How to choose a big bag: what to look for
A big bag is chosen by five parameters: safe working load (SWL) for the cargo weight, volume for its bulk density, number of loops for the lifting method, safety factor 5:1 or 6:1 for the number of trips, and top and bottom design for filling and discharge. For moisture-sensitive and food cargo, a polyethylene liner is added.
Load rating and volume: from cargo weight and density
Big bags are made for 500–3000 kg; the most common is a 90×90×130 cm bag rated 1000 kg with a volume of ~1.05 m³. Heavy cargo (sand, crushed stone, cement) hits the load rating first: the bag is filled partly but carries a tonne. Light cargo (grain, pellets, sawdust) hits the volume first: such a bag holds only ~780 kg of wheat, so a full tonne needs a 95×95×150 cm bag.
All standard models are listed in big bag sizes: table and selection, and the number of bags for a batch is worked out by the calculator: how many big bags you need per N tonnes.
Design: 2 or 4 loops
2-loop
Two loops — for loads up to 1000 kg lifted by a crane hook or forklift tines through both loops. Cheaper and more compact, but less stable when stacked.
4-loop
Four loops — up to 3000 kg. The body keeps its shape and a forklift can pick the bag from any side; required for heavy cargo and stacking.
More on the 2-loop big bags and 4-loop big bags pages. How to lift a bag by forklift or crane and how many tiers you can stack is covered in safe big bag handling.
Top and bottom: how you fill and discharge
- ✔Open top — the simplest option for filling from a bucket or grab.
- ✔Filling spout on top — for dust-free filling from a hopper or pipe.
- ✔Top skirt — for outdoor storage: it covers the contents against rain.
- ✔Flat bottom — for storage and discharge by tipping.
- ✔Discharge spout at the bottom — for feeding a line, conveyor or elevator without cutting the bag.
Bags with a bottom spout are in the big bags with discharge spout section.
Safety factor: 5:1 or 6:1
SF 5:1 is a single-trip bag: in a destructive test it withstands five times its SWL and is designed for one transport cycle. SF 6:1 is multi-trip, good for 2–3 cycles as long as the fabric and loops are intact; it costs 10–20% more but pays off when reused. What these figures on the label mean and which tests stand behind them is covered in the article on the ISO 21898 standard.
Liner: protection from moisture and dust
A 60–150 µm polyethylene liner is needed for hygroscopic cargo (grain, sugar, flour, cement), for outdoor storage and for food — food and seed go only into new big bags with a liner. For dry cargo in a closed warehouse a liner is optional. Options are in the big bags with liner section.
What to check with a supplier
- ✔Label marking: SWL, safety factor, manufacturer, production date. A missing SWL or SF is a warning sign.
- ✔ISO 21898 design test reports — reliable manufacturers provide them on request.
- ✔Whether the supplier makes bags to your dimensions and from what minimum batch.
- ✔Shipping lead times at the peak of the season.
How each parameter affects the cost is explained in what determines the price of a big bag.
Checklist: 6 questions before ordering
- What is the cargo and its bulk density? It sets the bag volume.
- What is the batch weight? It sets the number of bags.
- What lifts the bags — a crane or a forklift — and will they be stacked?
- How many times will the bags be used: one trip or 2–3?
- How will you fill and discharge: from a hopper, onto a line, by tipping?
- Is the cargo sensitive to moisture, and will the bags stand indoors or outside?
The answers are all the information needed to pick a model and quote a price. Buy big bags wholesale from the manufacturer UkrBagPak from 50 pieces: standard sizes ship from the Zhytomyr warehouse within 1 business day, custom sizes are made to the customer's drawings.