VFFS Bag Size Guide: How to Calculate Film Width, Bag Width and Bag Length

Bag width, film width, and cut length are closely related in a VFFS packaging machine, but they are not interchangeable. A small mistake in one value can cause an undersized pouch, weak seals, wrinkles, excessive film waste, or a film roll that cannot pass through the forming collar.

This guide explains how to estimate the film width and bag dimensions for a standard single-lane pillow pouch, how fin seals and lap seals change the calculation, and when a simplified formula should not be used.

For available liquid, paste, powder, and granule packaging equipment, visit the ZONESUN VFFS Packaging Machine Collection. For other filling and packaging solutions, visit ZONESUNPRO.

What Does a VFFS Machine Do?

VFFS means Vertical Form Fill Seal. The machine unwinds flat roll film, pulls it over a forming collar, wraps it around a forming tube, creates the longitudinal seal, forms the bottom transverse seal, fills the product, and then produces the top seal and cut.

The packaging dimensions are influenced by:

• Finished pouch width
• Finished or usable pouch length
• Longitudinal sealing style
• Longitudinal and transverse seal widths
• Product volume and required headspace
• Bag style, such as pillow, gusseted, stick pack, or four-side seal
• Film thickness, stiffness, friction, and heat-sealing properties
• Registration-mark pitch for printed film
• Machine forming collar and maximum film-roll width

The formulas below are useful for initial estimation. Final film specifications should always be approved by the machine and film suppliers using the actual bag drawing and product samples.

Key VFFS Size Terms

Term	Meaning	Common Mistake
Finished bag width	The left-to-right width of the flat finished pouch	Confusing it with film-roll width
Film width	The total width of the flat roll before it wraps around the forming tube	Ordering film equal to the bag width
Cut length or bag pitch	The film distance advanced for one bag	Confusing total cut length with usable internal length
Usable bag length	The internal product area between the inner edges of the top and bottom seals	Ignoring the space occupied by the seals
Longitudinal seal allowance	The film used to create the vertical back seal	Forgetting that fin and lap seals use different allowances
Transverse seal width	The horizontal sealed band at the top or bottom of the pouch	Adding it incorrectly when the specified bag length already includes the seals

How to Calculate Film Width for a Standard Pillow Bag

A standard pillow bag is formed by wrapping film around a tube and sealing the two longitudinal edges at the back. The basic relationship is the circumference needed for the flat pouch plus the film used for the back seal.

Fin-Seal Film Width Formula

With a fin seal, the two inner film surfaces meet and are sealed together. If each film edge needs a seal allowance of S, the preliminary formula is:

Film width ≈ 2 × finished bag width + 2 × edge seal allowance

Using symbols:

F ≈ 2W + 2S

• F = required film width
• W = target flat finished bag width
• S = seal allowance provided on each film edge

Fin-Seal Example

Suppose the target pouch width is 120 mm and the film supplier or machine design requires 10 mm on each edge for the fin seal:

F = 2 × 120 + 2 × 10 = 260 mm

The preliminary film width is therefore approximately 260 mm.

This is an estimation. The final value can change according to the forming collar, film thickness, required seal appearance, tracking tolerance, and the machine manufacturer’s definition of seal allowance.

Lap-Seal Film Width Formula

With a lap seal, one film edge overlaps the other. If the required overlap is O, the preliminary formula is:

Film width ≈ 2 × finished bag width + overlap allowance

Using symbols:

F ≈ 2W + O

Lap-Seal Example

For a 120 mm finished pouch width and a 15 mm overlap:

F = 2 × 120 + 15 = 255 mm

The estimated film width is approximately 255 mm.

Why Fin-Seal and Lap-Seal Values Are Different

A fin seal uses both film edges to create a projecting sealed fin. The calculation therefore considers the contribution from both edges. A lap seal places one edge over the other, so the calculation is usually expressed as the pouch circumference plus the total overlap.

Do not select the seal style only to save a few millimeters of film. Film structure, product barrier requirements, printable surface, sealant layers, appearance, machine tooling, and seal strength must all be considered.

How to Calculate VFFS Bag Length

Before calculating length, confirm whether “bag length” means:

• Total cut length, including the top and bottom sealed areas; or
• Usable internal length between the seals.

