CGS versus SI

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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.

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