ConstantID

Atomic unit of velocity

UnitsMeasured

a0Eh/ℏ = 2.187 691 262 16(34) × 106 m s−1

Value
2.187 691 262 16 × 106 m s−1
Standard uncertainty
3.4 × 10−4 m s−1
Relative uncertainty
1.6 × 10−10 (155 parts per trillion)
Status
Measured
Symbol
a0Eh/ℏ
Source
CODATA 2022 via NIST · NIST entry

Use in a calculation

# atomic unit of velocity, CODATA 2022 (NIST)
atomic_unit_of_velocity = 2.18769126216e6  # m s^-1, standard uncertainty 0.00034

# SciPy: scipy.constants.physical_constants['atomic unit of velocity']

What it is

The unit of velocity in the Hartree system of atomic units, where the electron mass, the elementary charge, ħ and 4πε₀ are all set to 1. Its value here is the SI equivalent of one atomic unit.

In other units

UnitValue
CGS (cm s−1)218 769 126.216
km/h kilometre per hour7 875 688.543 78
mph mile per hour4 893 725.980 14
kn knot4 252 531.611 11
ft/s foot per second7 177 464.770 87
km/s kilometre per second2187.691 262 16
mi/s mile per second1359.368 327 82
c speed of light0.007 297 352 564 35

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).

atomic unit of velocity: CODATA values 1998–2022 relative to the 2022 value, in parts per billion, with one-standard-uncertainty bars−6−4−20+2+4+6parts per billion1998200220062010201420182022

Relative uncertainty

atomic unit of velocity: relative standard uncertainty in each CODATA adjustment, logarithmic scale10⁻¹⁰10⁻⁹10⁻⁸1998200220062010201420182022
CODATAValue (uncertainty)Relative uncertaintyChange from previous
20222.187 691 262 16(34) × 1061.6 × 10−10 −4.5 σ of 2018
20182.187 691 263 64(33) × 1061.5 × 10−10 +1.7 σ of 2014
20142.187 691 262 77(50) × 1062.3 × 10−10 −1.4 σ of 2010
20102.187 691 263 79(71) × 1063.2 × 10−10 +6.5 σ of 2006
20062.187 691 2541(15) × 1066.9 × 10−10 −1.3 σ of 2002
20022.187 691 2633(73) × 1063.3 × 10−9 +1.3 σ of 1998
19982.187 691 2529(80) × 1063.7 × 10−9

“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).