Packaging Film Roll Length, Weight and Purchase Price Checker

Check film roll mass and length together

A supplier may quote by kilogram while another quotes by metre.
A similar-looking roll and a smaller unit-price number do not establish equal usable film or equal purchase cost.
Including the core in film weight, confusing the core bore with its outside diameter, or using the wrong caliper can distort the comparison before price is considered.

This packaging film roll length, weight and purchase price checker puts one web specification and roll quantity on a common basis.
It compares geometric length, length inferred from measured net mass, and agreed billed quantities, then estimates roll counts and effective cost per usable metre.
Small packaging businesses, label printers and production buyers can use the worksheet to identify which measurements and billing assumptions to confirm with a supplier.

What the checker helps you decide

Check that usable length covers the requirement, identify the agreed billing basis, and see whether the conservative scenario needs another roll.
Save the worksheet and confirm caliper, core tare and guaranteed length before placing the order.

Input definitions and units

• Roll OD D and core OD d: both are outside diameters in mm.
  Do not enter the core bore or a radius.
  Check multiple measuring positions on a distorted roll and agree on the measurement method.
  
• Caliper t: the complete thickness in µm that builds up in one wrap.
  1 mm equals 1,000 µm.
  Use total laminate caliper; for lay-flat tubing include every layer stacked in one wrap.
  The calculator does not automatically double tubing values.
  
• Flat web width w: actual wound web width in mm.
  Do not confuse it with finished bag width or a cut piece.
  Width does not change the ideal diameter-derived length, but it changes area and mass.
  
• Material data: enter confirmed density ρ in g/cm³ or complete basis weight s in g/m².
  For coatings, adhesives, foil or voided structures, prefer the supplier-confirmed total basis weight.
  No average density is automatically assigned from a material name.
  
• Gross weight and tare: enter total scale weight G and the included core, caps and packaging weight C in kg.
  Enter both or clear both; blank is not confirmed zero.
  

Field maximums are application arithmetic limits, not acceptable product specifications.
Error fields are absolute ± values.
Roll OD minus its error must still exceed core OD, and caliper minus its error must remain positive.

The diameter-to-length formula

Web width appears in both the wound volume and the unwound film volume, so it cancels from this length equation.
Width is still necessary for area, mass and conversion of kilogram prices.
Half the outside diameter does not imply half the remaining film: the equation uses the difference between squared roll and core diameters.

Cross-check length from net mass

Both length estimates depend on the entered caliper/density or basis weight.
When they disagree, check units, core OD, flat width, total caliper and included packaging first.
Close agreement is not equivalent to independently measuring length on a counter.
The review tolerance is a user decision aid, not a legal shortage tolerance.

Read error scenarios and conservative roll counts

For OD error eD and caliper error et, minimum geometric length uses D−eD with t+et; maximum length uses D+eD with t−et.
In density mode, geometric mass uses the matching scenario caliper, so the caliper change cancels.
It does not multiply minimum length by the nominal mass per metre from a different scenario.
Direct g/m² is fixed, so geometric mass varies with length instead.

With measured mass and density, thicker film implies less length and thinner film more length.
With fixed g/m², mass-derived length does not vary with OD or caliper.
These are scenarios for the entered variables, not confidence intervals; core, density, width and scale uncertainty are omitted.
For production schedules that cannot tolerate shortages, obtain guaranteed usable length and process-specific loss data.

Step-by-step use

1. Choose one product code, width, structure and caliper, then measure roll OD and core outside diameter.
   Do not treat different films as one common roll.
   
2. Confirm full wrap caliper and density or complete basis weight from the specification.
   Include coatings, adhesive and all tubing layers.
   
3. For mass cross-checking, enter measured gross weight with tare and set the OD/caliper errors.
   Without measured mass, select the geometry reference.
   
4. Enter total required usable length and loss on every roll.
   Check continuous-piece requirements and cutting layouts separately.
   
5. Enter each unit price and agreed billing quantity; for kg choose net or gross.
   Align currency and tax/freight scope, then run the check.
   
6. Review mass/length differences, nominal/conservative rolls and usable-metre cost, then save the TXT worksheet.
   Editing clears previous results, so run the check again after changes.
   

Fictional example: five nominal rolls or six conservative rolls

Use OD 300 mm, core OD 90 mm, total caliper 60 µm, width 500 mm, density 0.91 g/cm³, gross weight 30.75 kg and tare 1.5 kg.
Assume OD ±2 mm, caliper ±3 µm, required usable length 5,200 m, loss 20 m per roll and review tolerance 3%.
Ordering uses measured mass; these figures and prices are examples, not product specifications or market prices.

Compare metre, kilogram and per-roll purchase prices

Cost per roll equals unit price multiplied by billed quantity.
An entered agreed quantity takes priority; otherwise the selected length or weight model is used and marked as estimated billing.
Gross-kg billing uses measured gross weight and never silently substitutes net weight.
An agreed gross billing quantity can establish cost even without measured gross mass, but its difference from measured gross remains unconfirmed.

Effective usable-metre cost divides roll cost by length after loss.
Effective net-kilogram cost uses measured net mass when available, otherwise selected-reference estimated net mass.
Budgets multiply roll cost by the corresponding roll count.
Changing KRW, USD or EUR changes the label only; there is no currency or tax conversion.
Blank price means unconfirmed and zero means confirmed free.
Different guarantees, structures or delivery conditions require separate evaluation before choosing a product.

Practical situations and limitations

Coatings, fillers and voids can change density even within the same polymer name.
The tool does not synthesize laminate density or assess food-contact suitability.
For greenhouse cover dimensions, overlaps and cuts, use the separate greenhouse film order planner.

Frequently asked questions