Plastic Film Weight Calculation: Micron to Kg, Roll Length and Pouch Cost

Two film rolls can look almost identical and still give very different packaging costs. One may be 30 micron; the other 35 micron. One may be a flat sheet; the other a tube with two walls. One may have a heavier paper core that makes the gross roll weight look attractive.

For packaging buyers, converters and small manufacturers, the useful number is not just the price per kilogram. It is how much usable film you get for the specification you need.

This guide explains the plastic film weight formula in practical units, with worked examples for LLDPE rolls, blown-film tubes, stretch film and cut pouches. It is written for buyers anywhere in the world, including businesses comparing packaging quotations in Siliguri, North Bengal and across India.

The short answer: plastic film weight formula

For a single-layer, flat film web:

Film weight (kg) = width (mm) × length (m) × thickness (micron) × density (g/cm³) ÷ 1,000,000

For example, a 500 mm-wide, 1,000 m-long, 30 micron film at an assumed density of 0.92 g/cm³ weighs:

500 × 1,000 × 30 × 0.92 ÷ 1,000,000 = 13.8 kg

That is the theoretical net film weight. It excludes the core, wrapping, labels, trim, start-up waste and any film lost during conversion.

Important: The formula assumes the width describes one physical film layer. For an intact blown-film tube measured by its layflat width, there are two walls, so multiply by two.

First, understand the four measurements

1. Thickness: micron or micrometre

A micron (µm) is one-thousandth of a millimetre. A 40 micron film is 0.040 mm thick. A 20 micron film is 0.020 mm thick.

In some markets, suppliers also quote thickness in mils. One mil is 0.001 inch, or 25.4 microns. It is not the same as a millimetre.

When comparing quotations, ask whether the quoted thickness is nominal thickness, average measured thickness or a specified minimum. These are different promises.

2. Width: flat web, layflat tube or unfolded width

A 500 mm flat roll has one 500 mm-wide layer.

A 500 mm layflat blown-film tube has two walls, each 500 mm wide when the tube is flattened. Its total film area per running metre is therefore equivalent to a 1,000 mm-wide single layer.

A centre-folded web and a gusseted bag need their own unfolded-area calculation. Do not assume every product marked '500 mm' has the same film area.

3. Length: metres of usable film

Length is measured along the direction the roll unwinds. A roll's diameter does not tell you its length without more information about thickness, winding and core dimensions.

If you are buying film by weight, length is often the missing quantity. We will calculate it below.

4. Density: the variable many buyers miss

The same dimensions and micron can produce different weights because polymers and blends have different densities.

For the examples in this guide, we use 0.92 g/cm³ as an illustrative polyethylene-film density, not as a universal specification. Real grades vary. For context, Dow lists a density of 0.919 g/cm³ for DOWLEX 2535 PE resin, while other LDPE and LLDPE grades can differ.

A film containing substantial mineral filler may be denser than an unfilled polyethylene film. Do not use 0.92 automatically for filled film, multilayer laminate, BOPP or PET. Ask for the film's measured or agreed density.

Quick conversion table: micron to GSM

GSM means grams per square metre. For a uniform, single film:

Film GSM = thickness (micron) × density (g/cm³)

Using the example density of 0.92 g/cm³:

| Film thickness | Theoretical film GSM |

|---|---:|

| 10 micron | 9.2 g/m² |

| 15 micron | 13.8 g/m² |

| 20 micron | 18.4 g/m² |

| 25 micron | 23.0 g/m² |

| 30 micron | 27.6 g/m² |

| 35 micron | 32.2 g/m² |

| 40 micron | 36.8 g/m² |

| 50 micron | 46.0 g/m² |

| 60 micron | 55.2 g/m² |

This table is useful for quick estimates, but it is not a substitute for a product-specific data sheet. Paper GSM and plastic-film GSM also describe different materials; a 100 GSM paper sheet cannot be compared with a 100 micron film as though the numbers meant the same thing.

