Roll Length from Diameter Calculator
Estimate wound film length from roll outside diameter, core outside diameter and film thickness. Use the core’s outer surface diameter, where the film starts winding.
Use a saved product specification (optional)
Enter your values
First time using this calculator?
Replace the example values with figures from your supplier sheet or measurements. Choose the unit beside each value. Results update as you type; fix any highlighted field before using the result.
GSM means grams per square metre. Net weight excludes the core and other packaging. MOQ means the minimum order quantity. An optional field can stay blank unless the result you need depends on it.
Prices keep the selected currency; changing its label does not convert an exchange rate. Save or export the result after checking your inputs.
Measure the outside of the core, not its bore.
Help with film thickness
Use the measured or specified material thickness. One micron (µm) is one thousandth of a millimetre.
Estimated roll length
Geometric estimate: assumes uniform thickness, a tightly wound roll and no entrained air. Actual running length may differ.
Core OUTER diameter is used; a nominal core bore is not a substitute.
Length (m) = π × (roll OD² − core OD²) ÷ (4 × thickness); OD in mm, thickness in µm
π × (350² − 90²) ÷ (4 × 80) = 1,123.119374 mSaved calculations stay in this browser. No account or cloud backup is created.
Save to a product project (optional)
Choose or create a saved product project ↗This is an illustrative example. Saved or transferred values must be checked against your job.
Calculated from your inputs. Confirm specifications with your supplier.
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Vary one input and inspect estimated roll length
All other entered inputs stay fixed. Ranges are your scenarios, not statistical confidence or supplier performance predictions. This uses the same validated calculator engine.
The formula, made clear.
The wound film occupies an annular cross-section around the core. Its area equals the total length multiplied by film thickness when the winding is ideal and tightly packed. Subtracting the core cross-section from the roll cross-section and dividing by thickness gives length. Both diameters are expressed in millimetres in the displayed formula. The core inside diameter, often used to describe the machine shaft size, is not interchangeable with the required core outside diameter.
How to use this calculator
- 01
Measure the roll outside diameter and the outside diameter of the empty core.
- 02
Enter total film thickness, including the laminate thickness rather than one layer alone.
- 03
Treat the calculated length as a geometric estimate and compare with a meter counter or weight check when available.
A calculation you can check
The example estimates the film length occupying the annular space between a known core and a measured roll diameter.
- Roll outer diameter
- 350 mm
- Core OUTER diameter
- 90 mm
- Film thickness
- 80 µm
π × (350² − 90²) ÷ (4 × 80) = 1,123.119374 mCheck the displayed formula and units against your quotation. Use measured GSM, net weight and actual layout dimensions where available. Default densities are planning assumptions, not certified material properties. Calculated cost does not certify strength, compatibility or safe loading.
Method, units and material assumptions ↗