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CGS versus SI

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Warning  If hard core NMR or physics theory is not to your taste, please do not read any further!

The SI or International System of Units versus the CGS or Centimetre–gram–second system of units is a constant source of confusion in the field of NMR. Both are based on the metric system, however the differences can result in quite different forms of the fundamental NMR equations. An example of this is Tesla versus Gauss units for the magnetic field strength.

Units of measurement

Quantity Symbol SI unit CGS unit SI to CGS conversion factor
Name Symbol Base units Name Symbol Base units
length L metre m centimetre cm 10−2
mass m kilogram kg gram g 10−3
time t second s second s 1
velocity v metre per second m⋅s−1 centimetre per second cm⋅s−1 10−2
acceleration a Metre per second squared m⋅s−2 Gal gal cm⋅s−2 10−2
force F Newton N kg⋅m⋅s−2 dyne dyn g·cm·s−2 10−5
energy E Joule J kg⋅m2·s−2 erg erg g·cm2·s2 10−7
power P Watt W kg⋅m2·s−3 erg per second erg⋅s−1 g·cm2·s−3 10−7
magnetic flux density (B-field) B Tesla T kg·s−2·A−1 Gauss Gs esu·cm−2 10−4
magnetic flux density (H-field) H Amperes per metre A·m−1 Oersted Oe g·cm·s−2 4π/1000
magnetic flux ΦB Weber Wb kg·m2·s−2·A−1 Maxwell Mx esu 10−8

Constants

Constant Symbol SI unit CGS unit SI to CGS conversion factor
Definition Value Base units Definition Value Base units
magnetic force constant kA µ0·(4π)−1 10−7 kg⋅m·s−2·A−3 1 4π·µ0−1
magnetic constant µ0 µ0 4π·10−7 kg·m·s−2·A−3 1 µ0−1