Example 1: How much does a 500 mm × 1,000 m LLDPE roll weigh?

Assume a buyer needs:

• Flat film width: 500 mm
• Length: 1,000 m
• Thickness: 30 micron
• Density: 0.92 g/cm³

The result is 13.8 kg net film.

At a hypothetical film price of ₹180/kg, the film-only value is:

13.8 × ₹180 = ₹2,484

That is ₹2.484 per running metre, before conversion, freight, taxes, wastage and any other charges.

Now suppose a second quotation is for the same width and length at 35 micron. The theoretical film weight becomes 16.1 kg. At the same hypothetical rate, its film-only value becomes ₹2,898.

The thicker film costs 16.7% more material than the 30 micron version, because 35 ÷ 30 = 1.1667. That does not mean the thinner film is automatically the better purchase. Seal integrity, puncture resistance, load containment and application suitability still need testing.

Example 2: Flat film versus blown-film tube

This is one of the easiest costing mistakes to make.

Consider a blown-film tube supplied at:

• Layflat width: 300 mm
• Length: 1,000 m
• Wall thickness: 40 micron
• Density: 0.92 g/cm³

First calculate the weight of one wall:

300 × 1,000 × 40 × 0.92 ÷ 1,000,000 = 11.04 kg

Because the tube has two walls:

11.04 × 2 = 22.08 kg net film

If the buyer mistakenly uses the single-layer formula without the second wall, the quotation estimate is only half the actual material requirement.

There is one exception worth checking: if the supplier gives you the total unfolded web width rather than layflat tube width, the area has already been counted. Multiplying by two again would overstate weight.

Example 3: Weight of a 12 × 12 inch tubular pouch blank

A pouch converter may buy a tube and cut it into equal lengths.

Assume:

• Layflat tube width: 12 inches = 0.3048 m
• Cut length: 12 inches = 0.3048 m
• Film wall thickness: 40 micron
• Two film walls
• Density: 0.92 g/cm³

Film area per cut piece:

0.3048 × 0.3048 × 2 = 0.18580608 m²

Film weight per cut piece:

0.18580608 × 40 × 0.92 = 6.84 g approximately

The theoretical material required for 1,000 pieces is about 6.84 kg.

At a hypothetical ₹180/kg, that equals roughly ₹1.23 of film per piece, before sealing, trimming, printing, rejects, labour, power and packing.

If the finished pouch has a bottom seal, cutting loss or another feature, calculate the actual consumed film length, not only the finished external dimensions. A gusset also changes the film area. The weight of the filled product—tea, rice, spices or another material—is separate from the weight of the empty pouch.

For available size examples, see Biolastic's LLDPE pouch range. Actual pouch weight depends on the approved film and converting specification.

Example 4: How many metres are in a 3 kg stretch-film roll?

A roll label may say '3 kg', but does that mean 3 kg of film or 3 kg including the core?

For a reliable length estimate, use net film weight only.

Assume:

• Net film weight: 3,000 g
• Width: 500 mm = 0.5 m
• Thickness: 20 micron
• Density: 0.92 g/cm³

Weight of one running metre:

20 × 0.92 × 0.5 = 9.2 g/m

Theoretical roll length:

3,000 ÷ 9.2 = 326 m approximately

If the 3 kg includes a 400 g core, only 2.6 kg is film. The estimate drops to roughly 283 m.

This difference matters when comparing stretch-film suppliers. Ask for gross roll weight, core weight and net film weight separately.

Stretch performance is another issue. A roll that provides more metres is not necessarily suitable for the same pallet load. Check actual holding force, puncture resistance and wrapping conditions.

Example 5: How to estimate film cost per 1,000 pouches

Suppose the theoretical film weight per pouch is 6.84 g. A production trial shows 5% process loss measured as a share of film input.

