Roll Diameter from Weight Calculator
Estimate a roll’s outside diameter from net film weight, width, GSM, thickness and core size. This connects a weight-based order specification with a reel-diameter requirement.
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.
Help with net film weight
Use material weight only. Subtract the core, pallet and outer wrapping from a gross shipment or roll weight. Find the net value on the supplier sheet or weigh it separately.
Help with web width
Measure the full width of the flat material from edge to edge, rather than the width of one finished pack. Choose the matching unit.
Use actual supplier or measured GSM when available.
Help with film gsm
GSM is the weight of one square metre of material, in grams. Find it on the supplier specification; use the complete laminate value for layered film.
Help with film thickness
Use the measured or specified material thickness. One micron (µm) is one thousandth of a millimetre.
Measure the outside of the core, not its bore.
Estimated roll outer diameter
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 = kg × 1,000 ÷ (width × GSM); OD = √(core OD² + 4 × thickness × length ÷ π)
80 × 1,000 ÷ (0.8 × 80) = 1,250 m; √(90² + 4 × 80 × 1,250 ÷ π) = 367.9999381 mmSaved 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.
How sensitive is this result to your assumptions?
Vary one input and inspect estimated roll outer diameter
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 calculator first uses weight, width and GSM to infer running length. It then winds that length mathematically around the stated core using the film’s total thickness. GSM controls how much area the net mass represents; thickness controls the space occupied by that area when wound. These are distinct inputs for a laminate and should describe the same supplied structure.
How to use this calculator
- 01
Enter net film weight, full web width and complete-film GSM.
- 02
Enter total film thickness and core outside diameter.
- 03
Use the estimated finished OD for a preliminary reel specification check.
A calculation you can check
The example checks the approximate outside diameter associated with a specified net roll weight on the selected core.
- Net film weight
- 80 kg
- Web width
- 800 mm
- Film GSM
- 80 g/m²
- Film thickness
- 80 µm
- Core OUTER diameter
- 90 mm
80 × 1,000 ÷ (0.8 × 80) = 1,250 m; √(90² + 4 × 80 × 1,250 ÷ π) = 367.9999381 mmCheck 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 ↗