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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.

CGS flavours

Note that in the CGS system, that there are different sets of units for electromagnetism. The major systems are ESU, EMU, Gaussian units, and Lorentz-Heaviside units. In NMR papers not using SI units, the EMU system is most commonly used.


Units of measurement

Quantity Symbol SI unit CGS unit (EMU) SI to CGS conversion factor
Name Symbol Base units Name Symbol Base units
length L metre m m centimetre cm cm 10−2
mass m kilogram kg kg gram g g 10−3
time t second s s second s 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 g·cm2·s−3 10−7
magnetic dipole moment μ Newton-meters per Tesla A·m2 electromagnetic unit emu abA·cm2 10−3
magnetic flux density (B-field) B Tesla T kg·s−2·A−1 Gauss Gs Mx·cm−2 10−4
magnetic flux density (H-field) H Amperes per metre A·m−1 Oersted Oe g·cm·s−2 4π·10−3
magnetic flux ΦB Weber Wb kg·m2·s−2·A−1 Maxwell Mx Mx 10−8
magnetic susceptibility χm - - (4π)−1

Constants

Constant Symbol SI unit CGS unit (EMU) 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−2 1 4π·µ0−1
magnetic constant µ0 µ0 4π·10−7 kg·m·s−2·A−2 1 µ0−1