Free Fall Calculator
Calculate free fall distance, time, and velocity using the kinematic equations v = g×t, d = ½×g×t², and v² = 2gd — solving for any unknown from any known — plus a terminal velocity calculator with air resistance, and a complete reference table showing fall times and speeds for heights from 10 feet to 30,000 feet. The free fall calculator uses the standard free fall equation with g = 9.807 m/s².
| Time | Velocity | km/h | mph | Distance | Feet |
|---|
At terminal velocity, air drag equals gravity — the object stops accelerating and falls at constant speed. Formula: v_t = √(2mg / (ρ × Cd × A))
| Object | Terminal Velocity (m/s) | km/h | mph | Notes |
|---|---|---|---|---|
| Skydiver (spread eagle) | ~55 m/s | ~198 km/h | ~123 mph | ~42.8 m/s theoretical; ~55 m/s real world |
| Skydiver (head down) | ~75 m/s | ~270 km/h | ~167 mph | Streamlined position |
| Human with parachute | ~5–7 m/s | ~18–25 km/h | ~11–15 mph | Safe landing speed |
| Baseball | ~42 m/s | ~151 km/h | ~94 mph | 145g, Cd≈0.47 |
| Golf ball | ~32 m/s | ~115 km/h | ~71 mph | Dimpled surface lowers Cd |
| Tennis ball | ~31 m/s | ~112 km/h | ~69 mph | 58g, Cd≈0.50 |
| Raindrop (3mm) | ~9 m/s | ~32 km/h | ~20 mph | Drops hit gently due to low mass |
| Cat | ~27 m/s | ~97 km/h | ~60 mph | Spreads body like a parachute |
| Feather | ~1 m/s | ~3.6 km/h | ~2.2 mph | Very high Cd, tiny mass |
| Ant | ~1 m/s | ~3.6 km/h | ~2.2 mph | Survives falls from any height! |
⚠️ No air resistance assumed. These calculations use d = ½ × g × t² and v = √(2gd) with g = 9.807 m/s². Real objects reach terminal velocity well before the speeds shown for large heights. Heights marked ★ are real-world reference points.
| Height (ft) | Height (m) | Fall Time | Velocity (mph) | Velocity (km/h) | Velocity (m/s) | Notes |
|---|---|---|---|---|---|---|
| 10 ft | 3.05 m | 0.79 s | 17.3 mph | 27.9 km/h | 7.74 m/s | One-storey window |
| 20 ft | 6.10 m | 1.12 s | 24.5 mph | 39.4 km/h | 10.94 m/s | 2-storey roof |
| 30 ft | 9.14 m | 1.37 s | 30.0 mph | 48.2 km/h | 13.40 m/s | 3-storey building |
| 40 ft | 12.19 m | 1.58 s | 34.6 mph | 55.7 km/h | 15.47 m/s | |
| 50 ft | 15.24 m | 1.76 s | 38.7 mph | 62.3 km/h | 17.30 m/s | 4–5 storey building |
| 100 ft | 30.48 m | 2.49 s | 54.8 mph | 88.2 km/h | 24.49 m/s | ★ 100 ft — common reference |
| 200 ft | 60.96 m | 3.52 s | 77.5 mph | 124.7 km/h | 34.64 m/s | 20-storey building |
| 300 ft | 91.44 m | 4.32 s | 94.9 mph | 152.7 km/h | 42.43 m/s | 30-storey building |
| 500 ft | 152.40 m | 5.57 s | 122.5 mph | 197.1 km/h | 54.75 m/s | Near typical terminal v |
| 1,000 ft | 304.8 m | 7.89 s | 173.4 mph | 278.9 km/h | 77.41 m/s | ★ How long to fall 1000 feet = 7.89 s |
| 2,000 ft | 609.6 m | 11.16 s | 245.2 mph | 394.6 km/h | 109.51 m/s | ★ How long to fall 2000 feet = 11.16 s |
| 3,000 ft | 914.4 m | 13.67 s | 300.3 mph | 483.3 km/h | 134.14 m/s | ★ How long to fall 3000 feet = 13.67 s |
