Drag Force and Terminal Velocity Calculator: Drag Equation, Power and Falling Speed
Find the drag on a moving object and the speed at which a falling one stops accelerating.
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How this calculator works
Enter the density of the fluid, the drag coefficient, the frontal area, the speed and the mass.
The calculator gives the drag force 0.5 rho Cd A v squared, the power drag takes, and the terminal velocity, where the weight equals the drag.
It also gives the time and the distance to reach 95 percent of the terminal velocity.
Formulas used
- F_D = \tfrac12\rho C_d A v^2
- P = F_D v
- v_t = \sqrt{\frac{2mg}{\rho C_d A}}
Worked example
With the default numbers in the calculator above:
- Drag force at this speed: 385.88 N
- Power needed to overcome the drag at this speed: 11.58 kW (15.52 horsepower)
- Terminal velocity of the falling object (the weight equals the drag): 42.78 m/s (154.02 km/h)
- Time and distance to reach 95 percent of the terminal velocity: 7.99 s, after falling 217.18 m
- Weight of the object, for comparison: 784.80 N
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
Why does power go as speed cubed?
Drag grows as the square of the speed, and power is force times speed, so it grows as the cube.
What is terminal velocity?
The speed at which the drag equals the weight, so the object stops speeding up.
What is a drag coefficient?
A number for the shape: about 0.47 for a sphere, 1.2 for a flat plate facing the flow, and 0.3 for a car.
Does it include buoyancy?
No. For a dense object in air it is negligible, but it matters in water.
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Got a question about this? Ask an engineering question and get a plain-language answer with references.
Further reading: White, Fluid Mechanics (drag of bodies); Munson, Fundamentals of Fluid Mechanics.
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