How the calculation works
A label roll is a spiral of label tape. Its length is the area of the ring between the core and the outer edge, divided by the thickness of the tape:
Length = π × (D² − d²) ÷ (4 × t)
D is the outer diameter, d the core diameter and t the thickness of label plus liner. The number of labels is the length divided by the pitch: label length plus the gap to the next label.
Example
A roll of 300 labels of 100 × 150 mm with a 3 mm gap, on a 40 mm core at 0.14 mm thickness, is about 99 mm across with 46 m of tape. The same labels on a 1″ (25 mm) core make a roll of about 94 mm.
Will the roll fit?
Two figures matter: the maximum outer diameter the printer's roll bay accepts, and the core size its roll holder takes. Both are in the printer's data sheet under “media”. See core size and roll diameter.