How do I measure the void for a dunnage bag?

Load the container first, then measure the gap at the height where the bag will sit, not at the floor or the top. Measure at the widest point, because a bag sized for the narrow end will be loose at the wide end. If the gap varies along the load, use the widest measurement and check that the bag's height also fits the load height.

What happens if the dunnage bag is too small or too big?

Too small, and the bag cannot bridge the gap: it stays loose, the load can still slide, and the bag may slip out of place in transit. Too big, and the bag is squeezed into a gap narrower than it was made for, which stresses the seams and raises the risk of bursting. Both mistakes waste money — the right size is the one that fills the measured gap snugly at the correct pressure.

What pressure should I inflate a dunnage bag to?

Inflate slowly and keep pressure at or below 0.3 bar, following the bag's own rating. Over-inflation is one of the two costliest mistakes: it does not make the load safer, it stresses the seams and can burst the bag or push cargo out of alignment. Inflate until the bag is firm against both loads, then stop and re-check after a few minutes.

Do I need a dunnage bag, a strap, or both?

Use a dunnage bag when there is a void to fill and the risk is the whole load sliding; use a strap when cargo must be held together as one unit and the risk is toppling or spreading. When the void is large and the load is also top-heavy, use both: strap first to unitise the load, then inflate the bag to fill the void. See our comparison of bags and straps for fragile cargo for the full decision guide.

What Size Dunnage Bag Do I Need? Measure the Void, Then Match the Bag

Q: What size dunnage bag do I need?

Measure the void — the empty gap between two loads, or between a load and the container wall — in centimetres, at the widest point where the bag will sit. Then choose a bag whose inflated width covers that gap without being stretched flat: a bag sized for a much wider gap will be loose, and a bag squeezed into a much narrower gap will be over-stressed. Tezheng's dunnage bags cover voids of about 10 to 50 cm, across six sizes, so match the bag to the measured gap rather than guessing from container size alone.

In short: do not choose by container size — measure the void, the empty gap between two loads (or between a load and the wall), in centimetres, at the widest point where the bag will sit. Then pick a bag sized for that gap: Tezheng's dunnage bags cover voids of about 10 to 50 cm across six sizes. Inflate slowly to no more than 0.3 bar, and re-check after a few minutes. A bag that is too small stays loose and lets the load slide; a bag squeezed into too narrow a gap is over-stressed and risks bursting.

Most dunnage bag failures are sizing failures, not product failures. A shipper orders "the usual size", the gap on this particular load turns out to be different, and the bag either cannot reach across the void or is crushed into a space it was never made for. Sizing takes five minutes with a tape measure, and it is the cheapest insurance on the whole shipment.

Step 1: Measure the void, not the container

A 40 ft container does not tell you the bag size — the gap on this load does. Load the container first, then measure at the height where the bag will actually sit, not at the floor or above the load. Measure at the widest point of the gap: a bag sized for the narrow end will be loose at the wide end, and a loose bag is a bag that slips. If the gap varies along the load — pallets are rarely perfectly square — use the widest measurement, and check that the bag's height also fits the load height so it bears evenly, top to bottom.

Step 2: Match the bag to the measured gap

As a working guide, Tezheng's dunnage bag range is made for voids of about 10 to 50 cm, in six sizes. Within that range, pick the size whose inflated width is close to your measured gap — snug, not stretched flat and not squeezed hard. Two rules of thumb help: if you are between sizes, prefer the size that fills the gap at normal pressure rather than one that needs over-inflation to reach across; and if one gap is much wider than the rest, consider whether the load should be re-braced or a second bag used, rather than forcing one oversized bag to do the whole job. The full step-by-step inflation method is in how to inflate a dunnage bag.

Step 3: Inflate slowly, stop at the right pressure

Inflate slowly and keep pressure at or below 0.3 bar, following the bag's own rating. More pressure does not mean more safety: an over-inflated bag stresses its seams, can burst, and can even push cargo out of alignment. Inflate until the bag is firm against both loads and the load no longer shifts when pushed by hand, then stop. Come back after a few minutes and re-check — cargo settles, and a bag that felt firm at first may need a small top-up. That re-check is the step most often skipped, and the one that catches most problems before the doors close.

Too small, too big, or just right — how to tell

Too small: the bag cannot bridge the gap, stays soft at full inflation, or slips out of place when the load is pushed. The load can still slide, so the bag is decoration, not protection. Too big: the bag is visibly squeezed, its seams are under strain, or it bulges unevenly — it may hold for now and burst on a bumpy road. Just right: the bag fills the gap evenly, sits flat against both loads, feels firm but not drum-tight, and stays put when the load is pushed by hand. If you cannot get to "just right" with one size, tell us the gap measurement — matching a bag to a measured gap is exactly what samples are for.

Bag, strap, or both?

A bag fills voids; a strap holds a unit load together. If the risk is the whole load sliding sideways, a bag is the tool. If the risk is a pallet toppling or spreading, a strap is the tool — see what a cord strap is for how woven strapping works. If both risks are present — a large void and a top-heavy load — use both: strap first to unitise the load, then inflate the bag to fill the void. For the full comparison, see dunnage bags vs foam padding for fragile cargo.

What size dunnage bag do I need?

Measure the void in centimetres at its widest point, then choose a bag sized for that gap. Tezheng's range covers voids of about 10 to 50 cm across six sizes.

How do I measure the void?

Load first, then measure at the height the bag will sit, at the widest point of the gap. Size for the widest point, and check the bag height fits the load height.

What if the bag is too small or too big?

Too small: it stays loose and the load can still slide. Too big: it is squeezed, seams are stressed, and it risks bursting. The right bag fills the gap snugly at the correct pressure.

What pressure should I use?

Inflate slowly to no more than 0.3 bar, following the bag's rating. Stop when the bag is firm against both loads, then re-check after a few minutes.

What is the MOQ and lead time?

Tezheng's export MOQ is 5,000 bags for dunnage bags, with a lead time of about 20 days from production to port. Order samples first and trial the size on a real load before placing a bulk order.

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