How Fast Does Rain Fall? Terminal Velocity and Air Resistance Explained
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The falling speed of a raindrop is surprisingly modest: depending on the drop's size, it reaches only about ten to twenty metres per second. As a drop falls from the clouds under gravity, it first accelerates, but air resistance quickly balances the pull of gravity. From that point onward the drop covers the rest of its journey to the ground by inertia at a constant speed (more on the history of falling bodies: Galileo on the free fall of bodies).
That constant speed is called terminal velocity — the maximum speed a falling object reaches when the drag force from the surrounding air exactly cancels the force of gravity. Terminal velocity is why a raindrop lands harmlessly instead of striking like a bullet, and understanding it explains everything from skydiving to hailstorms.
What is terminal (steady) falling velocity?
Terminal velocity is the highest speed an object attains while falling through a fluid such as air, reached once the resisting drag force equals the object's weight. At this point the net force on the object is zero, so by Newtonian physics the object no longer accelerates and continues at a constant velocity until it lands.
Definition of terminal velocity
Terminal velocity is defined as the constant speed a freely falling object eventually reaches when air friction (or fluid resistance) balances the downward force of gravity. Before this equilibrium, the object is in free fall and gains speed at roughly 9.8 m/s² near the surface of Earth. Once terminal velocity is reached, that acceleration drops to zero. A raindrop settles at 10–20 m/s, while a human body in a spread position levels off near 55–60 m/s.
How force equilibrium is reached during a fall
Force equilibrium during a fall is reached when the upward drag force grows to match the object's weight, because drag increases with speed. At the instant of release, gravity is the only significant force and the object accelerates. As velocity rises, air resistance climbs — for large, fast-moving objects it grows roughly with the square of the speed — until the two forces are equal and opposite. From that moment the object falls at a steady terminal velocity. This is a direct application of Newton's laws: no net force means no acceleration.
Air resistance and the drag force
Air resistance is the force that stops falling objects from accelerating indefinitely, and without it the world would be a dangerous place. If raindrops met no air resistance, their falling speed would reach hundreds of metres per second and they would kill like bullets. Small animals and birds would be wiped out, and people would have to arm themselves with iron umbrellas and wear chain mail and helmets instead of raincoats.
Large, heavy hailstones, however, still fall at high speed. They smash windowpanes, destroy crops, and damage orchards — a reminder that drag scales with size and that a bigger object can push its terminal velocity far higher than a tiny droplet.
Gravity, drag, and buoyancy
Three forces act on any object falling through air: gravity pulling it down, drag opposing its motion, and buoyancy providing a small upward push equal to the weight of displaced air. For dense objects in air, buoyancy is negligible, so terminal velocity is set almost entirely by the balance between gravity and drag. In a dense fluid such as water or oil, buoyancy becomes significant and lowers the settling velocity considerably.
The drag force formula and the drag coefficient
The drag force formula lets you calculate terminal velocity precisely. For turbulent flow, drag equals ½ · ρ · v² · Cd · A, where ρ is air density, v is velocity, Cd is the drag coefficient, and A is the object's cross-sectional area. Setting drag equal to weight (mg) and solving for v gives the terminal velocity:
- v = √(2mg / (ρ · Cd · A))
- m — mass of the object
- g — gravitational acceleration (about 9.8 m/s² on Earth)
- ρ — density of the air
- Cd — drag coefficient, which depends on shape
- A — projected frontal area
The square-root relationship shows why heavier or more compact objects fall faster: doubling the mass raises terminal velocity by only about 41 percent, not double, because velocity depends on the square root of mass.
Creeping flow and Stokes' law
For very small particles falling slowly, drag follows Stokes' law rather than the squared-velocity formula. In this creeping-flow regime — described by physicist George Stokes — the resistance is directly proportional to velocity, radius, and the fluid's viscosity. Stokes' law governs the settling velocity of fine dust, fog droplets, and sediment, and it underpins the falling sphere viscometer, a laboratory instrument that measures a fluid's viscosity by timing how fast a small ball sinks through it. Whether an object obeys Stokes' law or the turbulent drag equation is decided by the Reynolds number, a dimensionless value comparing inertial forces to viscous forces in the flow.
Factors that affect terminal velocity
Terminal velocity is not a single fixed number — it changes with the object's mass, shape, orientation, and the density of the air it falls through. Four variables dominate.
The effect of the object's mass
A heavier object of the same size and shape reaches a higher terminal velocity, because more weight must be balanced before drag catches up. This is why a lead ball settles faster than a foam ball of identical size. Mass enters the terminal velocity formula under a square root, so the effect is real but gradual rather than proportional.
