Free Fall CalculatorFree online science calculator — instant results, no sign-up
Calculate fall time and impact velocity from a height (no air resistance).
Sign in to save results and favorites.
About the Free Fall Calculator
The Free Fall Calculator estimates how long an object takes to fall from a specified height and how fast it is moving just before impact. It assumes the object starts from rest in a vacuum, with constant gravitational acceleration of 9.80665 m/s². Enter a height in meters to obtain fall time and impact velocity in both m/s and km/h.
- Height (m)
- The vertical distance the object falls before impact, measured in meters, with a default of 100 m.
Formula and method
h = ½gt²; t = √(2h/g); v = gt = √(2gh); v_kmh = 3.6v. For h = 100 m and g = 9.80665 m/s²: t = 4.516 s, v = 44.287 m/s, and v_kmh = 159.43 km/h.
- hVertical fall height in meters.
- gConstant downward gravitational acceleration, set to 9.80665 m/s².
- tElapsed time from release to impact, in seconds.
- vDownward impact velocity in meters per second, expressed as a positive magnitude.
- v_kmhImpact velocity magnitude in kilometers per hour.
Starting from rest, an object falling with constant acceleration travels a distance h = ½gt². The calculator solves this equation for time, computes impact velocity using √(2gh), and multiplies the unrounded velocity by 3.6 to convert m/s to km/h. Results are rounded for display.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Height100 m
Results
- Fall time4.516 s
- Impact velocity44.287 m/s
- Impact velocity (km/h)159.43
- AssumptionVacuum, g = 9.80665 m/s²
How to use the Free Fall Calculator
- 1Enter the vertical fall height in meters; use a nonnegative value.
- 2Leave the height at 100 m to reproduce the default worked example.
- 3Run the calculation using the fixed vacuum assumption and g = 9.80665 m/s².
- 4Read the fall time and impact velocity results: 4.516 s, 44.287 m/s, and 159.43 km/h for the default height.
- 5Check the assumption row before applying the results to a real-world fall.
Reading your result
Fall time is the elapsed time between release from rest and impact; for 100 m, it is 4.516 s. Impact velocity is the downward speed immediately before contact, reported as 44.287 m/s. Impact velocity (km/h) reports that same speed in different units: 159.43 km/h. The assumption row, “Vacuum, g = 9.80665 m/s²,” identifies the idealized conditions used, not an additional calculated result.
Limitations
The model assumes release from rest, no air resistance or buoyancy, and constant gravity throughout the fall. Actual fall time and impact speed depend on local gravity, object shape, surrounding air, and any initial motion. The model does not account for terminal velocity and becomes less suitable for heights where gravity changes appreciably. Negative heights are outside its domain. Impact velocity does not determine impact force without information about how the object stops.
Common questions
Does the object's mass change the calculated fall time?+
No. In this vacuum model, all objects released from rest at the same height have the same gravitational acceleration, so mass is not needed to calculate fall time or impact velocity.
Why might a real object dropped from 100 m take longer than 4.516 s?+
Air resistance opposes downward motion and generally increases fall time while reducing impact speed. The calculator excludes this effect, so its 44.287 m/s impact velocity is an idealized result.
Can I use this calculator for an object thrown downward?+
Not directly. This tool assumes zero initial velocity; a thrown object requires equations that include its initial velocity.
Why is gravity fixed at 9.80665 m/s²?+
That value is standard gravity, a conventional reference used for calculations near Earth's surface. Local gravity varies with location and altitude, but this calculator does not accept a custom gravity input.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
You might also like
Velocity Calculator
Calculate velocity from distance and time (v = d / t).
Acceleration Calculator
Calculate acceleration from the change in velocity over time (a = Δv / t).
Projectile Range
Calculate the horizontal range of a projectile launched from ground level.
Speed, Distance, Time
Solve speed = distance ÷ time — enter distance and time to get speed.
Kinetic Energy
Calculate kinetic energy from mass and velocity (KE = ½mv²).
Gravitational Potential Energy
Calculate potential energy from mass, height and gravity (PE = mgh).
Results are estimates for informational purposes and are not financial, medical or legal advice.