How the calculation works
A roll of labels is a spiral of web wound around a core. The length of web on the roll is calculated from the area of the ring between core and outer diameter, divided by the thickness of the web:
Length = π × (D² − d²) ÷ (4 × t), where D is the outer diameter, d the core diameter and t the total thickness of label, adhesive and liner, all in millimetres.
Labels per roll = length ÷ (label length + gap) × labels across. To find the diameter for a given number of labels, the same formula is solved for D.
Real rolls are slightly looser than the theory, so keep a margin of a few percent below your labeller's maximum diameter.
Frequently asked questions
How many labels are on a roll?
It depends on the outer diameter, the core, the label length plus gap and the material thickness. Enter them in the calculator: for example, 100 mm labels with a 3 mm gap on paper (0.14 mm) on a 76 mm core fit about 4,500 labels (around 470 m of web) in a 300 mm roll.
Which label length should I enter?
The dimension in the direction the web runs through the labeller, plus the gap to the next label. For labels wound sideways, it is the width of the label.
What core size do labellers use?
76 mm (3 inch) cores are the most common for automatic labellers; 40 mm and 25 mm cores are used for small applicators and printers. Check your machine's manual.
Why is the real roll slightly bigger than calculated?
Winding tension, splices and small variations in thickness make real rolls a little looser than the theory. Keep a margin below the maximum diameter.