Easy to find the conversion as here:

1" are 2.54 cm, to find the volume of 1 cu.in: 2.54 cm x 2.54 cm x 2.54 cm = 16.38 cubic centimetre

To example how big are the engine in cc when the engine are at 0.40 cu.in: 16.38 cc x 0.40 cu.in = 6.552 cc

To example how big are the engine in cu.in when the engine are at 15 cc: 15 cc / 16.38 cc = 0.91 cu.in