Drag Force CalculatorAir resistance · Fd = ½ρv²CdA
Drag force is the air resistance on a moving object: Fd = ½ρv²CdA. Because it scales with the square of speed, going 30% faster costs about 69% more drag and more than twice the power. Enter a speed, drag coefficient and frontal area to get the drag in newtons and the horsepower needed just to push through the air.
Formula verified against NASA Glenn — Beginner’s Guide to Aeronautics · OpenStax — University Physics, Volume 1
By Manzoor Ahmad · Pharmacist & calculator developerReviewed & updated
Vehicle or object
Cd × A (the drag area) is what really matters. Presets use typical values.
Step-by-step working
What is drag force?
Drag force is the resistance a fluid such as air or water exerts on an object moving through it, acting opposite to the motion. It depends on the fluid’s density, the object’s speed, its size and its shape.
Drag sets a car’s fuel consumption at highway speed, a cyclist’s top speed and a falling object’s terminal velocity. Engineers reduce it by streamlining, which lowers the drag coefficient Cd.
Quick answers
How do you calculate air resistance on a car?
Use F = ½ρv²CdA. A car with Cd 0.30 and 2.2 m² frontal area at 100 km/h sees about 312 N of drag. Rolling resistance adds roughly another 100–150 N.
How much power does it take to overcome drag?
Power = drag × speed = ½ρv³CdA. That cube law is why the same car needs 8.7 kW at 100 km/h but 19 kW at 130 km/h. Convert to hp with the horsepower calculator.
What is a good drag coefficient for a car?
Below 0.25 is excellent: modern EVs reach 0.20–0.23. Most saloons sit around 0.28–0.32, and SUVs and pickups 0.35–0.45.
How does drag affect a cyclist?
At 35–40 km/h on flat ground, drag is about 80–90% of a cyclist’s total resistance. Dropping from the hoods into an aero tuck can cut CdA by 20–30%.
Drag equation
This quadratic drag law fits most everyday objects moving through air or water at moderate to high Reynolds numbers.
| Symbol | Meaning | SI unit |
|---|---|---|
| Fd | Drag force | N |
| ρ | Fluid density | kg/m³ |
| v | Speed relative to the fluid | m/s |
| Cd | Drag coefficient (shape factor) | — |
| A | Frontal area | m² |
| P | Power to overcome drag | W |
How to calculate drag force
- Convert speed to m/s and use the speed relative to the air (add a headwind).
- Square the speed and multiply by ½ρ to get the dynamic pressure.
- Multiply by Cd and A, the shape and size of the object.
- For power, multiply the drag force by the speed.
Worked example: a family car at 100 km/h
A car with Cd = 0.30 and a frontal area of 2.2 m² drives at 100 km/h in sea-level air.
Fd = 472.6 × 0.30 × 2.2 = 311.9 N
P = 311.9 × 27.78 = 8.66 kW ≈ 11.6 hp
At 130 km/h the same car faces 527 N of drag and needs 19.0 kW (25.5 hp), more than double the power for 30% more speed.
Drag coefficients of common shapes and vehicles
Typical published values. A lower Cd means a more streamlined shape.
| Object | Cd | Typical frontal area |
|---|---|---|
| Streamlined body (teardrop) | 0.04 | — |
| Modern EV saloon | 0.20–0.25 | 2.2 m² |
| Typical car | 0.28–0.35 | 2.2 m² |
| SUV / pickup | 0.35–0.45 | 2.8–3.2 m² |
| Sphere | 0.47 | πr² |
| Road cyclist (hoods) | 0.8–1.0 | 0.35–0.4 m² |
| Flat plate facing flow | 1.17–1.28 | — |
Common mistakes to avoid
- Forgetting to square the speed. Drag goes as v², and power as v³.
- Using ground speed in wind. Drag depends on airspeed, so a 20 km/h headwind adds 20 km/h.
- Mixing up Cd and CdA. A small car with a worse Cd can still have less drag than a sleek large one.
Manzoor Ahmad
Pharmacist turned Web Developer & Calculator Engineer · 13+ years in web developmentI’m a pharmacist by training who turned into a full-time tech geek, and for 13+ years I’ve designed and coded web tools. My pharmacy degree included physical pharmacy and pharmaceutics — states of matter, heat, flow and reaction kinetics — so the physics behind these tools is familiar ground, not a new hobby.
I’m not a physicist, so I don’t ask you to take my word for it: every formula on this page is traced to an open university textbook or NIST reference data, and the calculator is tested against published worked examples before it goes live. Spot an error? Tell me and it will be fixed and dated on the next update.
Drag Force Calculator: frequently asked questions
Fd = ½ρv²CdA, where ρ is the fluid density, v the speed, Cd the drag coefficient and A the frontal area.
Yes, with the square of speed. Double the speed and drag quadruples, and the power needed rises eightfold.
Newtons (N), like any force. The drag coefficient itself is dimensionless.
Water is about 800 times denser than air, so at the same speed and shape the drag is about 800 times larger.
Drag is a fluid resistance force, partly from skin friction along the surface and partly from pressure differences around the shape. It is not the same as dry sliding friction.
References & sources
- NASA Glenn — Beginner’s Guide to Aeronautics — The Drag Equation
- OpenStax — University Physics, Volume 1 — Ch. 6.4, Drag Force and Terminal Speed
- HyperPhysics, Georgia State University — air friction
Disclaimer: This calculator is an educational tool built on idealised textbook models. It is not a substitute for professional engineering or safety calculations.