To expand on epimetheus's comment, the 230cf your supplier quoted is actually
standard cubic feet, which refers to a quantity of substance rather than volume, and as such is convertible to
moles of helium. You can't convert it to unqualified liters because volume of a gas is dependent on temperature and pressure according to the
combined gas law. You can, however, convert SCF to standard cubic meters because, like SCF, an SCM is defined as a
unit of volume at a standardized temperature and pressure.
But all that isn't really necessary to answer your question, because unless you're buying cryogenic gas (which you aren't), the temperature inside the gas
bottle is the same as outside, which means that you only need to know the ratio of
bottle pressure to atmospheric pressure in order to determine how many SCF of helium are in that 5L
bottle. And fortunately, there is a
unit of pressure called the
Atmosphere that is roughly equivalent to atmospheric pressure on Earth at sea
level. So if you identify the pressure of their usual 5L helium
bottle in atm (or bar, the units are nearly equivalent), you can use that directly as the ratio of expansion when you crack open the
bottle and all that He rushes out into the air--well, assuming your atmospheric conditions inside your
venue are reasonably close to
STP, which they probably are if you're not at a very high elevation. You can also adjust the ratio based on another target pressure--say you want to fill a football to 5psig (~19.7psia), you can use this pressure to determine the quantity of helium in scf or scm that will be required.
Nerdiness aside, here's the bottom
line:
here's an example: if the 5L
bottle of Helium has an internal pressure of 250atm, then it contains 5L * 250 = 1250L @
STP = 1.25 SCM = 43 SCF. According to wikipedia, standard pressure for bottled gases is
200-400 atm, so based on that range they're requesting a quantity of somewhere between 34.3 and 68.8 SCF.
)
