Drag Force Calculator
Aerodynamic drag is the resistive force a fluid exerts on a body moving through it, and it grows with the square of speed. The drag equation expresses this force as one half of the fluid density times speed squared times the drag coefficient times the frontal area. This calculator takes those four inputs in SI units and returns the drag force in newtons, plus the dynamic pressure and the power needed to overcome drag at that speed, so you can compare designs and conditions.
Drag equation
Drag force F = 0.5 * rho * v^2 * Cd * A
Dynamic pressure q = 0.5 * rho * v^2
Power to overcome drag = F * v
Drag force in kg-force = F / 9.80665
The squared speed term dominates: at twice the speed, drag is four times as large. Dynamic pressure is the drag equation without the shape and area terms. Power is force times speed, the rate of energy needed just to push through the air.
Aerodynamic drag context
- Standard sea-level air density at 15 degrees Celsius is about 1.225 kg/m^3 (International Standard Atmosphere).
- The drag coefficient is dimensionless and set by shape; a sphere is about 0.47, a flat plate near 1.2.
- Drag rises with the square of speed, so power to overcome it rises with the cube.
- To convert mph to m/s multiply by 0.44704; for km/h divide by 3.6.
- One newton equals the force to accelerate one kilogram at one metre per second squared.
Drag force: frequently asked questions
What is the drag equation?
The drag force on a body moving through a fluid is F = 0.5 * rho * v^2 * Cd * A, where rho is fluid density, v is speed, Cd is the drag coefficient and A is the reference (frontal) area. It is a standard relationship in fluid dynamics. The squared speed term means drag rises sharply as you go faster.
Why does drag grow with the square of speed?
Doubling speed doubles both the mass of air struck per second and the velocity given to it, so the rate of momentum transfer, and thus force, rises with the square of speed. Going from 30 to 60 mph roughly quadruples drag, which is why high-speed travel costs so much more energy.
What is a typical drag coefficient?
The drag coefficient is dimensionless and depends on shape. A streamlined car may be around 0.3, a sphere about 0.47, and a flat plate near 1.2. Use a value from a wind-tunnel result or specification for your object; this calculator takes Cd as your input so the result matches your case.
What air density should I use?
The density of dry air at sea level and 15 degrees Celsius is about 1.225 kilograms per cubic metre, a value defined in the International Standard Atmosphere. Density falls with altitude and rises in cold air, so adjust the input if your conditions differ from sea-level standard.
What units does the calculator use?
Enter density in kilograms per cubic metre, speed in metres per second, the drag coefficient as a dimensionless number, and frontal area in square metres. The result is the drag force in newtons. To convert mph to m/s, multiply by 0.44704; to convert km/h, divide by 3.6.
Official sources
- NASA Glenn Research Center: The Drag Equation.
- National Institute of Standards and Technology: SI Units (newton, pascal, watt).
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.