To make 1,000 saleable pouches:

• Net film in finished pouches: 6.84 kg
• Required input: 6.84 ÷ 0.95 = 7.20 kg approximately
• Hypothetical film rate: ₹180/kg
• Material input cost: about ₹1,296
• Film-material cost per saleable pouch: about ₹1.30

This distinction matters: adding 5% to finished weight is not exactly the same as dividing by a 95% usable yield.

The total manufactured cost still needs sealing, printing, labour, utilities, maintenance, packing, inspection, freight and any taxes or duties that apply. If a supplier quotes per 1,000 pieces, ask whether those items are included.

Reverse calculation: estimate micron from a known sample weight

You can rearrange the formula.

For a single flat web:

Estimated average micron = weight (g) ÷ [width (m) × length (m) × density (g/cm³)]

For a layflat tube:

Estimated average micron = weight (g) ÷ [2 × layflat width (m) × length (m) × density (g/cm³)]

For example, if a 12 × 12 inch tubular cut piece weighs 6.5 g and density is assumed to be 0.92 g/cm³:

6.5 ÷ (2 × 0.3048 × 0.3048 × 0.92) = about 38 micron

This is an estimate of area-average thickness, not proof that every point is 38 micron. The estimate also depends on the correct density, exact dimensions and whether the sample includes seals, labels or other material.

If the film contains mineral filler, use the actual composite density. Otherwise, the reverse calculation can give a misleading thickness.

Why roll weight and micron measurements sometimes disagree

Before accusing a supplier of under-delivery, check the measurement basis.

The roll may include a core. Core weight should not be counted as usable film.

The material may have a different density. A heavily filled film can weigh more at the same micron. Extra kilograms do not necessarily mean extra film area.

The width may be described differently. Layflat width, unfolded width and usable slit width are not interchangeable.

The film may have gauge variation. Thickness can change across the width or along the roll. A single sample cannot describe every part of a production batch.

The sample may not be dry or clean. Dust, labels, moisture or extra packaging can affect a small weight measurement.

The quoted micron may be nominal. Agree on measurement location, tolerance and acceptance criteria before ordering.

For technical testing, ASTM D6988-26 is a guide for determining thickness of plastic film test specimens. Its scope is not a ready-made commercial sampling plan for an entire shipment. Buyers should separately agree on a practical inspection method and tolerance.

How to check a film delivery without expensive equipment

For a first-level incoming inspection, a small manufacturer can build a useful routine:

1. Record the product name, batch or lot number, resin or film type, nominal micron and width.

2. Weigh the full roll, then deduct the known core and packing weight to obtain net film weight.

3. Measure actual film width and take a measured-length sample.

4. Weigh that sample on a suitable calibrated balance.

5. Estimate average micron using the correct area and density.

6. Measure thickness at several positions using an appropriate calibrated gauge.

7. Run a practical trial on the intended sealing, wrapping or converting machine.

8. Record any tears, leaks, weak seals, blocking, wrinkles or unexpected waste.

A theoretical weight check is valuable, but it cannot replace a machine trial. A film that looks economical on a spreadsheet can become expensive if it repeatedly fails on the packing line.

Flat rolls, tubes, gussets and laminates: what changes?

| Product form | Area rule for the calculation | Important caution |

|---|---|---|

| Flat single web | Width × length | Count one layer |

| Intact layflat tube | 2 × layflat width × length | Count both walls |

| Centre-folded film | Count the actual unfolded film area | Clarify whether quoted width is folded or open |

| Gusseted tube or bag | Sum all developed panel and gusset areas | Use the actual converted shape |

| Multilayer laminate | Add each layer's thickness × density × area | Include adhesives and coatings where material |

For multilayer packaging, one generic density can hide meaningful differences. A more accurate calculation adds the mass of each layer using its own thickness and density, then includes adhesive or coating mass where relevant.

For irregular pouches, handles, holes or shaped seals, use a cutting pattern or verified consumption per piece rather than assuming a simple rectangle.

