Free Fall Calculator
Calculate fall time, distance and impact speed under gravity.
Please note: Results use idealised models — point masses, no air resistance, ideal gases and uniform materials. Real experiments deviate. Use these for study and estimation, not for engineering sign-off.
What the Free Fall Calculator does
In free fall every object accelerates at the same rate regardless of mass — a fact that holds exactly in a vacuum. Distance grows with the square of time while speed grows linearly, so the last second of a long fall covers far more ground than the first.
Formula
h = ut + ½gt²v = u + gtv = √(u² + 2gh)t = (−u + √(u² + 2gh)) ÷ g
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| What do you know? | one of 3 options | Yes | — |
| Drop height | number | In some modes | Shown What do you know? is The drop height. |
| Drop height unit | one of 9 options | In some modes | Shown What do you know? is The drop height. |
| Fall time | number | In some modes | Shown What do you know? is The fall time. |
| Fall time unit | one of 6 options | In some modes | Shown What do you know? is The fall time. |
| Impact speed | number | In some modes | Shown What do you know? is The impact speed. |
| Impact speed unit | one of 5 options | In some modes | Shown What do you know? is The impact speed. |
| Initial downward velocity | number | Optional | Zero for a simple drop. Positive if thrown downwards. |
| Initial downward velocity unit | one of 5 options | Yes | — |
| Gravitational acceleration | m/s² | Optional | Standard gravity on Earth is 9.80665 m/s². The Moon is 1.62, Mars 3.72. Accepts 0 or more. |
How to use it
- Choose What do you know? and Initial downward velocity unit.
- Fill in the remaining inputs the form shows for your choice.
- Optionally add Initial downward velocity and Gravitational acceleration.
- Select Calculate.
Worked example
An object dropped from 100 m with no initial velocity.
- Height
- 100 m
- Initial velocity
- 0
- Gravity
- 9.80665
t = √(2 × 100 ÷ 9.80665) = 4.516 s, hitting at 44.29 m/s — about 159.4 km/h.
Frequently asked questions
Do heavier objects fall faster?
Not in a vacuum — a hammer and a feather land together, as demonstrated on the Moon. In air, heavier and denser objects overcome drag better and so fall faster.
What is terminal velocity?
The speed at which air resistance balances weight, after which there is no further acceleration. It is about 55 m/s for a belly-down skydiver and roughly 90 m/s head-down.