How to measure label roll diameter

Roll-geometry calculations are sensitive to diameter. A careful measurement is more valuable than adding extra decimal places to the formula.

Measure the finished outside diameter

Measure straight through the centre of the roll from one outer edge to the opposite outer edge. Keep the measuring tool perpendicular to the roll faces so you do not accidentally measure a diagonal. For soft or loosely wound stock, avoid squeezing the roll.

Use core outside diameter in roll-geometry formulas

The wound material begins at the outside surface of the core. That is why the calculator asks for core OD rather than the hole diameter. If a supplier only gives core ID, measure the core wall or the outside directly when accuracy matters.

Measure more than once

Real rolls can be slightly out of round. Measuring at two or more orientations and using a representative value can reduce error, especially on partially used or soft-wound rolls.