The effect of air density and altitude
Thinner air raises terminal velocity, which is why falls from extreme altitude reach far greater speeds. Because ρ (air density) sits in the denominator of the formula, the low-density air of the upper atmosphere lets a body accelerate to speeds impossible near the ground. Dr. Alan Eustace and Felix Baumgartner both exploited this in their record-breaking jumps from the stratosphere, briefly exceeding the speed of sound before the thickening air slowed them.
The effect of body position during a fall
Body position dramatically changes a skydiver's terminal velocity by altering the frontal area exposed to the air. A flat, spread-eagle (belly-to-earth) position maximises area and drag, giving a terminal velocity around 55 m/s. A head-down, streamlined dive minimises area and can push speeds well past 90 m/s. Skydivers use this control to speed up, slow down, and manoeuvre relative to one another.
The effect of an object's area and shape
A larger surface area and a less streamlined shape both lower terminal velocity by increasing drag. A flat sheet of paper flutters down slowly, while the same sheet crumpled into a ball falls much faster despite identical mass — the change is purely in area and drag coefficient. This is the exact principle a parachute exploits.
Skydiving and the falling speed of a human
A skydiver's terminal velocity in free fall is roughly 55–60 metres per second in a stable belly-down position. During a delayed parachute jump, a skydiver who has leapt from the aircraft falls with increasing acceleration for the first eight to ten seconds. At about the tenth second of the fall, the mounting air resistance completely balances the force of gravity.
If the skydiver does not open the parachute, they will keep falling at a constant speed of roughly sixty metres per second. Hitting the ground at such an enormous velocity would inevitably be fatal — which is why the parachute is essential rather than optional.
How a parachute slows the fall
An open parachute slashes terminal velocity by hugely increasing drag through its wide canopy shape. Once deployed, the umbrella-like canopy meets far greater air resistance and sharply brakes the falling speed, so the skydiver touches down at a safe velocity of only a few metres per second. In the drag formula this works by enlarging both the area A and the drag coefficient Cd, dropping terminal velocity from a lethal 60 m/s to a survivable landing speed.
Comparing the terminal velocities of different objects
Terminal velocity spans a huge range across everyday objects, from a gently drifting raindrop to a diving bird faster than a race car.
- Raindrop: about 10–20 m/s
- Skydiver (belly-down): about 55–60 m/s
- Skydiver (head-down dive): up to about 90 m/s
- Peregrine falcon in a hunting stoop: over 100 m/s, the fastest of any animal
- .30-06 bullet fired straight up, falling back down: roughly 90 m/s at terminal velocity — far below its muzzle speed, which is why a returning bullet, though still dangerous, is far less lethal than one fired horizontally
Comparing the fall of objects with different masses
In a vacuum, all objects fall at exactly the same rate regardless of mass, a fact famously demonstrated with a feather and a hammer on the Moon. In real air, however, the heavier of two same-sized objects reaches a higher terminal velocity, so it hits the ground first. The difference we observe on Earth comes entirely from air resistance, not from gravity treating the objects differently — a common misconception about free fall.
Comparing impact speed to the speed of a car
A skydiver's 60 m/s terminal velocity is equivalent to about 216 km/h — faster than a car on a motorway. Falling from a great height onto a hard surface at this speed delivers energy comparable to a high-speed vehicle crash, which is why free soloing and unroped climbing carry such extreme risk. Climber and author Clyde Soles, in discussions on forums such as rec.climbing, and biologist J. B. S. Haldane in his classic essay on size and falling, both illustrated how the same drop can be trivial for a small creature yet fatal for a large one.
Hail and the danger of large drops
Large hailstones are dangerous precisely because their size and mass give them a high terminal velocity. While tiny droplets are slowed to a harmless drift, a heavy hailstone balances gravity only at much higher speed, arriving with enough energy to shatter glass, flatten crops, and bruise orchards. The same physics that protects us from raindrops turns a large frozen sphere into a destructive projectile.
How to calculate the energy at impact
The energy an object delivers on impact is its kinetic energy, calculated as ½ · m · v², where m is mass and v is impact velocity. Because velocity is squared, impact energy grows dramatically with speed: doubling the falling speed quadruples the energy released on landing. This is why terminal velocity matters so much for safety — an object falling at 60 m/s carries far more than three times the punch of one falling at 20 m/s. For an object falling in a vacuum or before reaching terminal velocity, impact speed can be found from kinematics as v = √(2gh), where h is the falling height.
Falling speed calculator
A free fall and terminal velocity calculator lets you estimate impact speed, time to fall, and terminal velocity from an object's mass, area, drag coefficient, and drop height. Such a Free Fall Calculator typically runs in the browser using JavaScript, applying the kinematic equations for the accelerating phase and the drag formula for the steady phase. Under the hood, solving for terminal velocity requires a square root, historically computed by iterative techniques such as Newton's method before electronic calculators existed. If you enjoy the physics behind motion and forces, the wider field of science — and in particular Newton's third law with real-life examples — explains why every falling body pushes on the air just as the air pushes back on it.
