Designing a crate for shipping

A crate is designed to protect a machine. The crating supplier quotes and builds it; somebody else pays the freight bill its dimensions go on to create. Those are two different budgets, and in most consignments nobody sits across both.

That split is where the money in this job hides, and this page is about closing it. It comes in two stages, because that is the order the work actually arrives in: first proving that the crates you already build fit the container, and then, once you can see what the container does with them, designing the next crate around the transport rather than around the machine alone.

One boundary first, because it decides whether this page is any use to you. This is about geometry, weight and how many units come out of a container — not about crate engineering. Timber grade, fastener spacing, ISPM-15 treatment and strength class are your discipline and stay yours. Nothing here tells you how strong to build. It tells you what the outside of the finished crate costs to move.

Start with the crate you already build

The first question a crating supplier gets is rarely “what should this crate be”. It is a customer on the phone asking whether six of these fit in a 40-foot container.

That is a good place to start because everything in it is already known. You have a machine, you know roughly how you build the crate around it, and you probably already have the external dimensions from the last one like it. So put those dimensions in as cargo, pick the container, and calculate. You get a count, and — more usefully — you get something to show. Instead of saying you think they should fit, you can put the actual arrangement in front of the customer: the orientation each crate takes, the space left over, and why five go in and six do not.

Three numbers per crate carry most of the weight here — length, width and height as built, not as designed, plus the gross weight including the timber and the skid. The container’s internal envelope is the other half of the sum, and it is smaller than the nominal name suggests; the shipping container dimensions reference has the internal figures and the door apertures, which are a separate constraint from the box itself.

Then look at what is left over rather than at the utilisation figure. The gap between the last crate and the door is not a rounding error. It is the brief for the crate you are still designing.

That last step is the one people miss, and it is worth being blunt about it. What we see with the crating companies we work with is that they come to us to prove the crates they already build fit — and the ones who get the most out of it then use the result to tweak the design. Not on the next job. On this one, while it is still a drawing. The benefit is not the answer at the end; it is being able to see how a design actually sits inside real equipment while you can still change it. Most people arrive not knowing that is available to them, because the question they were asked was “do these fit”, and that question has an answer that sounds final.

So treat the first calculation as the opening of a loop rather than the end of a check. Everything below is what you can change once you are inside it.

What the extra 50 mm costs

The mistake worth naming is not the one you might expect. Crates built dangerously tight to win a quote against a competitor are not the common failure — nobody wants to be the person who said we could have made the crate 50 mm stronger but we wanted to win the job, and they are right not to want that. Timber is cheap relative to a damaged machine, an insurance claim or an unhappy customer, so where there is uncertainty the crate gets built with margin. That is correct behaviour.

The failure is quieter: unnecessary oversizing through a lack of transport awareness. The person designing the crate often does not carry the full consequence of its external dimensions.

Add 100 mm here, reinforce a corner there, use slightly thicker timber, and the crate that looked fine on paper changes the container plan completely. Maybe you go from four machines per container to three. Maybe two crates no longer sit side by side. Maybe the load no longer works through the container door. Maybe you have crossed a dimensional threshold for road transport, and the delivery leg is now a different kind of job entirely.

The same pattern runs through air cargo. Everyone looks at the piece in front of them: the packer thinks about protecting the piece, the forwarder about booking the shipment, the airline about whether it fits the aircraft and whether weight and balance work. Nobody is necessarily responsible for asking what that extra 50 mm cost the whole operation.

The best crating companies ask a different question. Not “how do we protect this machine”, but “what is the smallest safe crate that still works in the actual transport equipment”. Answering that means the load plan has to exist before the crate does.

What the machine actually constrains

Working upstream starts with separating what is genuinely fixed from what you have been treating as fixed.

Fixed: the machine’s real envelope at its widest point, its weight, its centre of gravity, and which faces may be placed downward. Everything else is the crate’s business.

Two of those become explicit settings the moment the machine goes in as cargo. Rotatable says whether the unit may be turned about its vertical axis; tiltable says whether it may be laid on another face at all. A machine that must stay upright is not a geometry problem you can solve by rotating it in the plan, and saying so up front stops the software offering you an arrangement the shop floor would refuse to build. Bottom only and not stackable do the same job for what may be placed above it.

Note what is not on that list: the crate’s own dimensions. Those are an output.

Wall thickness is a dimension, not a detail

This is where internal and external quietly diverge, and where cube goes missing.

Every millimetre of wall, every skid, every clearance you leave between the machine and the inside face of the crate is external dimension, and external dimension is what the container sees. A crate sized outward from the machine plus a habitual margin is right to within a few millimetres on protection and can be wrong by half a container on freight.

The documentation for bundling makes the same point in miniature, about a pallet of juice: the bundled unit is a little larger than the sum of its contents, because the cardboard needs somewhere to be. A crate is that observation at a scale where it costs real money. If you carry a standing allowance — 60 mm of clearance on every face because that is how it has always been done — that allowance is a number worth testing against the container, not a constant.