Price per kg versus price per usable square metre

Price per kilogram is convenient for purchasing, but it does not tell the whole story.

For flat film:

Usable area (m²/kg) = 1,000 ÷ [micron × density (g/cm³)]

At 30 micron and 0.92 density:

1,000 ÷ (30 × 0.92) = about 36.23 m²/kg

At 40 micron and the same density:

1,000 ÷ (40 × 0.92) = about 27.17 m²/kg

The thinner film gives more square metres per kilogram. Whether that is beneficial depends on whether it still passes the required performance tests.

A useful commercial comparison is:

Delivered cost per 1,000 saleable packs = total delivered material and converting cost ÷ saleable packs × 1,000

This is usually more meaningful than comparing two unrelated prices per kilogram.

What should international buyers put in a film RFQ?

Buyers in India and overseas can avoid several rounds of clarification by sending a specification-led request.

Include the polymer or laminate structure, whether the film is flat or tubular, nominal and acceptable thickness, width, length or net weight, core dimensions, required colour or print, use case, sealing or wrapping method, expected order volume and delivery destination.

Also request the agreed tolerance, sample approval process, packing configuration, test reports relevant to the application, production lead time and quote validity.

For cross-border purchasing, ask separately whether export supply is offered for the destination, which Incoterm is quoted, and which shipping and regulatory documents can be provided. Do not assume that a domestic supply listing means a supplier already supports every export market.

A note for buyers in Siliguri and North Bengal

Businesses in Siliguri, Jalpaiguri, the Dooars and nearby North Bengal markets may use film for tea, spices, groceries, dry-food pouches, carton bundling and pallet wrapping.

For these applications, the first step is not choosing the lowest quoted micron. Bring a sample of the product to be packed, the pouch or roll dimensions, expected monthly volume and the machine's sealing or wrapping requirements.

Biolastic, based in Siliguri, lists LLDPE pouches and industrial film products in its catalogue. Buyers should confirm the currently available specifications, quantities and delivery arrangements when requesting a quotation.

Frequently asked questions

How do I calculate the weight of a plastic film roll?

For a single flat web, net film weight in kg = width (mm) × length (m) × thickness (micron) × density (g/cm³) ÷ 1,000,000. Use actual film density and exclude the core, packaging and waste.

How many grams per square metre is 40 micron LLDPE film?

At an assumed film density of 0.92 g/cm³, 40 micron film weighs 36.8 g/m². This changes with resin grade, fillers and additives, so use the measured film density for accurate costing.

Does a tubular blown-film roll weigh twice as much as a flat film roll?

At the same layflat width, length, wall thickness and density, an intact tube has two film walls and about twice the film weight. Do not double the width if the supplied figure is already the total unfolded web width.

How much does a 12 x 12 inch LLDPE tube weigh at 40 micron?

Assuming 12 inches layflat width, 12 inches cut length, two walls and density 0.92 g/cm³, the theoretical film weight is about 6.84 grams per cut piece, before sealing, trimming or scrap.

How do I estimate metres in a stretch film roll from its weight?

Divide net film weight in grams by thickness (micron) × density (g/cm³) × width (metres). For 3 kg net film at 20 micron, 500 mm width and density 0.92, theoretical length is about 326 metres.

Can film weight prove that the supplier delivered the correct micron?

Weight estimates average thickness when film area and density are known, but cannot reveal local gauge variation or verify sealing and mechanical performance. Measure thickness at multiple positions and agree on an inspection method.

Final takeaway

A few measurements can make a packaging quotation much easier to judge: film width, length, micron, density and net film weight. For tubes, count both walls. For filled or multilayer materials, use the correct material densities. For finished pouches, include actual cutting and converting loss.

Most importantly, check the film on the machine where it will be used. The best-value roll is the one that delivers the required performance at a predictable cost per usable pack.

If you are comparing LLDPE pouch or packaging-film specifications, contact Biolastic with the size, thickness, material, quantity and destination to request a specification-based quotation.