What this calculator does
Roll length remaining works out how much material is left on a roll, from its diameter and material thickness. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaLength = π × (outer radius² − core radius²) / thickness
The inputs explained
| Field | What to enter |
|---|---|
| Outer diameter (cm) | A number, measured in cm. Starts at 12. |
| Core (inner) diameter (cm) | A number, measured in cm. Starts at 4. |
| Material thickness (mm) | A number, measured in mm. Starts at 0.1. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with outer diameter
Every other input is held at the calculator’s starting values while outer diameter varies. Select any row to load that scenario into the calculator.