A purchase order that reads “1 tonne bag, 90 × 90 × 110 cm” fixes a volume and a number, not a rating system. One supplier reads 1 tonne as the safe working load. Another reads it as the fill weight the bag usually sees. Most load disputes start here, not in the fabric.
Four numbers that get confused
Term
What it describes
Fill weight
Mass of product put into the bag
Tare weight
Mass of the empty bag
Gross mass
Fill weight plus tare weight
Safe working load (SWL)
Maximum load the bag is designed to carry in service
If a bag is rated 1,000 kg SWL and weighs 3 kg empty, permissible fill is 997 kg. Small, but it is what an auditor asks about. And SWL is a limit for the bag, not a target for the filling line.
Where the safety factor sits
The safety factor (SF) is the ratio between the type-test load and the SWL. A 5:1 bag rated 1,000 kg was tested at 5,000 kg; a 6:1 bag at 6,000 kg.
5:1 — single-trip. Filled once, emptied once; it may be lifted and moved repeatedly while intact.
6:1 — multi-trip, intended for repeated fill and discharge. Standards set no fixed trip count; condition and the user’s risk assessment decide.
Two cautions. The type test qualifies a design, not every bag produced. And SF is not a reserve you can spend — it covers production variation and load distribution, not overfilling.
Why fabric weight does not set the rating
Grams per square metre is one input and a weak predictor on its own. The rating belongs to the assembly: tape strength and weave, seam type and stitch density, how lifting load transfers from loop into body, coating, and UV stabilisation. A heavier fabric with a poorly resolved loop attachment is not a stronger bag in service. Ratings should be quoted against a construction, not a material.
The volume trap
SWL and volume are independent limits, and bulk density decides which binds first.
Low bulk density: 1,000 kg of a light powder may need more volume than the bag has. Capacity is the constraint, not strength.
High bulk density: 1,000 kg of a dense mineral fills only part of the bag, but a full bag would exceed the SWL. The fill level has to be controlled by weight.
Check both: fill weight ÷ bulk density gives the volume the product needs; confirm that volume sits inside usable capacity and the weight sits inside the SWL.
What the rating assumes
A uniformly distributed static load; lifting equipment matched to the loops, all loops engaged; an intact bag; and a bag standing or suspended as designed — not dragged or forklift-pushed. Sharp-edged or hot product, dynamic crane loads and repeated flexing all draw on the same margin the safety factor provides.
Writing it into the order
Fill weight and bulk density.
Required SWL, and single-trip or multi-trip.
Loop configuration and lifting equipment — hook, crane, jib or spreader.
Stacking height and duration, if bags are stored loaded.
The declaration expected: SWL and SF on the bag, on documents, or both.
Ask for the rating against a construction, and reconcile fill, tare and gross mass before the first delivery rather than at the weighbridge.
Hebei Wanhefeng Package Co., Ltd. produces woven PP and PE bulk bags in circular, U-panel and four-panel bodies, with one, two or four loops, sling variants, coated or uncoated fabric and loose, tabbed or form-fit liners. Send the fill weight, bulk density, lifting method and stacking plan, and we will confirm the SWL and safety factor the specification supports before quoting.
Publishing metadata
Suggested category: FIBC Product Insights
Suggested tags: FIBC safe working load, FIBC safety factor, bulk bag load rating, 5:1 FIBC
SEO slug:fibc-safe-working-load
Focus Keywords: FIBC safe working load, FIBC safety factor, 5:1 vs 6:1 bulk bag, 1 tonne bag capacity
Meta Description: What a “1 tonne bag” actually rates: how FIBC safe working load, safety factor, tare and gross mass relate — and why fabric weight alone does not set the limit.
Notes on sourcing and limits
SF practice (5:1 single-trip, 6:1 multi-trip) and the SWL-to-test-load relationship are stated as general industry practice, without citing a specific edition or clause of ISO 21898.
No fabric weights, seam strengths or product load values are quoted; all figures in the text are illustrative arithmetic.
The closing paragraph makes no certification claim and asks for the case to be confirmed before quotation.
About Us
Hebei Wanhefeng Package Co.,Ltd. is a professsional manufacturer of various of container bag, PP fabric, PE fabric, lifting belt, shroud belt and locking line etc. We are near Xibaipo Railway, transportation convenient and quick.We are a private enterprise brand new, registered capital RMB3 million it is a company that focuses on research and development, produce, sale for plastic packing product, including common container bag, Conductive FIBC, Drug FIBC, Food-grade container bag, Drangerous bags, Endometrium bag, Sling bag, Woven bag, inner of container bags and so on. Our company covers an area of 10 thousand square meters, and more than 300 workers, including 20 researchers. The FIBC could be warehouse turnover, recoverable availability, reuse utilization, strong bearing capacity, light weight, easy to mechanical loading and unloading,and facilitate logistics and transportation.
