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Drag Force Calculator

Find the drag force on an object moving through air or a fluid.

How it is calculated

The engine computes F = ½ × ρ × v² × Cd × A. Use ρ in kg/m³, v in m/s, Cd as the dimensionless drag coefficient and A in m², and the force comes out in newtons. Velocity is squared, so doubling speed quadruples drag, and the sign of the speed does not matter. Frontal area must be above zero. If density is left empty or not positive it falls back to 1.225 kg/m³ (air at sea level), and a missing or non-positive Cd falls back to 0.47 (a sphere).

Worked example

A car with Cd 0.3 and frontal area 2.2 m² at 30 m/s (108 km/h) in air of 1.225 kg/m³. Dynamic pressure: 0.5 × 1.225 × 30² = 551.25 Pa. Multiply by Cd: 551.25 × 0.3 = 165.375. Multiply by area: 165.375 × 2.2 ≈ 363.83 N.

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Common mistakes

  • Entering speed in km/h or mph. The formula needs m/s, so 108 km/h must be typed as 30.
  • Leaving Cd blank and forgetting that the tool then assumes 0.47, which is a sphere and far too high for a streamlined car.
  • Using total surface area instead of frontal (projected) area.
  • Using air density at sea level for high altitude or for water. Water is about 800 times denser than air, so the density must be changed.
  • Expecting drag to scale linearly with speed. It scales with the square.

About this calculator

This calculator computes aerodynamic drag force using the standard drag equation: F = ½ρv²CdA, where ρ is fluid density, v is velocity, Cd is the dimensionless drag coefficient, and A is the frontal (reference) area facing the flow. The drag coefficient captures how streamlined an object's shape is — a sphere might have Cd around 0.47, while a streamlined airfoil can be under 0.05.

Aerospace and automotive engineers use this formula to size wings, estimate fuel efficiency, and predict terminal velocity for skydivers and falling objects. Air at sea level, at about 1.225 kg/m³, is the usual fluid density, and the force comes out in newtons.

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Comments (1)

  • Editorial team

    Everything is in SI units: density in kg/m3, speed in m/s, area in m2, force in newtons. Since speed is squared, going from 50 to 100 km/h roughly quadruples the force, and the power needed to overcome it grows even faster. If you leave the drag coefficient or the air density empty, the tool quietly falls back to 0.47 and 1.225, so fill them in for anything other than a sphere at sea level. Which object are you modelling?

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