Frame size(height) is the distance between crank axe and the end of frame saddle tube. Size is usually in inches (1 inch = 2,54cm).
Sizes can differ a bit from the final construction.
Frame size definition for children:
Age
2-4 years
3-5 years
4-6 years
5-8 years
7-11 years
10+ years
Wheel size
12”
14”
16”
20”
24”
26”+
Person height
82-100 cm
98-106 cm
104-122 cm
120-130 cm
127-142 cm
140+ cm
Crotch height
30-40 cm
36-44 cm
40-54 cm
52-59 cm
57-66 cm
64-70 cm
Frame size definition for adults: