Free Out of Gauge Cargo Calculator

What is out of gauge cargo?

Out of gauge cargo — or OOG — is any shipment that overflows the internal envelope of a standard 20' or 40' dry container in at least one direction. Length, width, or height. Once a piece of cargo extends past the container walls in any of those axes, it's classified as OOG by the carrier, it gets a different freight class, it needs a different piece of equipment, and it gets a surcharge that can easily double or triple the base rate. This is why people get OOG wrong and regret it at the port.

The practical test is simple. Take a 40' high cube dry container: internally it's about 12,030 mm long by 2,350 mm wide by 2,690 mm tall. Anything that doesn't fit inside that box without bending something is out of gauge. A 13 m long crankshaft is OOG because of length. A 2.6 m wide transformer is OOG because of width. A 3.1 m tall reactor vessel is OOG because of height. The moment any one of those dimensions overflows, you stop booking dry containers and start booking flat racks, open tops, or platforms.

OOG container types: flat rack, open top, platform

Three container types are built for OOG cargo and they solve three different problems. Knowing which one to book is half the battle.

Flat rack containers are the workhorses. They have two collapsible end walls, a reinforced steel deck, and lashing points welded along the side rails. Everything above the deck and everything to the sides is open air. Use flat racks when your cargo overflows the container in width or overall shape — construction equipment, machinery, long sections, yachts. The 20' flat rack has about 5,940 mm of usable deck length and the 40' has about 12,080 mm, with payloads up to 45,000 kg on heavy-duty variants.

Open top containers keep all four walls but replace the roof with a removable tarpaulin. Use open tops when your cargo fits within the internal width of the container but exceeds the standard 2.39 m internal height, and needs to be crane-loaded from above rather than driven in. Common use cases are tall machinery, reactor vessels, pre-cast concrete elements, and anything that can't be tipped through the container door. Open tops give you weather protection on the sides, which matters for cargo that reacts to humidity.

Platform containers are just the deck. No end walls, no lashing rails beyond the corner castings. Use platforms when cargo overflows the container in both length and width — think rail sections, wind tower bases, heavy earth-moving buckets, ship propellers. Platform bookings usually require pre-approval from the carrier and a certified stowage plan, because the cargo effectively takes up four or more container slots on the vessel.

Stow8 supports all three container types. When you start a new plan, you pick which container you're working with and the calculator adjusts its overhang model accordingly. A flat rack calculation is not a platform calculation — the constraints are different and the surcharge math is different.

Overhang dimensions and OOG surcharges

Every OOG shipment has three overhang dimensions, and each one triggers surcharges independently. Longitudinal overhang — front and rear — is the most common, because machinery and pipe sections are often just a bit longer than 12 m. Up to around 500 mm of longitudinal overhang per end is the baseline industry threshold for a light OOG charge. Past 1,000 mm per end you're in the heavy OOG bracket, which typically costs 150 to 300 percent of the base container rate depending on the lane.

Transverse overhang — left and right, measured from the outside face of the container side rail — triggers surcharges much earlier because it directly affects the adjacent container slot on the vessel. Even 150 mm of side overhang on a 40' flat rack can block a neighboring cell and force the carrier to charge you for the blocked slot as well as the OOG fee. Stow8 highlights side overhang as soon as the cargo touches the side rail.

Overhead overhang is the sneaky one. Anything that sticks above the container top rail of a flat rack or open top container consumes vertical cargo space in the vessel's hold stack. The vessel only has so many vertical slots per bay, and an overhead-overhang flat rack makes the slot directly above it unusable. Carriers charge for that blocked slot regardless of whether you asked. If your cargo is more than 2.6 m tall on a standard flat rack, expect an overhead OOG surcharge. Stow8 computes all three overhang dimensions in real time so there are no surprises when the booking request goes out.

Route restrictions: road, rail, and vessel hold

OOG cargo doesn't just need a vessel booking — it needs a vessel booking plus a road leg to the port plus, on many inland origins, a rail leg plus an authorized routing. Each of those has its own envelope, and your cargo has to fit all of them. This is where OOG shipments most often get stuck.

The road leg is typically the tightest constraint. Most trucking jurisdictions allow routine transit up to around 2.55 m wide, 4.3 m tall measured from the pavement, and a total vehicle length around 16 m. Going past any of those thresholds requires a special permit, which can take anywhere from one day to three weeks depending on the country and the specific route. For wider loads, escort vehicles may be required, and for heights above 4.5 m, power line coordination is typically needed.