If the customer provides the required usable internal length, the preliminary formula is:

Cut length ≈ usable internal length + top seal width + bottom seal width

Using symbols:

L_cut ≈ L_usable + T + B

• L_cut = total film advance or cut pitch per bag
• L_usable = usable space between the inner edges of the seals
• T = top sealed area
• B = bottom sealed area

Bag-Length Example

If the required usable internal length is 160 mm, the top seal is 10 mm, and the bottom seal is 10 mm:

L_cut = 160 + 10 + 10 = 180 mm

The estimated cut pitch is 180 mm.

If the required finished bag dimension is already specified as 120 × 180 mm and the 180 mm includes the sealed areas, do not add the seals again. In that case, the machine cut length is approximately 180 mm, subject to registration and machine setup.

How Much Headspace Should Be Added?

The bag should not be filled completely to the top seal. Product must remain outside the sealing area, and the package needs enough space for filling variation, product settling, gas displacement, and safe jaw closing.

The required headspace depends on the material:

• Free-flowing granules may settle after dosing.
• Fine powders can become airborne and contaminate the seal.
• Liquids can splash during film movement.
• High-viscosity pastes may leave a product tail near the filling nozzle.
• Fragile products need space to avoid crushing in the sealing jaws.

There is no reliable universal headspace percentage for every VFFS product. It should be determined through filling and sealing tests using the actual product, target weight, film, and machine speed.

Can Fill Volume Be Calculated From Bag Width and Length?

Bag width and length alone do not determine capacity. The forming-tube diameter, pouch expansion, product bulk density, particle shape, trapped air, and required headspace all affect the actual fill volume.

For powders and granules, the same weight can occupy very different volumes. For example, a dense granular material and a fine aerated powder may need different pouch sizes even if their target net weights are identical.

For liquids and pastes, the bag shape changes after filling. A sample bag or three-dimensional volume test is more reliable than multiplying flat width by flat length.

How to Estimate Film Consumption

Once the film width and cut pitch are known, the approximate film area per bag can be calculated:

Film area per bag ≈ film width × cut length

For the 260 mm film-width and 180 mm cut-length example:

0.260 m × 0.180 m = 0.0468 m² per bag

For 10,000 bags:

0.0468 × 10,000 = 468 m²

This theoretical value does not include setup waste, film splicing, registration correction, rejected bags, roll-end loss, or production scrap. Actual purchasing calculations should add an allowance based on the factory’s validated waste rate.

Printed Film and Registration-Mark Pitch

Printed roll film uses an eye mark or registration mark so the machine can cut each package in the correct printed position. The repeat length of the artwork normally needs to correspond to the bag cut pitch.

Before printing a full production roll, confirm:

• Film width
• Artwork repeat or print pitch
• Eye-mark size, color, and position
• Unwind direction
• Which film surface faces outward
• Back-seal position
• Top and bottom seal areas
• Cutting position
• Date-code or batch-code area
• Machine sensor requirements

Printing film before the bag drawing and eye-mark layout are approved can lead to an entire roll that cannot register correctly on the machine.

Do These Formulas Work for Gusseted Bags?

Not without adjustment. A gusset adds film around the sides or bottom of the package. For a simple rectangular tube, a preliminary circumference may consider two front/back panels and two side depths, but the finished flat-bag measurement and gusset definition vary between suppliers.

Gusseted bags also depend on gusset-forming devices, forming-collar geometry, product volume, and the way the finished pouch is measured. Always use a dimensioned bag drawing rather than relying on a single “bag width” value.

Do These Formulas Work for Stick Packs and Multi-Lane Machines?

A multi-lane sachet or stick-pack machine cannot normally be calculated by multiplying a single-lane film width without considering:

• Number of lanes
• Center-to-center lane pitch
• Longitudinal seal widths between lanes
• Outer trim margins
• Slitting-knife positions
• Film tracking allowance
• Printed artwork repeat across the web
• Machine-specific sealing plate layout

The film-width drawing should come from the machine supplier after the lane layout is confirmed. This is especially important for high-speed machines such as the ZS-FS500K4 4-Lane VFFS Sachet Packing Machine.

