Free fall calculator
Impact speed and fall time from a height or from a duration.
Fill in the fields and the result will appear here automatically.
Calculate motion released from rest with constant positive gravitational acceleration and no drag. Height mode gives elapsed time and speed at the lower point. Time mode gives downward distance and speed after that interval; it is an impact speed only if a surface is placed there. Mass cancels in this model.
How it works
Formula and logic
From rest: h=g·t²/2, t=√(2 h/g), v=g·t=√(2 gh). Kinetic energy per kilogram is v²/2=gh. Height and time describe a positive fall interval; initial velocity is not entered.
Example
A fall from twenty metres takes 2.02 seconds and lands at 19.8 m/s — that is 71 km/h.
Fields and units
- What is known — list option
- Height — m
- Fall time — s
- Gravitational acceleration — m/s²
How to use
- — Choose what you know: the height or the fall time.
- — Remember the air: for light or fluttering objects this overstates the speed.
- — For another location enter the appropriate g. The 9.80665 m/s² default is a conventional standard, not measured gravity at every point on Earth.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- OpenStax: free fall without drag
- Limitation
- Release from rest, constant g and no air resistance. Initial velocity, object shape and changes of g with altitude are not modelled; this does not describe a person’s jump or parachute operation.
FAQ
Does falling speed depend on mass?
Without air, no: a feather and a stone fall alike, and mass does not appear in the formula. With air the difference is enormous, but that is no longer free fall.
Why does height grow as the square of time?
Because the speed builds up evenly and the distance covered is the area under the speed graph. In two seconds a body falls four times as far as in one.
Can this model a parachute jump?
No. The model includes no drag, parachute deployment or changing area. Once drag matters, motion depends on air density, shape, mass and area; there is no universal 55 m/s limit or transition time.
Where does 9.80665 come from?
It is the conventional standard value used for calculations. Real gravity ranges from 9.78 at the equator to 9.83 at the poles and drops slightly with altitude.