Drag Force Calculator (F = ½ρv²CdA) & Power to Overcome Drag
By Santaji GadepatilinUpdated October 30, 2026
Drag is the resistance a fluid exerts on a moving object, and it grows with the square of speed. This drag force calculator uses the drag equation F = ½ρv²C<sub>d</sub>A to find the force and the power needed to push through air or water — for cars, cyclists, wind loads, sensors in pipes and falling objects.
How to use the drag force calculator
Enter the fluid density, the speed of the object relative to the fluid, its drag coefficient and its frontal area. You get the drag force and the power needed to overcome it at that speed. Clear any field to solve for it instead — for example, enter a measured drag force and clear Cd to find the drag coefficient.
Drag equation
Fd = ½ ρ v² Cd A
P = Fd × v = ½ ρ v³ Cd A
Example
A car with Cd = 0.30 and 2.2 m² frontal area at 100 km/h (27.78 m/s) in sea-level air:
- F = 0.5 × 1.225 × 27.78² × 0.30 × 2.2 = 311.9 N
- P = 311.9 × 27.78 = 8.66 kW just to push the air aside
Drag force on 1 m² of frontal area in sea-level air
| Shape | Cd | 50 km/h | 100 km/h | 150 km/h |
|---|---|---|---|---|
| Flat plate (normal to flow) | 1.28 | 151.2 N | 604.9 N | 1,361.1 N |
| Cube | 1.05 | 124.1 N | 496.2 N | 1,116.5 N |
| Upright cyclist | 0.9 | 106.3 N | 425.3 N | 957.0 N |
| Sphere (subcritical) | 0.47 | 55.5 N | 222.1 N | 499.8 N |
| Typical car | 0.3 | 35.4 N | 141.8 N | 319.0 N |
| Streamlined car | 0.25 | 29.5 N | 118.2 N | 265.8 N |
| Streamlined body | 0.04 | 4.7 N | 18.9 N | 42.5 N |
Drag coefficients are typical values; the real Cd depends on Reynolds number, surface finish and exact shape.
Notes
- Air density falls with altitude and temperature (about 1.0 kg/m³ at 2,000 m), reducing drag.
- At very low Reynolds numbers (dust, fine droplets) use Stokes’ law instead.
- Terminal velocity of a falling object is where drag equals weight: v = √(2 m g ÷ (ρ Cd A)).
Frequently asked questions
What is the drag force formula?
F = ½ ρ v² Cd A — half the fluid density times speed squared times the drag coefficient times the frontal area.
Why does drag power rise with the cube of speed?
Drag force grows with v², and power is force × speed, so power grows with v³. Driving at 130 km/h instead of 100 km/h needs about 2.2 times the power to beat air drag.
What is a typical drag coefficient?
About 0.25–0.35 for modern cars, 0.47 for a sphere, 1.0–1.3 for flat plates and bluff shapes, and 0.04 for a streamlined teardrop.
Which area should I use?
The frontal area projected onto a plane perpendicular to the flow for vehicles and bluff bodies. Wings use plan area, so check which reference area the Cd value was measured with.