Guide

Acceleration and g-force

In engineering a lower-case g stands for standard gravity, not for the gram. That double meaning is one of the most common sources of error in datasheets.

Standard gravity as a defined constant

Standard gravity is defined exactly as 9.80665 m/s². It is not a local measurement but a convention that creates comparability. Actual gravitational acceleration varies with latitude, altitude and local rock density and therefore deviates from this value.

What g-force means

A figure of “2 g” means an acceleration twice standard gravity, i.e. 19.6133 m/s². It describes an acceleration, not a force, even though the term force appears in the name. For an actual force the mass must be known as well, because force is mass times acceleration.

Gal and feet per second squared

The gal is an older unit from geophysics and equals exactly 0.01 m/s². It is used in gravimetry because local variations in gravitational acceleration are stated there in small fractions of a gal. Feet per second squared comes from the Anglo-American system and equals exactly 0.3048 m/s².

Acceleration is not velocity

Acceleration describes the change of velocity per unit of time, not the velocity itself. A vehicle travelling at 100 km/h has a velocity of about 27.78 m/s and an acceleration of zero as long as its speed does not change. When braking, the acceleration becomes negative without the unit changing.

Matching conversions

Standard gravity to Metre per second squaredg → m/s²Acceleration Metre per second squared to Standard gravitym/s² → gAcceleration Gal to Metre per second squaredGal → m/s²Acceleration Foot per second squared to Metre per second squaredft/s² → m/s²Acceleration Kilometres per hour to Metres per secondkm/h → m/sSpeed

Unit family: Acceleration

Common questions

How much is 1 g in m/s²?

Exactly 9.80665 m/s², defined as standard gravity.

How much is 1 gal?

Exactly 0.01 m/s².

How do you convert 100 km/h to m/s?

Divide by 3.6: 100 km/h is about 27.78 m/s.

Is g-force a force?

The term describes an acceleration relative to standard gravity, not a force.

Sources

BIPM SI BrochureSI base units, prefixes and official SI context.NIST Guide to SI Appendix BNIST conversion-factor method and non-SI factors.NIST CODATA fundamental physical constantsExact defining constants such as the speed of light in vacuum.

When not to use

Do not use as the sole basis for official, medical, safety-critical or contractual decisions.

Citation

Citation note: UnitCloud, guide, sources reviewed: September 2026. Source basis: BIPM SI Brochure · NIST Guide to SI Appendix B · NIST CODATA fundamental physical constants.