Free Fall Calculator
Enter what you know about the fall (height, time or final speed), choose the planet and see the rest. Air resistance is ignored, so real objects in air fall a little slower.
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Formula
With constant gravitational acceleration g, initial downward speed u, fall time t, drop height h and final speed v:
v = u + g·th = u·t + ½·g·t²v² = u² + 2·g·h- Time from height:
t = (−u + √(u² + 2·g·h)) ÷ g
Surface gravity: Earth 9.80665 m/s² (standard gravity), Moon 1.62, Mars 3.71, Jupiter 24.79 m/s² (NASA planetary fact sheets). Feet are converted at 1 ft = 0.3048 m. Air resistance is ignored.
Worked example
Drop an object from 100 m on Earth, starting at rest. t = √(2 × 100 ÷ 9.80665) = 4.516 s, and v = 9.80665 × 4.516 = 44.29 m/s.
The same drop on the Moon: t = √(200 ÷ 1.62) = 11.11 s and v = 18 m/s.
Frequently asked questions
How do I calculate fall time from a height?
With no starting speed, t = √(2h / g). Dropped from 100 m on Earth (g = 9.80665 m/s²), t = √(200 ÷ 9.80665) = 4.516 s.
How fast is an object going when it lands?
v = u + gt, or v = √(u² + 2gh). From 100 m on Earth the impact speed is 9.80665 × 4.516 = 44.29 m/s, about 159 km/h, before air resistance.
Does mass change how fast things fall?
Not without air. Every mass falls with the same acceleration, so a feather and a hammer land together on the Moon. On the Moon (1.62 m/s²) a 100 m drop takes 11.1 s and ends at 18 m/s.
Where do the gravity values come from?
Earth uses standard gravity, 9.80665 m/s². The Moon, Mars and Jupiter use surface values of 1.62, 3.71 and 24.79 m/s² from NASA planetary fact sheets. Gravity varies slightly with location, and Jupiter has no solid surface, so its value refers to the cloud tops.