Physics

Instant, private, and free

Drag Equation Calculator.

Calculate quadratic drag force from density, drag coefficient, area, and speed.

On-device calculationNo signup
01

Set your values

Results update as you type.

Drag force: 115.15 N

Drag force

0.000000N
Dynamic pressure: 245 Pa

Dynamic pressure

0.000000Pa

Results update automatically as you type.

Use Cases

Estimate vehicle aerodynamic drag

Input air density, your car's drag coefficient, frontal area, and speed to estimate the aerodynamic drag force acting on the vehicle.

Example: A car with Cd=0.3, area=2.2 m², at 30 m/s in air (density 1.225 kg/m³) experiences about 363 N of drag.

Physics homework and experiments

Use the calculator to quickly compute drag force for lab experiments or to verify theoretical calculations in fluid mechanics.

Example: Calculate drag on a sphere of known diameter and speed in water.

Frequently Asked Questions

What is the drag equation used for?
The drag equation calculates the force of air or fluid resistance on an object moving through a fluid. It's commonly used in physics and engineering to estimate drag on vehicles, projectiles, and other objects.
What units should I use for the inputs?
Use kg/m³ for fluid density, m² for reference area, and m/s for speed. The drag coefficient is dimensionless. The calculator will output the drag force in newtons (N).
What is a typical drag coefficient value?
Drag coefficients vary by shape: a sphere is about 0.47, a streamlined body like an airplane wing is around 0.04, and a flat plate perpendicular to flow is about 1.28. Use known values for your specific object.

Tips & Common Mistakes

Tips

  • Ensure the drag coefficient matches the orientation and shape of your object; it changes with angle of attack.
  • For high speeds, consider that air density decreases with altitude; use the appropriate density for your conditions.
  • The drag force scales with the square of speed, so doubling speed quadruples drag.
  • Use consistent units: kg/m³, m², and m/s to get force in newtons.

Common Mistakes to Avoid

  • Using the wrong reference area: it should be the frontal area (projected area) perpendicular to flow, not total surface area.
  • Forgetting that the drag coefficient is dimensionless and depends on the shape and flow regime; using a value for a different shape.
  • Mixing units, such as using km/h for speed instead of m/s, which leads to incorrect results.

Last updated: August 13, 2026