Bag Styles That Require Machine-Specific Confirmation

Do not apply the standard pillow-bag formula directly to:

• Three-side-seal sachets
• Four-side-seal sachets
• Center-seal gusseted bags
• Quad-seal bags
• Stick packs
• Shaped or irregular sachets
• Chain bags or perforated connected bags
• Hole-punched or header-card bags
• Multi-lane packages
• Packages with a spout or zipper

These formats use different sealing layouts, film paths, or prefabricated components.

How Forming-Tube Size Affects Bag Width

The forming tube and forming collar create the film tube before sealing. A film roll can be mathematically wide enough but still fail to run if it does not match the installed forming set.

Changing to a significantly different bag width commonly requires another forming collar and tube. Smaller adjustments may be possible only within the approved range of the existing components.

When requesting multiple bag sizes, list every width and length. The supplier can then determine:

• Which sizes can share one forming set
• Which sizes require additional formers
• The permitted film-width range
• Expected changeover steps
• Whether the filling nozzle also needs replacement

Common VFFS Size Calculation Mistakes

• Ordering film equal to the desired bag width
• Forgetting the longitudinal seal allowance
• Using a fin-seal formula for a lap-seal package
• Adding top and bottom seals twice
• Confusing usable product space with total cut length
• Estimating capacity only from the flat bag dimensions
• Ignoring powder aeration or granule bulk density
• Printing film before approving the eye-mark layout
• Assuming one forming collar can make every bag width
• Applying a single-lane formula to a multi-lane machine
• Not allowing enough clean area for transverse sealing

Which VFFS Machine Matches Your Product?

Liquid and Paste Sachets

The ZS-FS240L Sachet Filling and Sealing Machine is designed for liquid and paste sachet applications. Bag-size selection should consider splash control, nozzle movement, product viscosity, and clean sealing space.

Powder Sachets

The ZS-FM220 VFFS Powder Sachet Packaging Machine uses an auger filling system. Powder bulk density and dust behavior should be tested when determining pouch capacity and headspace.

Granule Packaging

The ZS-CZP320 Multi-Head Vertical Granule Packaging Machine combines weighing and vertical packaging for granular products. Product piece size, drop height, target weight, and bag volume all influence the forming-tube and pouch selection.

Explore more options in the VFFS Packaging Machine Collection.

Information to Send Before Ordering a VFFS Machine

• Product name and clear photos or videos
• Liquid viscosity, powder bulk density, or granule dimensions
• Target filling weight or volume
• Preferred bag style
• Finished bag width and total cut length
• Required usable internal dimensions
• Top, bottom, and longitudinal seal requirements
• Film material, thickness, and roll specifications
• Printed-film artwork or eye-mark layout
• Required bags per minute
• All bag sizes planned for production
• Options such as date coding, tear notch, hole punch, linked bags, or nitrogen flushing

Frequently Asked Questions

Is film width always twice the bag width?

No. Twice the bag width represents the approximate flat-tube circumference for a standard pillow bag, but the longitudinal seal allowance must also be added. Gussets, multi-lane layouts, and other bag styles require different calculations.

Can I use 240 mm film to make a 120 mm pillow bag?

Normally, 240 mm leaves no additional material for the longitudinal seal. The actual film must include the required fin-seal or lap-seal allowance and must match the forming collar.

Does bag length include the top and bottom seals?

It depends on how the specification is written. Total cut length normally includes the sealed areas. Usable internal length excludes them. Confirm which measurement is being supplied before calculating the machine pitch.

Can one VFFS machine make different bag sizes?

Usually yes within an approved range. Bag length can often be changed through machine settings, while a major width change can require another forming collar and tube. Film, sealing jaws, cutting parts, and filling nozzles may also need adjustment.

Should film be ordered before machine testing?

Only after the supplier confirms the film width, roll size, unwind direction, seal structure, registration mark, and forming set. A short test roll is recommended before printing or purchasing a large production batch.

Conclusion

For a standard single-lane pillow bag, preliminary film width can be estimated from twice the finished bag width plus the correct longitudinal seal allowance. Cut length can be estimated from usable internal length plus the top and bottom seal areas. However, these calculations are only the starting point.

The final film and pouch dimensions must match the forming collar, sealing method, product behavior, filling volume, printed-film repeat, and machine limits. Send ZONESUNPRO your bag drawing, product sample, target weight, film information, and required output before ordering film or selecting a VFFS machine.