Conventional value of watt-90

$W_{90}$ = 1.000 000 195 53… W

Value: 1.000 000 195 53… W
Standard uncertainty: exact
Relative uncertainty: exact
Status: Exact
Symbol: $W_{90}$
Source: CODATA 2022 via NIST · NIST entry

NIST prints this exact value cut to 12 digits. ConstantID recomputes it from the defining constants: 1.000 000 195 536 554 834 989 935 918 26…

Use in a calculation

# conventional value of watt-90, CODATA 2022 (NIST)
conventional_value_of_watt_90 = 1.0000001955365548349899359182625  # W, exact

# SciPy: scipy.constants.physical_constants['conventional value of watt-90']

What it is

The size of the practical watt used in electrical metrology from 1990 to 2019 (based on K_J-90 and R_K-90), in SI watts. It is exact because the elementary charge and Planck constant are now exact.

It is built only from constants with exact values, so it is exact too.

In other units

Unit	Value
CGS (cm² g s⁻³)	10 000 001.96	exact
mW milliwatt	1000.000 196	exact
kW kilowatt	0.001 000 000 196	exact
hp horsepower (mechanical)	0.001 341 022 352	exact
PS metric horsepower	0.001 359 621 883	exact
Btu/h Btu per hour	3.412 1423	exact
kcal/h kilocalorie per hour	0.860 420 8183	exact

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.

How the value changed, 1998–2022

CODATA	Value (uncertainty)	Relative uncertainty	Change from previous
2022	1.000 000 195 53…	exact	exact
2018	1.000 000 195 53…	exact

“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).