Fluid ounces infelicity

[Max Rabkin]

<Taejo> tibid: convert 40 oz to millilitres
<tibid> Taejo: I don't think 40 oz can be converted to millilitres
<Taejo> tibid: convert 40 fl oz to millilitres
<tibid> Taejo: I don't think 40 fl oz can be converted to millilitres
<Taejo> tibid: convert 40 floz to millilitres
<tibid> Taejo: 40 floz = 1182.9412 millilitres
<Taejo> tibid: convert 40 fluid ounces to millilitres
<tibid> Taejo: I can't do that: Unknown unit 'fluid

Of all of these, I think "floz" is the least common name for the unit, yet it is the only one that works.