| 4,000 ft | 1219.2 m | 15.78 s | 346.7 mph | 557.8 km/h | 154.94 m/s | ★ How long to fall 4000 feet = 15.78 s |
| 5,000 ft | 1524.0 m | 17.64 s | 387.7 mph | 623.8 km/h | 173.24 m/s | Burj Khalifa height (1828m≈6000ft) |
| 10,000 ft | 3048.0 m | 24.95 s | 548.0 mph | 881.9 km/h | 244.95 m/s | ★ How long to fall 10,000 feet = 24.95 s |
| 20,000 ft | 6096.0 m | 35.27 s | 775.0 mph | 1247.0 km/h | 346.41 m/s | ★ How long to fall 20,000 feet = 35.27 s |
| 30,000 ft | 9144.0 m | 43.21 s | 949.3 mph | 1527.5 km/h | 424.26 m/s | ★ Cruising altitude — 30,000 ft = 43.21 s |
How to read this table: "How long does it take to fall 1,000 feet?" → find the 1,000 ft row → 7.89 seconds, reaching 173 mph. "How long to fall 3,000 feet?" → 13.67 seconds, 300 mph. "How long to fall 10,000 feet?" → 24.95 seconds, 548 mph. All values assume free fall — no air resistance. Real skydivers reach terminal velocity (~125 mph) long before these theoretical speeds.
Table A — Free Fall Equations (v₀ = 0)
| Find | Given | Formula | Example (t=5s, g=9.807) |
|---|---|---|---|
| Velocity v | Time t | v = g × t | v = 9.807 × 5 = 49.04 m/s |
| Distance d | Time t | d = ½ × g × t² | d = ½ × 9.807 × 25 = 122.6 m |
| Velocity v | Distance d | v = √(2gd) | v = √(2×9.807×122.6) = 49.04 m/s |
| Time t | Distance d | t = √(2d/g) | t = √(2×122.6/9.807) = 5.00 s |
| Time t | Velocity v | t = v/g | t = 49.04/9.807 = 5.00 s |
| Distance d | Velocity v | d = v²/(2g) | d = 49.04²/(2×9.807) = 122.6 m |
Table B — Gravity on Other Bodies
| Body | g (m/s²) | vs Earth | Fall from 10m — time | Fall from 10m — velocity |
|---|---|---|---|---|
| Earth | 9.807 | 1.0× | 1.43 s | 14.01 m/s |
| Moon | 1.62 | 0.165× | 3.51 s | 5.69 m/s |
| Mars | 3.721 | 0.379× | 2.32 s | 8.62 m/s |
| Jupiter | 24.79 | 2.53× | 0.90 s | 22.27 m/s |
| Sun | 274.0 | 27.9× | 0.27 s | 74.07 m/s |
| Mercury | 3.70 | 0.378× | 2.32 s | 8.60 m/s |
| Venus | 8.87 | 0.905× | 1.50 s | 13.32 m/s |
Table C — Drag Coefficients (Cd)
| Shape / Object | Cd | Notes |
|---|---|---|
| Sphere | 0.47 | Smooth sphere, Reynolds ~10⁵ |
| Golf ball (dimpled) | 0.25 | Dimples reduce drag |
| Flat plate (face-on) | 1.28 | Maximum drag |
| Streamlined body | 0.04 | Teardrop shape |
| Human (spread eagle) | 1.0–1.3 | Skydiver position |
| Human (head down) | 0.7 | Streamlined position |
| Parachute (open) | 1.75 | High drag by design |
| Cylinder (long axis ↓) | 0.82 | Upright orientation |
| Cone (apex down) | 0.50 | Semi-angle 60° |
| Car (modern) | 0.25–0.35 | Varies by model |
Key Formulas
Free Fall Calculator — v=gt, d=½gt², v²=2gd
This free fall calculator computes fall distance, fall time, and fall velocity using the three kinematic free fall equations — v = g×t, d = ½×g×t², and v² = 2gd — solving for any unknown from any given value, with step-by-step working and automatic unit conversion between m/s, km/h, mph, and ft/s.
