Quick answer
This free fall calculator works out the time, distance and speed of an object dropped from rest. Choose whether you know the height, the time or the final speed, and it uses the free-fall equations with g = 9.81 m/s² (or any value you choose) to find the rest.
Free fall: time, height and speed
How to Use the Free Fall Calculator
- Choose what you already know: the height, the time of the fall or the final speed.
- Enter that value in SI units.
- Keep g = 9.81 m/s² for Earth, or change it for another planet.
- Press Calculate. The result shows the answer and the formula used.
Free Fall Equations
An object in free fall starts from rest (u = 0) and speeds up at a constant rate g. These are the SUVAT equations with u = 0 and a = g.
| To find | Formula |
|---|---|
| Time from height | t = √(2h ÷ g) |
| Speed from height | v = √(2gh) |
| Height from time | h = ½gt² |
| Speed from time | v = gt |
Read more about falling objects in our kinematics guide.
Worked Example
Worked example: a dropped phone
Question: A phone slips from a balcony 12 m above the ground. How long does it fall and how fast does it hit the ground?
- t = √(2 × 12 ÷ 9.81) = √2.446 ≈ 1.56 s.
- v = √(2 × 9.81 × 12) = √235.4 ≈ 15.3 m/s.
- Converting: 15.3 × 3.6 ≈ 55 km/h.
Answer: It falls for about 1.56 s and lands at about 15.3 m/s (55 km/h).
Free Fall vs Real Falling
The calculator assumes there is no air resistance. That is accurate for dense, compact objects over short drops. For long falls or light objects, air resistance grows with speed until it balances the weight, and the object reaches terminal velocity. A skydiver, for example, levels off at roughly 55 m/s instead of speeding up forever.
Common mistake: Mass does not appear in any free-fall formula. Without air resistance, a heavy ball and a light ball dropped together land at the same time.
Learn more: read about free fall and terminal velocity explained with examples.
This free fall calculator is ideal for checking drop-test experiments and textbook questions, because it shows the formula and substitution for every answer.
Frequently Asked Questions
What value of g should I use?
Use 9.81 m/s² near Earth’s surface. Some courses round it to 9.8 or 10 m/s²; you can type any value into the calculator.
Does mass affect free fall?
No. In true free fall every object accelerates at g regardless of its mass. Differences in real life come from air resistance.
How long does it take to fall 100 metres?
Ignoring air resistance, t = √(2 × 100 ÷ 9.81) ≈ 4.5 s, and the object would be moving at about 44 m/s.