Drag Force Calculator

How it works

1. 1Enter the fluid density ρ (air at sea level is 1.225 kg/m³), the velocity, the drag coefficient C_d, and the cross-sectional area A.
2. 2The calculator converts velocity and area to SI units, then applies the drag equation F_d = ½·ρ·v²·C_d·A.
3. 3The result is shown in newtons (or lbf). Because drag scales with v², doubling the speed quadruples the drag force.

Use cases

• Estimate aerodynamic drag on a car, cyclist, or runner at a given speed.
• Calculate water resistance on a boat hull or submarine to size propulsion.
• Determine wind load on a building facade or sign for structural checks.

Frequently asked questions

What is the drag force formula?

F_d = ½·ρ·v²·C_d·A, where ρ is fluid density (kg/m³), v is velocity (m/s), C_d is the drag coefficient, and A is the reference area (m²). A 0.2 m sphere (C_d ≈ 0.47, A ≈ 0.0314 m²) at 20 m/s in air (ρ = 1.225) gives F_d ≈ 3.6 N.

What are typical drag coefficient values?

A sphere ≈ 0.47, a streamlined teardrop ≈ 0.04, a passenger car ≈ 0.25–0.35, an upright cyclist ≈ 0.9, and a flat plate facing the flow ≈ 1.17. Lower C_d means less resistance and better aerodynamic efficiency.

What fluid density should I use?

Dry air at sea level and 15°C is 1.225 kg/m³ (the default). Air thins with altitude. Fresh water is ≈ 1000 kg/m³ and sea water ≈ 1025 kg/m³. Use the actual density of the fluid the object moves through.