Where the clearance is genuinely a tolerance rather than a design choice, set it as a margin on the cargo, or globally as an error margin, and keep it out of the dimensions themselves. That way you can see what it is costing you.

One machine per crate, or several

Before sizing anything, decide what goes inside the unit.

Splitting a consignment across crates differently changes the answer, sometimes sharply: parts divided into two crates of unequal size can fill a container better than one crate that is nearly right. This is worth testing rather than assuming, because the winning split is often not the intuitive one, and the test is cheap once the container is in the model. Bundling is the mechanism when several identical items are packed into one shipped unit; for a mixed set of parts, model each candidate crate and compare the counts.

What this page is not deciding is whether the goods should be palletised or floor-loaded at all. That is the shipper’s call, upstream of yours, and a different question.

Modelling the crate: as equipment, or as cargo

A crate can be represented in two ways, and the difference is not a technicality — the two answer different questions. Model it as equipment when the crate is the thing you are designing. Model it as cargo when the crate is already settled and what you need to know is what it does to the shipment.

As equipment: the Container Builder. Use this when the crate matters as a physical structure — the machine goes inside it, it has walls, a floor, a roof and internal construction, and you want to see the relationship between the machine and the crate around it. That is what the builder models: the General tab holds the dimensions and weights and which walls and roof exist, and although the worked example in the documentation is an air pallet, the process is the same for boxes and crates. Once saved, your crate is available in load plans like any other equipment, so you can load the machine into the crate and the crates into the container in the same exercise. It is also the route that lets a closed crate behave as a stackable unit, which working with pallets covers: a “pallet” in this sense may be a closed box, and closed types stack.

As cargo: three external dimensions and a gross weight. This is the first calculation at the top of this page, and for a lot of this work it is all you need. The crate is a transport envelope — the finished package is this big and this heavy, and the question is how many come out of a container and in what arrangement. You are not building the crate in the model; you are pricing its outside.

Cargo can also carry an inner space — a hollow area defined inside the item — where the cavity itself is part of what you are describing. Crates with openings is one of the intended cases, and the hollow container pattern, a cavity set smaller than the outer cargo so that the difference is the wall, reads as a crate cross-section.

If you use it that way, know what the cavity is and is not. It becomes available loading area, so smaller items can be loaded into it, but the crate is not a container by the software’s definition and will not appear in the summaries as one holding other cargo — it appears as another loaded item. If what you hand over is a count of crates and what is inside each one, that difference matters. It is a new feature too: the capability is still growing and we are still discovering how customers put it to work, so tell us what you are trying to do with it.

The short version: designing the crate, build it as equipment. Planning a shipment around a package whose dimensions are already settled, put it in as cargo.

Whether anything goes on top

Headroom above the crate is the other place cube disappears in quantity, and unlike wall thickness it is decided partly by how the crate is built — lid strength and corner posts determine whether a second crate can sit on the first.

Two crates that stack turn a half-used container into a full one; two that do not leave a metre of air under the roof on every unit. So it is worth knowing, before you draw the lid, whether stacking is what the container wants. Set max stacking height and max layers per SKU to reflect what the crate can genuinely take, and max load for the weight one crate may carry on its lid. Allowed overhang decides whether an upper crate has to be fully supported by what is beneath it.

If the honest answer is that nothing may go on top, say so with not stackable rather than leaving it to be discovered in the yard.

Timber against freight

At this point the trade is visible, and it belongs to you rather than to your customer: a marginally more expensive crate that yields a better container fill, or a cheaper crate that ships one fewer unit per box.

Cargo-Planner expresses that trade in a couple of explicit places rather than assuming it. A fixed container cost can be set per container type when you select equipment, so a plan can be pushed toward the cheaper freight bill rather than the fullest vehicle — which matters as soon as the crate is close to a size where a 20-foot container becomes an option. A secondary goal then applies once the container count is settled: minimise used length or height, or improve stability.

What none of this does is invent a crate size. It evaluates the configurations you give it. The value is in the comparison: build two or three candidate crates, run the same consignment through each, and read off the unit count per container. That is a half-hour exercise that can change the quote and, if the crate is a repeat build, every quote after it.

What the shop floor and the customer each receive

One plan, two audiences, and they want different documents.

Fabrication needs the crate as built: outer dimensions, wall build-up, and which face is the lid. The customer needs the shipment — how many crates per container, in what arrangement, and what is left over. Both come out of the same plan as PDF or Excel, and the plan can be shared as a link that a customer or a warehouse opens without an account — which is usually the fastest way to answer the “will six fit” question in writing.

Where to go from here

• The container’s real internal envelope, including the door apertures a crate has to pass through, is in shipping container dimensions.
• If the load plan itself is new to you, what a load plan is and how one gets made covers the concept, and creating a load plan walks the four product steps.
• Once the crate leaves your yard, whether the plan survives the loading bay is a separate discipline — see why loading instructions matter.