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CGS

General

Centimetre-Gram-Second System

An older metric unit system built on centimetres, grams, and seconds, predating SI, still used in physics, electromagnetism, and astrophysics contexts.

Definition

The CGS (Centimetre-Gram-Second) system is an older metric unit system built on centimetres, grams, and seconds as its base units, predating the modern SI (International System of Units), which uses metres, kilograms, and seconds instead. Although SI is now the global standard, CGS units like the dyne, erg, and gauss persist in specific fields — particularly electromagnetism, astrophysics, and older scientific literature — due to established convention and, in some cases, mathematical simplicity.

The CGS to SI Units Converter converts between CGS and SI units across force, energy, pressure, viscosity, and magnetic flux density.

Formula

There is no single formula for CGS-to-SI conversion — each physical quantity has its own fixed multiplier. Common CGS units and their SI equivalents:

Quantity CGS Unit SI Unit Conversion
Force Dyne Newton 1 dyne = 1×10⁻⁵ N
Energy Erg Joule 1 erg = 1×10⁻⁷ J
Pressure Barye Pascal 1 barye = 0.1 Pa
Magnetic Flux Density Gauss Tesla 1 gauss = 1×10⁻⁴ T

Worked Example

Converting 500 dyne (a CGS force value) to newtons:

Result = 500 × 1×10⁻⁵ = 0.005 newtons

Key Things to Know

  • Predates SI: CGS was developed before the modern International System of Units and used the smaller centimetre and gram as base units.
  • Still active in specific fields: electromagnetism and astrophysics in particular continue to report values in CGS units like gauss and erg.
  • Conversion factors are exact: unlike some approximate unit conversions, CGS-to-SI factors are precisely defined mathematical relationships.
  • Distinct from imperial units: CGS is still a metric system — it's a different scale of metric units, not a non-metric system like imperial.

Related Terms

SievertSievert (Sv)

Frequently Asked Questions

CGS units persist in certain areas of physics, particularly electromagnetism, astrophysics, and older published research, partly because some equations take a simpler form in CGS than in SI, and partly due to long-standing convention in scientific literature.
Centimetre (length), gram (mass), and second (time) — compared to SI's metre, kilogram, and second. All CGS derived units, like the dyne and erg, build from these three base units.
A dyne is the CGS unit of force, equal to 0.00001 (1×10⁻⁵) newtons — the SI unit of force. The [CGS to SI Units Converter](/cgs-si-converter/) converts between them directly.
An erg is the CGS unit of energy, equal to 0.0000001 (1×10⁻⁷) joules — the SI unit of energy.
SI is the internationally recognised standard for scientific and everyday measurement, but CGS remains in active use within specific academic subfields (particularly Gaussian-unit electromagnetism and astrophysics) due to established convention rather than official standardisation.