Free fall calculator
This calculator describes an object released from rest and falling freely with constant acceleration, with no air resistance. Choose what you know, enter it, and read the other two values. Real objects in air fall slower and stop speeding up at their terminal velocity.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose which value you know: fall time, drop height or impact speed.
- Enter it, with the unit, and pick the gravity.
- The other two values appear as the large results, with the speed also in km/h.
How it works
Starting from rest, the speed grows linearly, v = g·t, and the distance fallen grows with the square of time, h = ½·g·t². The calculator rewrites these to start from whichever value you know.
Worked example
Dropped from rest for 3 seconds on Earth: height = ½ × 9.80665 × 3² = 44.13 m, speed = 9.80665 × 3 = 29.42 m/s (about 106 km/h).
Tips
- On the Moon the same 3-second drop covers only 7.29 m.
- Feet are converted exactly with 1 ft = 0.3048 m.
Frequently asked questions
What formulas does it use?
For a drop from rest with constant gravity g: height h = ½ × g × t², speed v = g × t, and so t = √(2h ÷ g). Standard gravity is exactly 9.80665 m/s².
Does it include air resistance?
No. In air a falling object reaches a terminal velocity that depends on its shape, mass and the air density, so a feather and a hammer fall very differently. The results are exact only in a vacuum and are close for short drops of dense, compact objects.
How long does it take to fall 100 metres?
On Earth with standard gravity, about 4.5 seconds, reaching about 44 m/s, if there were no air resistance. Choose Drop height, enter 100 and the calculator shows the exact figures.
Can I throw the object down or up?
Not in this tool. It assumes the starting speed is zero. For a throw you need the full equations of motion with an initial velocity.
Where do the Moon and Mars values come from?
They are commonly quoted rounded surface gravities. Gravity varies with place and altitude, so use Custom if you need a specific value.