Free Fall Calculator
How long an object takes to fall from a height and how fast it is going when it lands, ignoring air resistance.
Drop something from a height — this is when and how fast it lands.
How the free fall calculator works
Without air resistance every object falls at the same rate: after time t it has fallen ½gt² and is moving at gt. Rearranging, the time to fall a height h is √(2h ÷ g) and the impact speed is √(2gh). The calculator uses g = 9.80665 m/s²; change it in Detailed mode for the Moon (1.62) or Mars (3.72).
Air resistance matters for light or fast objects: a skydiver reaches terminal velocity near 55 m/s, so the formula only holds for the first few seconds of a real fall.
Formula: t = √(2h ÷ g) · v = √(2gh)
Worked examples
| Inputs | Time to fall | Note |
|---|---|---|
| 20 m (a six-storey building) | 2.02 s | 2.02 s, 71 km/h |
| 1 m (a table) | 0.45 s | 0.45 s |
| 100 m | 4.52 s | 4.5 s, 159 km/h — air resistance would matter |
| 20 m on the Moon | 4.97 s | g changed in Detailed mode |
FAQFrequently asked questions
Do heavy objects fall faster?
Not in a vacuum — Galileo's insight. In air, heavier objects of the same shape are less affected by drag, so a stone beats a feather. The formula ignores drag.
What is terminal velocity?
The speed at which air resistance equals weight and acceleration stops: about 55 m/s (200 km/h) for a skydiver belly-down, far less for a leaf.
How high is a 3-second fall?
½ × 9.81 × 3² ≈ 44 m. Time squared: doubling the time quadruples the height.
What is g on other planets?
Moon 1.62, Mars 3.72, Jupiter 24.8 m/s². Enter it in Detailed mode.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Institute of Standards and Technology — the US measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.