Free Fall Calculator

This calculator models the motion of an object dropped from rest under the influence of gravity alone, using g = 9.81 m/s squared. Free fall is a special case of uniform acceleration where the initial vertical velocity is zero and the only force acting is gravity. You choose whether you want to start from a known height or a known elapsed time. If you enter a height in metres, the calculator returns the final velocity at impact in m/s and km/h, and the time it takes to reach the ground. If you enter an elapsed time in seconds, the calculator returns the distance fallen and the velocity reached at that moment. The gravitational acceleration can be adjusted if you want to model free fall on another body, such as the Moon (1.62 m/s squared) or Mars (3.72 m/s squared). This tool is useful for physics students, safety engineers calculating impact speeds, and anyone curious about how fast or how far an object falls. The results assume no air resistance and a uniform gravitational field, so they represent the theoretical maximum fall speed. In practice, air resistance slows real objects and a terminal velocity is reached. For objects with an initial upward or horizontal velocity, use the Projectile Motion Calculator or SUVAT Solver instead.

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Solve from

Height

Time

Gravity (g)

m/s²

29.43 m/s

final velocity at impact

km/h105.95

Fall time3.00 s

No air resistance assumed. Adjust g for other planets (Moon: 1.62, Mars: 3.72 m/s²).

How it works

For an object dropped from rest at height h: v = sqrt(2gh) and t = sqrt(2h/g). For an object falling for a known time t: v = g × t and h = ½g × t². The calculator selects the appropriate pair of equations depending on your chosen mode. Speed in km/h is the velocity in m/s multiplied by 3.6.

Worked example

An object is dropped from 44.15 m. Final velocity = sqrt(2 × 9.81 × 44.15) = 29.43 m/s (105.95 km/h). Fall time = sqrt(2 × 44.15 / 9.81) = 3.00 s. These match the defaults pre-filled above and are consistent with the SUVAT worked example (u = 0, a = 9.81, t = 3 s).

Related calculators

SUVAT Calculator: the full kinematic equations when u is not zero.
Projectile Motion Calculator: for objects launched at an angle.
Acceleration Calculator: solve a = (v - u) / t for any variable.
Kinetic Energy Calculator: find the energy of the falling object at impact.

Frequently asked questions

What is the formula for free fall?

For an object dropped from rest, the key free fall equations are: v = sqrt(2gh) to find final velocity from height; t = sqrt(2h/g) to find fall time from height; and h = 0.5 x g x t2 to find distance fallen in time t. Here g is the acceleration due to gravity, approximately 9.81 m/s2 on Earth.

Does mass affect how fast an object falls?

In the absence of air resistance, all objects fall at the same rate regardless of mass. This was demonstrated by Galileo and confirmed by Apollo 15 astronauts dropping a hammer and feather on the Moon. In practice, air resistance creates drag that slows lighter or less dense objects more than denser ones.

What is the value of g used in this calculator?

This calculator uses g = 9.81 m/s2, which is the standard value for gravitational acceleration at sea level. The actual value varies slightly by latitude and altitude, from about 9.78 m/s2 at the equator to 9.83 m/s2 at the poles.