Proton gyromagnetic ratio in MHz/T

$γₚ/2π$ = 42.577 478 461(18) MHz T⁻¹

Value: 42.577 478 461 MHz T⁻¹
Standard uncertainty: 1.8 × 10⁻⁸ MHz T⁻¹
Relative uncertainty: 4.2 × 10⁻¹⁰ (423 parts per trillion)
Status: Measured
Symbol: $γₚ/2π$
Source: CODATA 2022 via NIST · NIST entry

Use in a calculation

# proton gyromagnetic ratio in MHz/T, CODATA 2022 (NIST)
proton_gyromagnetic_ratio_in_mhz_t = 4.2577478461e1  # MHz T^-1, standard uncertainty 1.8e-8

# SciPy: scipy.constants.physical_constants['proton gyromag. ratio in MHz/T']

What it is

The precession frequency, per tesla of magnetic field, of the proton, the nucleus of the hydrogen atom: the gyromagnetic ratio divided by 2π. Magnetic resonance spectroscopists use this form.

How the value changed, 1998–2022

Each point is one CODATA adjustment, plotted as its difference from the 2022 value; the bars show one standard uncertainty (an arrowhead means the bar runs off the chart).

Relative uncertainty

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	42.577 478 461(18)	4.2 × 10⁻¹⁰	−3.2 σ of 2018
2018	42.577 478 518(18)	4.2 × 10⁻¹⁰	−1.4 σ of 2014
2014	42.577 478 92(29)	6.8 × 10⁻⁹	−1.7 σ of 2010
2010	42.577 4806(10)	2.3 × 10⁻⁸	−1.4 σ of 2006
2006	42.577 4821(11)	2.6 × 10⁻⁸	+0.2 σ of 2002
2002	42.577 4813(37)	8.7 × 10⁻⁸	−0.7 σ of 1998
1998	42.577 4825(18)	4.2 × 10⁻⁸

“Change from previous” is the shift in the value divided by the standard uncertainty of the previous adjustment. Earlier values are converted into the current unit where NIST changed it (for example J s to J Hz⁻¹).