No Philippe, their is only the VolumeUnitConverter, which works if you have a column with the volume already calculated and want to convert it to another unit of measurment.
Which version of FME dow you have? In FME2013 I have VolumeCalculator. VolumeUnitConverter is from the FME Store.
Anyway, I would use the ExpressionEvaluator to simply make this :
v = h?r2
h would be your length
r would be the size