Drag Force Calculator
This drag force calculator finds the aerodynamic or hydrodynamic drag on an object from its speed, frontal area, drag coefficient, and the fluid density, using the drag equation. Enter the values and the drag force calculator returns the drag force in newtons. It works for cars, cyclists, balls, and anything moving through air or water.
Results
The Drag Force Calculator is part of our Motion & Force collection. Browse more motion & force to size, convert, and check your work alongside this tool.
What the drag force calculator shows
Moving through air or water means pushing fluid out of the way, and that costs force. The drag force calculator gives that resisting force from the drag equation. Because drag grows with the square of speed, it becomes the main force a fast car or cyclist has to overcome.
Drag force calculator formula
The drag force calculator uses the drag equation:
ρ is the fluid density, v the speed, Cd the drag coefficient, and A the frontal area. Doubling the speed quadruples the drag, and the power needed to overcome it grows with the cube of speed.
Aerodynamic drag calculator example
An object of 1 m² frontal area and drag coefficient 0.5 moving at 20 m/s (72 km/h) in air. The aerodynamic drag calculator gives:
At 40 m/s the drag rises to 490 N, four times as much.
How to use the drag force calculator
Enter the speed in metres per second, the frontal area in square metres, the drag coefficient, and the fluid density. Use 1.225 kg/m³ for air at sea level and about 1,000 kg/m³ for water. The drag force calculator returns the drag in newtons. Typical drag coefficients are listed in the table below.
Reading the drag force calculator result
The drag force is what an engine, motor, or rider must push against to hold that speed. Multiply drag by speed to get the power: 122.5 N at 20 m/s is about 2.45 kW. The drag coefficient is the hardest input to know; streamlining lowers it far more than shrinking the frontal area usually can.
When to use the drag force calculator
- Estimating car or bike resistance with the drag force calculator
- Comparing shapes by drag coefficient
- Finding terminal speed of a falling object
- Physics problems on air resistance
Common drag force calculator mistakes
- Speed in km/h. Convert to m/s by dividing by 3.6.
- Using side area. Use the frontal area facing the flow.
- Wrong density. Air and water differ by about 800 times.
Tips for accurate results
- Use a measured Cd for your exact shape when you can.
- Lower the air density at high altitude.
- Multiply drag by speed for the power required.
Drag coefficient calculator: finding Cd
A drag coefficient calculator works the equation backwards: Cd = 2Fd ÷ (ρ v² A). Measure the drag force in a wind tunnel or coast-down test at a known speed, and the coefficient follows. Cd depends on shape and surface, and changes somewhat with speed. To convert a speed reading into metres per second, the velocity calculator handles distance and time.
Terminal velocity from the drag force calculator
A falling object speeds up until drag equals its weight. Setting ½ρv²CdA = mg and solving for v gives terminal velocity. A skydiver lying flat reaches about 55 m/s; curled up, with less area, the terminal speed is higher.
Drag coefficient calculator reference values
| Shape | Drag coefficient Cd |
|---|---|
| Streamlined body | 0.04 |
| Modern car | 0.25 to 0.35 |
| Sphere | 0.47 |
| Cyclist upright | 0.9 |
| Flat plate (face-on) | 1.28 |
Drag Force Calculator FAQ
What is the drag equation?
Fd = ½ ρ v² Cd A: half the fluid density times speed squared times the drag coefficient times the frontal area.
How do I find the drag coefficient?
Rearrange the drag equation: Cd = 2Fd ÷ (ρ v² A), using a measured drag force, or use published values for similar shapes.
Why does drag rise so fast with speed?
Drag depends on speed squared, so doubling speed gives four times the drag.
Does drag apply in water too?
Yes. Use water density, about 1,000 kg/m³, which makes drag far larger than in air.