Terminal Velocity Calculator
Balance quadratic drag against weight to estimate terminal speed.
Balance weight with quadratic drag
Terminal velocity occurs when downward weight and upward quadratic drag balance, leaving zero acceleration. This calculator solves the balance for speed using mass, gravitational acceleration, fluid density, projected area, and drag coefficient. It is a useful first estimate for falling objects, particles, or test bodies when the flow regime supports the familiar one-half density times speed squared drag model.
The defaults describe an 80 kilogram body with 0.7 square meter projected area, drag coefficient 1, air density 1.225 kilograms per cubic meter, and gravity 9.81 meters per second squared. The estimated terminal speed is 42.7836 meters per second. Increasing area, density, or drag coefficient lowers that speed; increasing mass raises it under this model.
Treat drag inputs as condition-specific
Drag coefficient is not universal: it changes with shape, orientation, surface, and Reynolds number. Air density varies with altitude and weather, while a tumbling object can change projected area continuously. The calculation also neglects buoyancy unless its effect has already been accounted for. Inputs are processed in your browser, making the estimate private, but experimental or simulation data should guide safety-critical work.
Frequently Asked Questions
What drag model does this use?
It uses quadratic drag equal to one-half fluid density times drag coefficient, area, and speed squared.
Why does projected area matter?
A larger area intercepts more fluid and creates more drag, reducing the balanced terminal speed.
Is drag coefficient constant?
Not always. It can change with shape, orientation, surface condition, and Reynolds number.
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