ConstantID

Tau mass

Atomic & nuclearMeasured

mτ = 3.167 54(21) × 10−27 kg

Value
3.167 54 × 10−27 kg
Standard uncertainty
2.1 × 10−31 kg
Relative uncertainty
6.6 × 10−5 (66 parts per million)
Status
Measured
Symbol
mτ
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# tau mass, CODATA 2022 (NIST)
tau_mass = 3.16754e-27  # kg, standard uncertainty 2.1e-31

# SciPy: scipy.constants.physical_constants['tau mass']

What it is

The rest mass of the tau, the heaviest of the three charged leptons, in kilograms.

In other units

UnitValue
CGS (g)3.167 54 × 10−24
u dalton / atomic mass unit1.907 54unit is itself measured
MeV/c² MeV / c²1776.86
GeV/c² GeV / c²1.776 86

Converted with ConstantID's unit table; digits are rounded to the precision of the value, and a long exact value is rounded only for display. The relative uncertainty is unchanged by conversion to an exactly defined unit.

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).

tau mass: CODATA values 1998–2022 relative to the 2022 value, in parts per million, with one-standard-uncertainty bars−200−1000+100+200parts per million1998200220062010201420182022

Relative uncertainty

tau mass: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻⁵10⁻⁴10⁻³1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20223.167 54(21) × 10−276.6 × 10−5 +0.0 σ of 2018
20183.167 54(21) × 10−276.6 × 10−5 +0.2 σ of 2014
20143.167 47(29) × 10−279.2 × 10−5 +0.0 σ of 2010
20103.167 47(29) × 10−279.2 × 10−5 −0.6 σ of 2006
20063.167 77(52) × 10−271.6 × 10−4 +0.0 σ of 2002
20023.167 77(52) × 10−271.6 × 10−4 −0.2 σ of 1998
19983.167 88(52) × 10−271.6 × 10−4

“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).

Related constants

Atomic & nuclear λ¯C,τ Reduced tau Compton wavelength 1.110 538(75) × 10−16 m Atomic & nuclear λC,τ Tau Compton wavelength 6.977 71(47) × 10−16 m Atomic & nuclear mτ/me Tau-electron mass ratio 3477.23(23) Atomic & nuclear mτc2 Tau energy equivalent 1776.86(12) MeV Atomic & nuclear mτc2 Tau mass energy equivalent 2.846 84(19) × 10−10 J Atomic & nuclear mτ Tau mass in u 1.907 54(13) u Atomic & nuclear M(τ) Tau molar mass 1.907 54(13) × 10−3 kg mol−1 Atomic & nuclear mτ/mμ Tau-muon mass ratio 16.8170(11)