forces.
07Common mistakes
Use velocity relative to the fluid, not ground speed in wind. Pair Cd with its original reference area.