The circumference of the inside of a standard toilet paper roll is approximately 13.5 to 14.5 centimeters. This measurement can vary slightly between brands and manufacturing processes. To find it, you'd typically measure the diameter and then multiply by pi (π ≈ 3.14159).
The inner surface of a tp roll core, though often overlooked, can affect its friction against a dispenser spindle. A smoother surface will generally have less friction, allowing the roll to spin more freely. Conversely, a rougher or slightly textured surface might create more resistance. This can impact how easily the toilet paper dispenses, especially as the roll gets lighter. Manufacturers balance this during the tp roll test to ensure smooth operation without excessive free-spinning.