Free Fall Calculator
Free fall is what an object does when gravity is the only force acting on it. Air resistance is ignored, which makes the mathematics exact and the answers a good approximation for anything dense.
Impact speed
19.8091
- Time in the air
- 2.0193
- Impact speed in km/h
- 71.3127
- Drop height in feet
- 65.6168
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
t = sqrt(2h / g) and v = g x t
- t
- Time spent falling, in seconds
- h
- Height dropped from, in metres
- g
- Acceleration due to gravity, about 9.81 metres per second squared
- v
- Impact speed just before landing, in metres per second
How to check the result by hand
- 1
Measure the drop height in metres
The height from which the object is released, not the height of the object's centre of mass at the end. Twenty metres is the default and is roughly a six storey building.
- 2
Double the height and divide by gravity
Twice twenty is forty, and dividing by 9.81 gives about 4.08. This intermediate quantity is in seconds squared.
- 3
Take the square root to get the time
The square root of 4.08 is about 2.0193 seconds. This is how long the object is in the air.
- 4
Multiply by gravity for the impact speed
9.81 times 2.0193 is about 19.8091 metres per second. Speed grows linearly with time, so doubling the fall time doubles the speed.
- 5
Convert to kilometres per hour if it reads better
Multiply metres per second by 3.6. The default example lands at about 71.3127 kilometres per hour, which is a speed most people can picture.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Free Fall page.