Introduction
Acceleration is the rate of change of velocity, measured in m/s² (SI), ft/s² (US), g (multiples of Earth gravity), or gal (geophysics). Car magazines quote 0-60 mph times; astronauts experience g-forces at launch; geophysicists measure gravity anomalies in milligals. All the same underlying quantity; different scales.
Why acceleration units exist and how they diverged
The m/s² is the SI unit — the acceleration that increases velocity by 1 m/s every second. Standard gravity (g) is 9.80665 m/s² by international agreement, though actual gravity varies from 9.78 (equator) to 9.83 (poles) due to Earth's shape and rotation. Astronauts in free-fall experience 0 g; Earth surface is 1 g; fighter-pilot high-g turns hit 9 g (about 90 m/s²).
The gal (named after Galileo) is 1 cm/s² = 0.01 m/s² — a small unit used in geodesy to map gravity variations. A milligal (0.00001 m/s²) picks up oil and mineral deposits; a microgal detects subsurface density changes at a meter scale.
How to convert acceleration
g to m/s²: multiply by 9.80665. m/s² to ft/s²: multiply by 3.281. For 0-60 mph times: final velocity 60 mph = 26.82 m/s; acceleration = 26.82 / time. A 5-second 0-60 car averages 5.36 m/s² = 0.55 g.
Units supported by this acceleration calculator
- m/s²
- ft/s²
- g-force (standard gravity)
- Gal (cm/s²)
- in/s²
- km/(h·s)
- mph/s
- milligal
Common acceleration conversion mistakes
- g as a gravitational field vs acceleration. Earth's g-field is ~9.81 N/kg at the surface; an accelerometer in free-fall reads 0 g (no force); at rest reads 1 g (up). Astronauts in orbit are not in zero gravity — they're in free-fall, which is why they feel weightless.
- Average vs peak acceleration. A car's '0-60 in 5 seconds' is average. Peak instantaneous acceleration happens in second 1-2 and can be 1.5-2× the average.
- Deceleration as 'negative acceleration.' Same units, opposite sign. Emergency braking at 1 g = -9.81 m/s². A 30-foot skid mark at 1 g deceleration implies entry speed around 30 mph.
- Gal vs Galileo. The unit is sometimes also called 'galileo' — same thing, 1 cm/s².
- g as mass multiplier. '5 g acceleration' is an acceleration; a 70 kg person experiencing 5 g feels 5 × 70 × 9.81 = 3,430 N of force (about 770 lbf). The g is acceleration; the felt weight scales accordingly.
Real-world acceleration examples
- Free-fall in vacuum (Earth): 9.81 m/s² = 1 g.
- Moon gravity: 1.62 m/s² = 0.166 g.
- Mars gravity: 3.71 m/s² = 0.378 g.
- Jupiter gravity: 24.79 m/s² = 2.53 g.
- Typical car 0-60 in 8 sec: 3.35 m/s² = 0.34 g average.
- Tesla Model S Plaid 0-60 in 1.99 s: 13.5 m/s² = 1.38 g.
- F1 braking peak: ~5 g (49 m/s²).
- Fighter jet turn: up to 9 g sustained.
- Roller coaster drop: 3-5 g.
- Astronaut at Saturn V launch: peak ~4 g.
- Bullet in rifle barrel: ~100,000 g = 980,000 m/s².
Tips for accurate acceleration conversion
- For car reviews, 0-60 mph time is the most common acceleration metric; lower is faster.
- For physiological limits, humans can tolerate brief peaks of 10+ g but sustain only 5-6 g for seconds.
- For geodesy, milligal-level maps reveal mineral deposits, salt domes, and tectonic features.
Related: Speed Converter · Force Converter · Time Converter.