Arrasto (força)
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
F = ½ρv²CdA
About this calculator
The aerodynamic drag calculator determines the resistance force a fluid exerts on a moving object. It uses the formula F = ½ρv²Cd·A, where ρ is fluid density, v is relative velocity, Cd is drag coefficient, and A is reference area. This tool is useful for engineers, designers, and enthusiasts who need to estimate drag on vehicles, aircraft, or structures exposed to wind.
The calculation is based on the classic drag equation, which considers air (or other fluid) density, velocity squared (making drag very sensitive to speed), a coefficient dependent on shape and surface roughness, and the frontal projected area. The result is given in newtons (N), making it easy to compare with other forces involved in motion.
You can use this calculator in many practical situations: to estimate extra fuel consumption of a car due to aerodynamic drag, to size brake systems for high-speed vehicles, or to evaluate stability of structures like bridges and buildings under strong winds. It is also useful in bike, parachute, and amateur rocket designs.
Important caveats: drag coefficient (Cd) varies greatly with shape and flow regime (laminar or turbulent). Typical values range from 0.04 for a streamlined airfoil to over 1.0 for a blunt body. Make sure to use a Cd appropriate for your object. Also, the formula assumes incompressible fluid and uniform flow, which is not valid for supersonic speeds or highly viscous fluids.
Frequently asked questions
What is the drag coefficient (Cd) and how do I find it?
Cd is a dimensionless number representing aerodynamic resistance. You can find tabulated values in engineering books or specialized websites. For a sphere, Cd ≈ 0.47; for a typical car, Cd ≈ 0.3.
Does the calculator work for liquids like water?
Yes, as long as the density (ρ) is adjusted for the fluid. For water, ρ ≈ 1000 kg/m³. The formula is the same, but drag in liquids is much higher due to increased density.
What unit should I use for velocity?
Use meters per second (m/s) to get the result in newtons. If you use km/h, convert by dividing by 3.6. The calculator may accept different units, but the standard is SI.
What is the reference area (A) in the formula?
It is the frontal projected area of the object, i.e., the area of its shadow when viewed from the front. For a car, it is the front area. For a sphere, it is the area of the great circle (πr²).
Can I use this calculator for supersonic speeds?
No, the formula assumes incompressible fluid, which is not valid above Mach 0.3. For supersonic speeds, compressibility effects significantly alter drag.