Command-line script

The script pint-convert allows a quick conversion to a target system or between arbitrary compatible units.

By default, pint-convert converts to SI units:

$ pint-convert 225lb
225 pound = 102.05828325 kg

use the –sys argument to change it:

$ pint-convert --sys US 102kg
102 kilogram = 224.871507429 lb

or specify directly the target units:

$ pint-convert 102kg lb
102 kilogram = 224.871507429 lb

The input quantity can contain expressions:

$ pint-convert 7ft+2in
7.166666666666667 foot = 2.1844 m

in some cases parentheses and quotes may be needed:

$ pint-convert "225lb/(7ft+2in)"
31.3953488372093 pound / foot = 46.7214261353 kg/m

If a number is omitted, 1 is assumed:

$ pint-convert km mi
1 kilometer = 0.621371192237 mi

The default precision is 12 significant figures, it can be changed with -p, but note that the accuracy may be affected by floating-point errors:

$ pint-convert -p 3 mi
1 mile = 1.61e+03 m

$ pint-convert -p 30 ly km
1 light_year = 9460730472580.80078125 km

Some contexts are automatically enabled, allowing conversion between not fully compatible units:

$ pint-convert 540nm
540 nanometer = 5.4e-07 m

$ pint-convert kcal/mol
$ 1.0 kilocalorie / mole = 4184 kg·m²/mol/s²

$ pint-convert 540nm kcal/mol
540 nanometer = 52.9471025594 kcal/mol

With the uncertainties package, the experimental uncertainty in the physical constants is considered, and the result is given in compact notation, with the uncertainty in the last figures in parentheses:

$ pint-convert Eh eV
1 hartree = 27.21138624599(5) eV

The precision is limited by both the maximum number of significant digits (-p) and the maximum number of uncertainty digits (-u, 2 by default):

$ pint-convert -p 20 Eh eV
1 hartree = 27.211386245988(52) eV

$ pint-convert -p 20 -u 4 Eh eV
1 hartree = 27.21138624598847(5207) eV

The uncertainty can be disabled with -U):

$ pint-convert -p 20 -U Eh eV
1 hartree = 27.211386245988471444 eV

Correlations between experimental constants are also known, and taken into account. Use -C to disable it:

$ pint-convert --sys atomic m_p
1 proton_mass = 1836.15267344(11) m_e

$ pint-convert --sys atomic -C m_p
1 proton_mass = 1836.15267344(79) m_e

Again, note that results may differ slightly, usually in the last figure, from more authoritative sources, mainly due to floating-point errors.