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Conversion

Acceleration Unit Converter (m/s² ↔ ft/s² ↔ g ↔ Gal)

Acceleration is the rate of change of velocity, measured in SI by **metres per second squared (m/s²)**. Different fields use different units: automotive — **km/h per second** or **mph per second** (the "0–100" and "0–60" times); aerospace, biomechanics and crash testing — **g** (standard gravity, exactly 9.80665 m/s² by CGPM 1901); geophysics and gravimetry — **Gal** (1 Gal = 1 cm/s² = 0.01 m/s², after Galileo) with **mGal** (10⁻⁵ m/s²) for microgravity surveys; older imperial engineering — **ft/s²**. This tool converts instantly across all seven and shows the full table side-by-side for cross-checking.

Live value in every acceleration unit

m/s² Metre per second² (SI)
ft/s² Foot per second² (imperial)
g Standard gravity g
Gal Gal (CGS)
mGal Milligal mGal
km/h/s Kilometre/hour per second (km/h/s)
mph/s Mile/hour per second (mph/s)

Tip: 1 g = 9.80665 m/s² (CGPM 1901, exact), 1 ft/s² = 0.3048 m/s² (exact), 1 Gal = 0.01 m/s². A typical sedan going 0–100 km/h in 8 seconds averages roughly 0.35 g.

  • m/s² SI base unit — physics, structural dynamics, mechanics formulas
  • g Aerospace G-force, automotive crash testing, human physiological limits
  • Gal Geophysics, gravity surveys, seismographs (1 Gal = 1 cm/s²)
  • mGal Microgravity surveys, oil & gas exploration, satellite gravimetry
  • km/h/s Automotive 0–100 km/h acceleration estimates
  • mph/s US automotive industry (0–60 mph) testing

Formula

Reference unit: 1 m/s² (SI base). Exact conversion factors (each unit → m/s²): 1 m/s² = 1 m/s² 1 ft/s² = 0.3048 m/s² (exact; international foot) 1 g = 9.806 65 m/s² (exact; CGPM 1901 standard gravity) 1 Gal = 0.01 m/s² = 1 cm/s² (CGS, named after Galileo) 1 mGal = 10⁻⁵ m/s² (microgravity surveys) 1 km/h/s = 1000 / 3600 m/s² ≈ 0.2778 m/s² 1 mph/s = 1609.344 / 3600 m/s² ≈ 0.4470 m/s²

Frequently asked

A car does 0–100 km/h in 7 seconds — how many g is that?

**Short answer**: about 0.405 g on average. **Working**: 100 km/h ÷ 7 s = 14.29 km/h/s. Convert: 14.29 × (1000/3600) = 3.97 m/s²; divide by 9.80665 = **0.405 g**. **Context**: (a) average sedan (0–100 in 10 s): 0.28 g; (b) performance saloon (0–100 in 6 s): 0.47 g; (c) sports car (0–100 in 3 s): 0.94 g; (d) Formula-1 launch: > 1.5 g (limited only by tyre grip). **Caveat**: this is an *average*. Actual instantaneous values are higher in early gears (clutch engagement) and drop near zero between gearshifts. **Lateral vs longitudinal**: 0.4 g longitudinal is comfortable; tyre grip on dry asphalt with normal tyres (µ ≈ 0.7–0.9) caps maximum launch acceleration at ~0.7–0.9 g before wheelspin.

What is a Gal, and how does it relate to g?

**Gal** (named after Galileo Galilei) is the CGS unit of acceleration: **1 Gal = 1 cm/s² = 0.01 m/s²**. **vs g**: 1 g = 9.80665 m/s² = 980.665 Gal — so 1 g is roughly 981 Gal. **Where it's used**: geophysics (gravity surveys), seismographs, crustal deformation monitoring. **Why?** Earth gravity anomalies are typically tracked in mGal (10⁻⁵ m/s²) — salt domes 10–30 mGal, deep ocean plains down to −50 mGal, Mount-Everest area −100 mGal because of thin crust. In m/s² these numbers shrink to ~0.0001 m/s², which is awkward. **Modern satellite gravimetry** (GRACE, GRACE-FO) operates at μGal (10⁻⁸ m/s²) sensitivity, measuring groundwater level, ice-sheet mass change and pre- and post-earthquake crustal motion. **Note**: Gal is not an SI-accepted unit (ISO 80000-3:2019 classifies it as "historical / professional"), but it is the working unit of geophysics.

How many g can a human withstand?

**Depends on direction, duration and frequency**. **Short term (< 1 s)**: (a) **+Gz** (head-to-foot, gravity pushed towards the feet): fighter pilots in anti-g suits sustain 9 g for several seconds; (b) **−Gz** (foot-to-head): 3 g is enough to cause "red-out" (visual disturbance); (c) **+Gx** (chest-to-back, e.g. rocket launch): tolerable up to 25 g for several seconds; (d) **+Gy** (sideways): less studied but small visual effect. **Crash transient (millisecond)**: (a) typical car occupant with airbag: ~50 g; (b) Formula-1 driver Romain Grosjean at Bahrain 2020: ~67 g (survived); (c) lethal threshold typically 100 g sustained > 50 ms. **Sustained (hours)**: > 3 g is untenable (circulatory effects). **Roller-coaster design limit**: ~5 g for a few seconds to avoid harm to children and the elderly. **Reference**: Stapp (1957) rocket-sled experiments — J. P. Stapp endured 46.2 g for 1.1 s, a foundational benchmark in human biomechanics.

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