The rail leg, where one exists, has its own loading gauge profile. Different networks have different envelope shapes, and a cargo piece that clears the European rail gauge may fail the North American one. This is a carrier coordination question, not a calculator question, but Stow8 gives you the exact cargo dimensions you need to quote to the rail operator.

The vessel hold envelope depends on the specific ship class and the slot inside the hold. Most modern container vessels can accommodate up to about 3.1 m of overhead overhang on a flat rack in a deck stack, but hold positions are tighter. If your OOG cargo is going below deck, the overhead overhang budget drops to roughly 800 mm. Stow8 doesn't pick your vessel for you, but the plan export includes the exact overhang numbers you need to hand to the stowage planner.

Regulatory and escort requirements

Many jurisdictions require escort vehicles, time-of-day restrictions, or formal route approvals for OOG cargo on the road leg. The exact rules vary by country and subnational region, and this calculator does not try to replace a local permit expert. What the calculator does is give you the exact finished cargo-on-container dimensions so you can make the permit conversation short. A freight forwarder or permit agent needs to know the out-to-out cargo length, the widest point, the highest point, and the total gross weight. Stow8 surfaces all four numbers in the plan summary and includes them on the PDF export.

How Stow8 helps

• 3D visualization — See your cargo in real space on the container deck before the booking goes out.
• Automatic CoG marker — The green dot shows your load's longitudinal and transverse center of gravity in real time, with carrier-tolerance warnings.
• Overhang callouts — Front, rear, left, right, and overhead overhang are all highlighted and labeled.
• OOG surfacing — Every out-of-gauge condition is listed in the plan summary with the exact trigger dimension.
• PDF export — A one-page loading plan with the 3D view, dimensions, overhang, and CoG — ready to attach to a booking request.
• Multi-container support — If your order needs multiple flat racks or open tops, Stow8 optimizes the distribution across the set.

Common OOG cargo types

• Industrial machinery — CNC mills, injection molding machines, presses, compressors, generators
• Construction and earth-moving equipment — excavators, wheel loaders, asphalt pavers, dump trucks, graders
• Energy infrastructure — transformers, turbines, reactor vessels, pipeline sections, wind tower components
• Pre-fab and modular building components — bathroom pods, curtain walls, structural steel frames, portable buildings
• Long sections — steel beams, pipes, rebar bundles, plate stacks, rail sections
• Yachts and boats — hulls, superyacht tenders, racing sculls, rigid inflatables
• Oversized vehicles — military vehicles, specialized trucks, rail cars

Frequently asked questions

What counts as out of gauge cargo?

Anything that overflows the internal envelope of a standard 20' or 40' dry container in length, width, or height. Practically: anything that overhangs the deck of a flat rack, sticks above the top rail, or is too wide to fit inside a closed container.

When should I use a flat rack vs an open top container?

Use a flat rack when your cargo exceeds the container in width, length, or overall shape but can tolerate weather exposure. Use an open top when cargo fits within the internal width but exceeds the standard 2.39 m internal height and needs to be crane-loaded from above. Flat racks are more flexible; open tops keep the sides protected.

Platform container vs flat rack — which do I need?

A flat rack has two end walls that support the structure. A platform container has no end walls at all. Use a platform when your cargo overflows both the length and the width of a standard container. Use a flat rack when only width or only length overflows. Platforms usually require pre-approval from the carrier and a certified stowage plan.

Does the calculator estimate OOG surcharges?

Stow8 flags the OOG trigger conditions — side overhang past the rail, longitudinal overhang past 500 mm, overhead overhang, weight past the container rating — but it doesn't predict the exact surcharge because every carrier publishes its own tariff. The plan gives you the exact dimensions you need to request quotes from multiple carriers and compare apples to apples.

Can I export a plan to PDF?

Yes. Every plan exports to a one-page PDF with a 3D rendering of the cargo on the container, all overhang dimensions, center of gravity, total weight, and a recommendation line. It's designed to attach directly to a carrier booking request or port operator hand-off.

Do I need to pay?

No. Stow8 is free for the first 15 optimizations per rolling 30-day period. No credit card required. Paid plans start at $18 per month for 100 optimizations; $38 per month for 400 optimizations and advanced features.