Free Fall Equations — v=gt, d=½gt², v²=2gd
Free fall is motion under gravity alone with no air resistance. On Earth, gravity g = 9.807 m/s² accelerates every falling object equally — speed increases by 9.807 m/s every second regardless of mass. Starting from rest (v₀ = 0), the three free fall equations are all you need:
These free fall formulas are three views of the same motion:
- v = g × t — the velocity formula for gravity: velocity increases linearly with time. After 1s → 9.8 m/s (35 km/h). After 2s → 19.6 m/s (70 km/h). After 3s → 29.4 m/s (106 km/h).
- d = ½ × g × t² — the free fall distance formula: distance is proportional to t² (parabolic). After 1s → 4.9 m. After 2s → 19.6 m. After 3s → 44.1 m.
- v² = 2 × g × d — the equation of a falling object relating velocity directly to distance — no time needed.
The falling time equation is derived by rearranging d = ½gt²: t = √(2d/g). To find time from velocity: t = v/g. To find distance from velocity: d = v²/(2g). All six forms appear in the Reference tab above.
How to Calculate Free Fall — Step-by-Step
The method for the free fall calculation depends on what you know. Here are four completely worked examples showing how to calculate the velocity of a falling object from different starting information.
Example 1 — 3-Second Free Fall: How far does an object fall in 3 seconds?
- Known: t = 3 s, g = 9.807 m/s², v₀ = 0
- Apply free fall distance formula: d = ½ × g × t² = ½ × 9.807 × 3² = ½ × 9.807 × 9 = 44.13 m
- Apply free fall velocity formula: v = g × t = 9.807 × 3 = 29.42 m/s
- Convert: 29.42 m/s = 105.9 km/h = 65.8 mph = 96.5 ft/s
- Convert distance: 44.13 m = 144.8 ft = 0.0441 km
Example 2 — How fast after falling 100 feet?
- Convert: 100 ft × 0.3048 = 30.48 m
- Apply v² = 2gd: v² = 2 × 9.807 × 30.48 = 597.9 → v = √597.9 = 24.45 m/s
- Find time: t = √(2d/g) = √(2×30.48/9.807) = √(6.218) = 2.49 s
- Convert: 24.45 m/s = 88.0 km/h = 54.7 mph
- You hit the ground at 54.7 mph after 2.49 seconds.
Example 3 — How long to fall 1,000 feet? (A common search query)
- Convert: 1,000 ft × 0.3048 = 304.8 m
- Apply t = √(2d/g) = √(2 × 304.8 / 9.807) = √(62.17) = 7.89 s
- Apply v = g × t = 9.807 × 7.89 = 77.4 m/s = 173 mph = 278.9 km/h
- Note: This is theoretical — air resistance limits real objects to ~55 m/s (123 mph) for a person.
Example 4 — How far do you fall in 6 seconds?
- Known: t = 6 s, g = 9.807 m/s², v₀ = 0
- Apply d = ½ × g × t² = ½ × 9.807 × 36 = 176.5 m = 579 ft
- Apply v = g × t = 9.807 × 6 = 58.8 m/s = 211.7 km/h = 131.6 mph
How Fast Does Something Fall? — Speed at Common Heights
Using the free fall equation v = √(2gd), here is how fast objects fall from common heights. These represent the free fall speed without air resistance — the theoretical maximum the velocity of a falling object can reach:
| Height | Fall Time | Speed (mph) | Speed (km/h) | Speed (m/s) |
|---|---|---|---|---|
| 10 ft (3.05 m) | 0.79 s | 17.3 mph | 27.9 km/h | 7.74 m/s |
| 100 ft (30.48 m) | 2.49 s | 54.8 mph | 88.2 km/h | 24.49 m/s |
| 1,000 ft (304.8 m) | 7.89 s | 173.4 mph | 278.9 km/h | 77.41 m/s |
| 3,000 ft (914.4 m) | 13.67 s | 300.3 mph | 483.3 km/h | 134.1 m/s |
| 10,000 ft (3,048 m) | 24.95 s | 548.0 mph | 881.9 km/h | 244.9 m/s |
| 30,000 ft (9,144 m) | 43.21 s | 949.3 mph | 1,527 km/h | 424.3 m/s |
Without air resistance, a 100-foot fall reaches 54.8 mph and a 1,000-foot fall would reach 173 mph — but real objects never reach these speeds due to air resistance. A person reaches terminal velocity around 55 m/s (125 mph) after about 450 m (1,476 ft) — so speeds above ~125 mph in the table are physically unreachable in air.
