Use the reel information you can verify
Roll length, web width and measured GSM describe the amount of film on a reel. Gross reel weight describes film plus its core and any additional tare included in the measurement. Mixing the two overstates the amount of material and understates a price per net kilogram.
Record the width in metres, length in metres and GSM in grams per square metre. Area = width × length. Net film mass in kilograms = area × GSM ÷ 1,000. A 0.8 m wide reel with 5,000 m of film at 60 GSM contains 4,000 m² and 240 kg of net film.
Reconcile dimensions with a scale measurement
If the same reel weighs 248 kg on a scale and its measured core and other included tare total 8 kg, net material weight is 240 kg. This agrees with the dimensional estimate. If the numbers disagree substantially, check nominal length, actual width, GSM sampling and what the scale measurement includes.
Do not subtract an assumed core weight just because another reel uses a similar core. Core dimensions, material and moisture can differ. If tare is unknown, label the weight as gross and keep the resulting material-cost estimate provisional.
Value the net contents
At €768 per reel, the example reel costs €3.20/kg of film, €0.192/m² or €0.1536 per running metre. Using the 248 kg gross weight would give approximately €3.097/kg, creating an apparent discount that comes from counting the core as film.
If the reel contains damaged or unusable material, distinguish nominal contents from useful output. For an illustrative usable-area loss of 2%, useful area is 3,920 m² and the cost is approximately €0.1959 per useful square metre. This adjustment should come from your process data rather than an arbitrary universal waste percentage.
Treat diameter-based estimates as estimates
Where no length is available, roll geometry can support an estimate using outer diameter, core outer diameter and material thickness. In an ideal tightly wound cross-section, length is proportional to the difference between the squared diameters and inversely proportional to thickness.
Real reels can include entrained air, compression, nonuniform thickness and loose winding. Core inner diameter is also not the winding diameter. Use diameter estimates for planning and cross-check them against measured reel data before relying on them for a purchasing claim or guaranteed production quantity.
Common questions
Does roll weight include the core?
Gross roll weight does; net film weight does not. Confirm how the supplier labels the figure before normalizing a price.
Can reel dimensions guarantee production output?
No. They describe nominal material quantity. Useful output also depends on losses, defects and the converting process.