Standard Tons Displacement (std)
A widespread measure for determining a vessel's size is to give its
volume in terms of the amount of liquid hydrogen it would displace (as
if immersed in a vast sea of liquid hydrogen).
Standard tons displacement is not to be confused with the craft's
weight in metric tons (that is, its actual mass). A starship that
displaces 100 tons (as std are often confusingly referred to) may
actually weight over 1000 metric tons.
A displacement ton is actually a measure of volume rather than weight;
one displacement ton equals 13.5 kiloliters.