Terminal Velocity — When Air Resistance Stops Acceleration
As a falling object speeds up, air resistance (drag) increases proportionally to v². At terminal velocity, drag exactly equals gravitational force — net force becomes zero and the object stops accelerating, falling at constant speed. The terminal velocity formula is:
A skydiver in spread-eagle position (m=80kg, Cd=1.0, A=0.7m²) reaches terminal velocity ≈ 55 m/s (125 mph) — this takes about 450 meters and 10–12 seconds of falling. In head-down position: terminal velocity ≈ 75 m/s (167 mph). With an open parachute (A≈30m²): terminal velocity ≈ 6 m/s (13 mph) — a safe landing speed.
Why do cats survive falls from great heights? They spread their legs to increase cross-sectional area, reducing their terminal velocity to about 27 m/s (60 mph), and then relax their bodies further. Ants have an even lower terminal velocity (~1 m/s) and can survive falls from any height without injury.
Free Fall with Initial Velocity — Thrown Objects
When an object has initial velocity v₀ ≠ 0, use the extended free fall equations:
v = v₀ + g×t— final velocityd = v₀t + ½gt²— displacementv² = v₀² + 2gd— velocity from distance
Example 1 — Ball thrown downward at 10 m/s from a 50m height
- v₀ = 10 m/s (downward), d = 50 m, g = 9.807 m/s²
- Use d = v₀t + ½gt²: 50 = 10t + ½(9.807)t² → 4.9035t² + 10t − 50 = 0
- Quadratic: t = (−10 + √(100 + 4×4.9035×50)) / (2×4.9035) = (−10 + √1080.7) / 9.807 = (−10 + 32.87) / 9.807 = 2.33 s
- Final velocity: v = 10 + 9.807 × 2.33 = 32.85 m/s = 73.5 mph
Example 2 — Ball thrown upward at 15 m/s
- v₀ = −15 m/s (upward), sign convention: down = positive
- Time to peak: t_peak = v₀/g = 15/9.807 = 1.53 s
- Max height: h = v₀²/(2g) = 225/(2×9.807) = 11.47 m
- Time to fall back to start: same 1.53 s (symmetric)
- Total air time: 2 × 1.53 = 3.06 s
Free Fall on Other Planets
Gravitational acceleration g varies dramatically by planet. The same 10-meter drop takes 1.43s on Earth but 3.51s on the Moon (2.5× slower) and only 0.90s on Jupiter (1.6× faster). The free fall equation d = ½gt² shows that fall time scales as 1/√g.
| Body | g (m/s²) | Fall 10m — time | Fall 10m — velocity | vs Earth |
|---|---|---|---|---|
| Earth | 9.807 | 1.43 s | 14.0 m/s (50.4 km/h) | — |
| Moon | 1.62 | 3.51 s | 5.7 m/s (20.5 km/h) | 2.5× slower |
| Mars | 3.721 | 2.32 s | 8.6 m/s (31.0 km/h) | 1.6× slower |
| Jupiter | 24.79 | 0.90 s | 22.3 m/s (80.2 km/h) | 1.6× faster |
| Sun | 274.0 | 0.27 s | 74.1 m/s (266.7 km/h) | 5.3× faster |
Common Mistakes in Free Fall Calculations
Mistake 1 — Forgetting the ½ in d = ½gt²
- ❌ Wrong: d = g × t² = 9.807 × 9 = 88.26 m (for 3s fall)
- ✅ Correct: d = ½ × g × t² = ½ × 9.807 × 9 = 44.13 m
- Omitting the ½ gives exactly double the correct distance.
