Free Fall Calculator
Find how long an object takes to fall, how fast it hits the ground and how high it fell, on Earth or any other world.
🍎 What is Free Fall?
Free fall is the motion of an object that is acted on by gravity alone. A dropped stone, a coin released from a bridge and a ball tossed off a cliff are all treated as free fall once you ignore the air. In that idealised case the object gains the same amount of speed every second, a steady gain of about 9.8 metres per second on Earth. This calculator uses that model for an object released from rest, so you only need one of three quantities (the drop height, the fall time or the impact speed) to find the other two.
The idea is used everywhere in introductory physics and in practical estimates. Students use it to check homework, engineers use it to estimate the impact speed of a part falling from a shelf or a platform, and hobbyists use it to estimate the depth of a well or a shaft from the time a stone takes to land. Planetary scientists use the same equations with a different value of g to ask how long a lander or a dropped tool would take to fall on the Moon or Mars. Because the fall time depends on the square root of height divided by g, low gravity worlds give slow, floaty falls: a 100 m drop that takes 4.5 s on Earth takes 7.3 s on Mars and 11.1 s on the Moon.
It is worth being clear about the limits. Free fall in the strict sense means no air resistance, so the results here are vacuum results. For a compact, dense object falling a few metres the error is tiny. For a leaf, a parachutist or any fall that reaches tens of metres per second, drag changes the answer a lot and the true speed levels off at a terminal velocity. In that case use the free fall with air resistance calculator, or check the terminal velocity calculator. Also note that free fall does not require the object to move straight down: the Moon orbiting Earth is in free fall too. Here we use the simple vertical drop from rest.
This tool also shows the average speed, the distance covered in the final second, and two charts: speed against time (a straight line) and height above the ground against time (a falling parabola). The results update as you type, and every example below has a link that fills in the inputs for you.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 — Dropping a Stone from 100 m on Earth
Height h = 100 m, g = 9.80665 m/s²
Example 2 — Depth of a Well from a 3 Second Drop
Fall time t = 3 s, Earth
Example 3 — Height Needed to Hit 30 m/s
Impact speed v = 30 m/s, Earth
Example 4 — The Same 100 m Drop on Mars
Height h = 100 m, g = 3.721 m/s²
Example 5 — Impact Speed Given in km/h
Impact speed 100 km/h, Earth
❓ Frequently Asked Questions
🔗 Related Calculators
What is the free fall formula for time?
For an object dropped from rest, the fall time is t = sqrt(2h / g), where h is the height and g is gravitational acceleration. With h = 100 m and g = 9.80665 m/s2 the time is 4.516 s. Air resistance is ignored.
How do you find impact speed in free fall?
Impact speed is v = g t = sqrt(2 g h). A 100 m drop on Earth gives 44.29 m/s, about 159 km/h. The result is the vacuum speed, so a real object in air will be slower, especially if it is light or has a large area.
How do you find the height of a fall from the time?
Use h = 0.5 g t squared. A stone that takes 3 s to fall on Earth drops 0.5 x 9.80665 x 9 = 44.13 m. This is a common way to estimate the depth of a well from the splash time, ignoring the sound travel time.
What is g on Earth and on Mars?
Standard gravity on Earth is 9.80665 m/s2, and the surface gravity of Mars is 3.721 m/s2, about 38 percent of Earth. The Moon is 1.62 m/s2, Venus 8.87, Mercury 3.7 and Jupiter about 24.79 at the cloud tops.
Does mass change how fast something falls?
No. In free fall the acceleration g is the same for every mass, because weight and inertia both scale with mass. A hammer and a feather fall together in a vacuum, as shown on the Moon. In air, differences come from drag, not from mass itself.
How far does an object fall in 1, 2 and 3 seconds?
On Earth, 4.90 m, 19.61 m and 44.13 m. The distances grow as the square of time. The distance in each successive second grows by g, so the second 1 covers 4.90 m, second 2 covers 14.71 m and second 3 covers 24.52 m.
How fast is an object falling after 5 seconds?
On Earth the speed after 5 s is 49.03 m/s (about 176 km/h or 110 mph) in a vacuum. It would have fallen 122.58 m. In real air a skydiver would be below that speed because drag has already become significant.
What is the difference between free fall and falling with air resistance?
Strict free fall means only gravity acts, so speed rises forever as g t. With air drag the speed levels off at the terminal velocity. For short drops of a few metres of dense objects the difference is tiny, but it grows quickly at higher speeds.
How long does it take to fall 10 meters?
On Earth, t = sqrt(2 x 10 / 9.80665) = 1.428 s, and the impact speed is 14.00 m/s, about 50 km/h. On Mars the same drop takes 2.318 s and ends at 8.63 m/s.
Can I enter the impact speed in km/h or mph?
Yes. In Impact speed mode, choose km/h or mph in the unit selector, then type the speed. The calculator reads the number in that unit and converts it internally, then reports drop time and height. For example 100 km/h corresponds to 2.833 s and 39.34 m.
Why does the distance in the final second matter?
It shows how quickly the object is moving near impact. The last second covers h minus the distance fallen up to t minus 1 seconds. It is useful for checking a measured fall, such as video frames near the ground.