Yes, for a while. An empty, sealed 40 ft dry container weighs about 3,640 kg (8,020 lb) tare and holds roughly 67.6 cubic meters of space inside its steel shell, so it only has to push aside about 3.5 cubic meters of seawater to support its own weight — riding high, with well under 5 inches of an 8-foot-6 sidewall actually in the water. It stops floating once enough water gets past the seams and seals to change that math, and sealed on a shipping container has never meant built for a permanent soak. Figures below are dated 2026-08-30.
Buoyancy math explains both halves: why it floats, and why that doesn't last.
Steel sinks; a sealed steel box does not, because most of what it encloses is air. The table below runs the numbers for a standard 40 ft dry container against seawater at a density of roughly 1,025 kg per cubic meter, the commonly used reference figure for ocean water.
| Figure | Value |
|---|---|
| Tare weight, empty and sealed | 3,640 kg about 8,020 lb |
| Internal capacity | 67.6 m³ 12,032 × 2,350 × 2,390 mm |
| Seawater displaced to float the tare weight alone | about 3.55 m³ roughly 5% of internal capacity |
| Approximate draft, sealed and empty | well under 5 in of an 8 ft 6 in sidewall |
Going the other direction: even counting only the roughly 67.6 cubic meters of load space inside the box, and leaving out the extra volume the steel shell itself adds outside that space, a fully submerged 40-footer displaces about 69,270 kg of seawater. Subtract the container's own 3,640 kg and there is roughly 65,600 kg of buoyant reserve to overcome before it goes under — something has to let in the equivalent of about 64 cubic meters of water, nearly 95 percent of the box's own interior, before the arithmetic flips from floating to sinking.
That reserve of buoyancy is real, but it assumes the box stays sealed, and nothing about a shipping container is built for that assumption to hold indefinitely once it is floating loose rather than standing on a ship. Door gaskets are sized to keep out rain and spray on an open deck, not to hold back a continuous soak. The same two to four wall vents that let a sealed container equalize air pressure on an ocean crossing are, once the box is lying in the water instead of riding on it, a path for that water to trade places with the air still trapped inside — see our page on shipping container vents for what they are actually built to do.
However it happens, a container that goes from riding high and dry on deck to lying in open water is losing its seal a little at a time rather than all at once, which is why a lost container is reported as a hazard for a stretch of time rather than vanishing the moment it hits the water.
“an estimated 1,478 containers were lost at sea in 2025 out of approximately 280 million transported globally” World Shipping Council, Containers Lost at Sea Report: 2026 Update, worldshipping.org, read 2026-08-30
That works out to about 0.0005 percent of everything shipped, up from 576 containers lost in 2024 — and the 2025 total leaned heavily on a single incident, with one vessel loss accounting for roughly 43 percent of the year's count. The same report puts recoveries at 128 containers in 2025, the highest figure recorded since the World Shipping Council began tracking recoveries in 2023 and still under 10 percent of that year's losses. The report also notes a SOLAS amendment now requiring any container lost or observed drifting at sea to be reported, rather than leaving it to whoever spots it first.
Most lost containers, in other words, are never seen again. The most parsimonious explanation is the one the buoyancy arithmetic above supports: they take on enough water to go under, break apart under wave action once they are riding low and unstable, or drift far enough that nobody logs where they ended up. A container awash — mostly submerged, with only a sliver of steel above the surface — is close to invisible at the waterline to both a lookout and a small vessel's radar, and it does not get lighter as it takes on water, which is the reasoning behind reporting it as a hazard rather than an oddity.
The displacement and draft figures on this page are SMKlog's own arithmetic from the carrier-published weight and dimensions above, not a number either source states directly. Loss and recovery totals are annual industry figures and will be superseded by the World Shipping Council's next update.
This site's checkout handles United States domestic parcel labels. An ocean container — loaded, in transit, or being sized up before a move — is priced by a person through freight review, against the actual box, route and cargo rather than typed into this site's calculator.
Yes, at first. An empty, sealed 40 ft dry container weighs about 3,640 kg (8,020 lb) tare and holds roughly 67.6 cubic meters of space inside its steel shell, so it only needs to displace about 3.5 cubic meters of seawater to support that weight — riding high, with a few inches of the sidewall in the water at most. It stops floating once water gets past the seals in enough volume to change that math.
More than most people guess. Even counting only the load space inside the box and leaving out the volume the steel shell itself adds, a fully submerged 40-footer would displace roughly 69,270 kg of seawater against a tare of 3,640 kg — roughly 65,600 kg of buoyant reserve, nearly 95 percent of its own interior volume, has to fill with water before the container actually goes under.
Because neither one is built for continuous immersion. Container doors are gasketed to keep out rain and spray on an open deck, and the two to four wall vents exist to equalize air pressure during the crossing, not to stay dry underwater — see our page on shipping container vents for what they're actually for. Once the box is lying in the water instead of standing on a ship, both become paths for water to trade places with the air still trapped inside.
Most of them. World Shipping Council's 2026 update on containers lost at sea counted 1,478 lost in 2025 against roughly 280 million shipped, and only 128 recovered — the highest recovery count since it started tracking the figure in 2023, and still under 10 percent of that year's losses. The rest sank, broke apart, or drifted somewhere nobody logged them, which is the ordinary way a floating hazard this size stops being found rather than stops existing.
No. This site's checkout prices United States domestic parcel labels, not ocean freight or recovery of a container lost overboard. A container move that needs pricing goes through freight review instead, where a person handles the specifics.