Mistake 2 — Applying Power Rule to 1/x (wrong example — not this page)
- ❌ Wrong: Using d = gt² instead of d = ½gt²
- ✅ Correct: d = ½ × g × t² — the kinematic equation from integration of v = gt
Mistake 3 — Using g = 10 instead of 9.807
- g = 10 m/s² is an approximation giving ~2% error. Use g = 9.807 m/s² (exact SI) for accurate answers.
- Error example: 3s fall → d = ½×10×9 = 45 m (wrong) vs ½×9.807×9 = 44.13 m (correct)
Mistake 4 — Ignoring Air Resistance for Long Falls
- The free fall equations v = gt and d = ½gt² only apply in a vacuum (or for very short, slow falls).
- For falls over ~100m, air resistance becomes significant and objects approach terminal velocity.
- The 1,000-foot free fall table shows 173 mph — but a real person caps at ~125 mph (terminal velocity).
Mistake 5 — Unit Confusion (feet vs meters)
- ❌ Wrong: Treating 100 feet as 100 meters in t = √(2d/g)
- ✅ Correct: Convert first — 100 ft × 0.3048 = 30.48 m, then t = √(2×30.48/9.807) = 2.49 s
- Using 100 instead of 30.48 gives t = 4.51 s — nearly double the correct answer.
Worked Examples — 8 Complete Problems
1. How far does an object fall in 3 seconds?
- d = ½ × g × t² = ½ × 9.807 × 9 = 44.13 m = 144.8 ft
- v = g × t = 9.807 × 3 = 29.4 m/s = 65.8 mph
2. How fast after falling 100 feet?
- 100 ft = 30.48 m
- v = √(2 × 9.807 × 30.48) = √597.9 = 24.45 m/s = 54.7 mph
- t = 24.45 / 9.807 = 2.49 s
3. How long to fall 1,000 feet?
- 1,000 ft = 304.8 m
- t = √(2 × 304.8 / 9.807) = √62.17 = 7.89 s
- v = 9.807 × 7.89 = 77.4 m/s = 173 mph
4. Terminal velocity of a skydiver (spread eagle)
- m = 80 kg, Cd = 1.0, A = 0.70 m², ρ = 1.225 kg/m³, g = 9.807 m/s²
- v_t = √(2 × 80 × 9.807 / (1.225 × 1.0 × 0.70)) = √(1569.1 / 0.8575) = √(1829.8) = 42.78 m/s = 154 km/h = 95.8 mph
- Verify: F_drag = ½ × 1.225 × 42.78² × 1.0 × 0.70 = 784.5 N; F_gravity = 80 × 9.807 = 784.6 N ✓
5. Free fall on the Moon from 10m
- g_moon = 1.62 m/s²
- t_moon = √(2×10/1.62) = √12.35 = 3.51 s (vs Earth: 1.43 s)
- v_moon = √(2×1.62×10) = √32.4 = 5.69 m/s = 20.5 km/h (vs Earth: 14.0 m/s)
6. How far do you fall in 6 seconds?
- d = ½ × 9.807 × 36 = 176.5 m = 579 ft
- v = 9.807 × 6 = 58.8 m/s = 211.7 km/h = 131.6 mph
7. Object thrown downward at 10 m/s from 50m height — time to ground
- 50 = 10t + ½(9.807)t² → 4.9035t² + 10t − 50 = 0
- t = (−10 + √(100 + 980.7)) / 9.807 = (−10 + √1080.7) / 9.807 = 22.87 / 9.807 = 2.33 s
- v = 10 + 9.807 × 2.33 = 32.85 m/s = 73.5 mph
8. At what height does a falling object reach 60 mph (26.82 m/s)?
- v = 60 mph = 60 × 0.44704 = 26.82 m/s
- d = v²/(2g) = 26.82² / (2 × 9.807) = 719.3 / 19.614 = 36.7 m = 120.4 ft
- t = v/g = 26.82 / 9.807 = 2.74 s
Frequently Asked Questions — Free Fall Calculator
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