How to Choose Paper Weight (GSM) for Carrier Bags

What GSM should a paper carrier bag be?

Most machine-made kraft carrier bags use paper between about 70 and 130 gsm: roughly 70-90 gsm for small bags, 80-100 gsm for medium bags and 100-120 gsm or more for large and heavy-duty bags. Premium hand-finished bags use heavier papers, typically 150-250 gsm, mainly for stiffness and print quality rather than load.

GSM (grams per square metre, also called grammage and measured to ISO 536) describes how much paper there is per unit area. It correlates with strength because more fibre means more material to carry stress, but two papers of the same GSM can perform quite differently depending on fibre type, how the paper was made and how the bag was converted.

*Indicative values for virgin kraft with correctly attached handles. Real capacity depends on construction and must be confirmed by load testing production samples.

Why does GSM alone not predict how much a bag can carry?

Because a carrier bag almost never fails in the middle of a panel. It fails where stress concentrates: at the handle patch, the bottom seam or a corner punctured by a hard item. Those points are controlled as much by construction and fibre as by paper weight.

The variables that change load capacity at a given GSM:

• Fibre source. Virgin softwood kraft has long fibres and high tensile and tear strength. Recycled kraft has shorter, repeatedly processed fibres and is typically weaker at the same grammage, so it usually needs a higher GSM to perform equivalently.
• Paper type and stretch. Some kraft grades are made with higher stretch (extensibility), which absorbs shock when a heavy item is dropped into the bag. Two 100 gsm papers with different stretch can behave differently in a drop test.
• Handle attachment. The size of the glued patch, the glue coverage and whether the top is folded over or reinforced decide whether the handle pulls out. A strong paper with a small, poorly glued patch still fails.
• Bottom construction. A block bottom with a full glue pattern, a bottom patch or a base card insert spreads the load; a lightly glued bottom opens under weight.
• Width-to-gusset proportions. A wide bag with a narrow gusset concentrates weight on a small base and puts more strain on the handle patches.
• Moisture. Paper loses strength as it absorbs water. Bags stored in humid conditions, used for chilled products or carried in rain will fail at lower loads than in a dry test.

Where do paper carrier bags fail, and what fixes each failure?

Most failures fall into five patterns, and only some are best solved by increasing GSM. Identifying the failure point on returned bags is the quickest way to choose the right fix.

If returned bags show handle pull-out, a heavier paper will mostly add cost without solving the problem. If they show patch tears or punctures, GSM or fibre is a genuine lever.

How does recycled kraft change the GSM you need?

Recycled kraft usually needs a higher grammage than virgin kraft to carry the same load, often by one step in the supplier's grade range. The exact uplift depends on the recycled grade and the mill, so it should be set by testing rather than assumed.

This matters most in markets that require recycled content. California's SB 1053, for example, requires recycled paper carryout bags supplied at covered stores to contain at least 50 % post-consumer recycled content from 1 January 2028 (the text in force for 2026 and 2027 sets no interim percentage), and New Jersey requires at least 40 %; the rules are summarised in paper bag regulations by market. A chain switching from virgin brown kraft to a compliant recycled grade should re-test its heaviest-load size rather than keep the same GSM by default. The appearance and print differences between grades are covered in brown kraft vs white kraft vs recycled paper for carrier bags.

What is paper bag basis weight in the US, and how does it convert to GSM?

US bag papers are often specified by basis weight in pounds per ream of 3,000 square feet. One pound per 3,000 sq ft equals about 1.63 gsm, so a "50 lb" bag paper is roughly 81 gsm and a "70 lb" paper roughly 114 gsm.

Note that other paper sectors use different ream sizes for basis weight (for example, text and cover papers), so always confirm that a pound figure refers to the 3,000 sq ft bag-paper basis before converting. Quoting both lb and gsm in a transatlantic RFQ prevents misreading.

Do premium hand-finished bags need higher GSM for strength?

Not primarily. Premium bags use 150-250 gsm papers mainly for stiffness, a crisp fold, a smooth print surface and lamination; their load capacity comes largely from the card-reinforced turned top, base card and knotted rope or ribbon handles.

A heavier paper does make the bag stand upright on the counter and keeps sharp edges when displayed, which is part of why it is chosen. But if a hand-finished bag fails, the cause is usually the handle anchoring: holes punched too close to the top edge, a missing or thin reinforcement strip, or knots that slip. The trade-offs of rope, ribbon and paper handles are compared in paper bag handle types.

How should load capacity be tested before approving a bag?

Test production-representative samples with the real product, or an equivalent weight, using a static hang test and a dynamic lift or drop test, and record the result as a pass/fail criterion in the specification. Paper property tests such as tensile and tear support this but do not replace a test on the finished bag.

A practical test plan:

1. Static load: fill the bag with the target weight plus a safety margin agreed with the supplier (for example, the heaviest realistic basket plus a fixed percentage) and hang it by the handles for a set time.
2. Dynamic lift: lift the loaded bag repeatedly from a surface and lower it, simulating customer handling; jerky lifts reveal weak handle glue faster than a static hang.
3. Drop or point load: drop the heaviest hard-cornered item into the bag from a short height to test the base.
4. Conditioning: if bags will be used in humid or chilled settings, test after conditioning samples in comparable humidity.
5. Paper data: request tensile strength (ISO 1924), tear resistance (ISO 1974) and, where moisture matters, Cobb water absorption (ISO 535) from the paper specification, so later batches can be compared against the approved grade.

How samples and batch checks fit into a supply programme is covered in packaging sampling, pre-production approval and quality control.

How to write paper weight into a carrier bag specification

Specify the load the bag must carry and the paper, not just a GSM figure. A specification that says "100 gsm brown kraft" lets a supplier choose any 100 gsm paper; one that states the grade, the fibre basis and the required load produces comparable quotations.

• Target load in kg (and the type of product, e.g. bottles, folded textiles, boxed shoes)
• Paper grade: brown kraft, white kraft, recycled kraft, coated paper
• Fibre basis: virgin or recycled, with any minimum post-consumer recycled content required by law or policy
• GSM, with the US basis weight if relevant
• Handle type and attachment (patch size or "supplier to advise"), top-fold reinforcement
• Bottom construction and whether a base card is required
• Test method and pass criterion for sample approval
• Use conditions: humidity, chilled products, outdoor events

If a supplier proposes a lower GSM than you expected, ask what construction changes support it and request a test result on the proposed spec. Paper weight is one of the main cost drivers in a carrier bag, alongside print coverage and handle type; how these compare across quotations is set out in custom packaging cost drivers. When the specification is ready, the hub on custom printed paper carrier bags lists everything to include in a quotation request, or you can send the brief directly through the contact page.

Related reading

• Paper Carrier Bag Sizes: How to Choose Dimensions and Gusset

US kraft specifications are often given in pounds per ream; the paper weight converter turns them into gsm.