There are 16.3 cubic centimetres (cc) to the cubic inch (ci). Glow engines are typically size in fractions of a ci and gas engines in whole ccs. Therefore:

0.40 ci = 6.52 cc
0.60 ci = 9.78 cc
0.90 ci = 14.67 cc
1.20 ci = 19.56 cc
1.50 ci = 24.45 cc
1.80 ci = 29.34 cc

... etc.