Why is the warehouse full when there is room above?
Because the forklift sets the limits.
It needs wide aisles to turn and has a height ceiling, so the floor goes to traffic and the volume above stays empty. An automated crane works in a narrow aisle and rises as high as the structure goes.
What it is
It is a crane that lives inside the aisle: it runs on a floor rail, guided by another at the top, and raises its forks to the position. Since it does not turn, the aisle is barely wider than the load.
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The system is completed by the racking, the in-feed and out-feed conveyors and the software that decides which pallet goes to each slot.
In practice
A crane, called a stacker crane, travels inside the aisle between two racks, rises to the slot and places or retrieves the full pallet, with no people inside. It solves at once the height a forklift cannot reach and the wide aisle it needs.
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It is assessed after layout and racking, when volume and building height justify it.
What is a pallet stacker crane?
From 7 to 40 metres: the band where the system makes sense
Automated pallet systems work between 7 and 40 metres of storage height. Below that band, racking with a good forklift is almost always the better answer, because the jump in investment finds no volume to pay itself back.
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Inside the band, the gain comes from two directions at once. On height, the densification factor we use as a design reference reaches up to 3 times against conventional selective racking, and that is the ceiling: going higher does not multiply further, because from there the limit is set by something else. On aisles, the machine never turns, so the aisle is dimensioned barely wider than the load and floor that today goes into circulation becomes storage positions instead. Put together, freed floor space reaches up to 66%. Both figures are STOKA design criteria and are recalculated on your own warehouse during the survey.
Cold store: where the arithmetic closes fastest
Stacker cranes work down to −30 °C, so the freezer chamber is home ground. It is also the application where they justify themselves soonest, because the refrigerated cubic metre is the most expensive one in the warehouse: you pay for the floor, you pay for the insulation and you pay for the energy that keeps it cold around the clock.
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As a reference for what the square metre costs before you even chill it, premium industrial rent in Greater Buenos Aires stands at USD 7.33 per square metre per month, and USD 14.52 in the City of Buenos Aires (CBRE, second quarter of 2026). Every square metre you do not need to chill is that figure times twelve, plus energy. On top of that there is what never reaches the spreadsheet: nobody spends the shift inside the chamber, so the cold breaks, the thermal clothing and the staff turnover that every freezer operation knows simply disappear.
What the building has to meet
Three things are measured before anything is drawn. Real clear height, which is not the roof but the lowest interfering point: the underside of a beam, a sprinkler pipe, a cable tray, a light fitting.
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That is what tells you how many levels actually fit. The floor, which has to meet a given flatness and a given permissible load: the stacker crane runs on a rail and works tens of metres up, so an unevenness a forklift would never notice is amplified at the top. The required values are set by the equipment manufacturer according to the system chosen; we measure them on site during the survey and tell you whether the floor complies or what work is needed. And the building itself: columns, doors, loading bays and where goods come in and go out, because the system is not only the crane but also the conveyors that feed it.
The load unit is what rules
The system does not handle goods: it handles load units. It needs a standard pallet, with dimensions and weight inside a narrow range, in good condition and properly stacked.
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A pallet with a broken board, loose film or a carton hanging over the edge is what stops an automated installation, not height or speed. That is why every project includes a profile check at the entry point: a station that verifies dimensions, weight and stability before the pallet enters the aisle, and rejects whatever fails. If you work today with four different pallet sizes and goods that overhang, there is a piece of work to do first, standardising the load unit, and it is worth doing whether you automate or not. When it is the small load unit that is not standardised, the conversation is a different one: there the equivalent for cartons, trays and totes is the miniload.
What is a stacker crane, and what is an AS/RS?
An AS/RS (automated storage and retrieval system) is a storage system in which machines guided by software store and retrieve loads without a driver for each move.
The stacker crane is its best-known machine: a crane that runs on a floor rail inside the racking aisle, guided by an upper rail, with a mast, a carriage that rises along it and a load-handling device that reaches into the rack. A unit-load stacker crane moves full pallets; a miniload crane moves totes, trays and cases. The cycle is always the same: the WMS issues the order, the control system assigns the crane, travel and lift happen at the same time, the load is stored or retrieved, and the move is confirmed in real time.
Stacker crane advantages and disadvantages
What it gains: it uses the height a driven forklift cannot reach, within the 7 to 40 metre band where these systems work, with density up to three times that of conventional selective racking; it enforces first-in, first-out rotation without anyone managing it; it records every move as it happens; and it takes people out of the aisle.
It works in freezer rooms down to −30 °C. What it costs: it is a capital investment, the building must meet the checks done before design, changing the layout later is far more expensive than moving racking, and it depends on software integration. Load capacity is not a single figure: it is stated in the datasheet of the chosen crane and checked against your real load unit.
What decides whether a pallet stacker crane is the answer?
We do not publish model-by-model specification tables: the detailed sheet comes with the assessment, sized against your operation. These are the criteria the choice is made on.
Real clear height, measured to the lowest point
It is measured to the underside of the beam or to whatever interferes, never to the roof. Below 7 metres a pallet system like this one does not fit, and the option to look at is vertical tower storage. Between 7 and 40 metres the system comes into play and the densification factor reaches its 3x ceiling.
Volume per SKU and movement profile
The system pays off with intensive, repetitive and predictable movement of full pallets. Many stock keeping units (SKUs) with very little volume each, or sporadic goods in and out, leave the investment idle for most of the day.
A standardised load unit
One standard pallet, with dimensions, weight and condition inside range. If the goods are too uneven to define that unit, you standardise first and automate afterwards; the other way round has never worked in any warehouse.
Floor: flatness and permissible load
The stacker crane rail demands tolerances an ordinary warehouse floor may not meet. The values are set by the equipment manufacturer according to the system chosen and are verified on site, with instruments, during the survey.
How stable the layout will stay
An automated system is fixed structure: the racking is part of the machine. If the operation is going to move, change sector or redesign its layout within a few years, flexibility is worth more than density.
When is a pallet stacker crane the wrong answer?
It does not pay with loads so uneven that no standard pallet can be defined, because the system would spend the day rejecting entries.
Nor with few positions: the investment has a floor and the cost per position soars. Nor if the operation is about to change, because a fixed structure ties it down; racking is better then. And if the inventory does not reconcile, process comes first: automating speeds up the disorder.
Frequently asked questions
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Tell us about your case01What is a stacker crane?
A stacker crane is an automated crane that travels inside a racking aisle on floor and top rails and stores or retrieves loads at any position, with no operator on board. It is the core machine of an AS/RS for pallets (unit-load) or for totes and cases (miniload).
02What does AS/RS mean?
Automated storage and retrieval system: racking, machines that store and retrieve loads, in-feed and out-feed conveyors and control software working as one system. AS/RS and ASRS are the same term written two ways.
03How many pallets an hour does the system move?
We do not publish cycles per hour or performance tables, and that is deliberate. Real throughput depends on height, aisle length, number of machines, order sequence and how loads enter and leave. That figure is calculated on your own operation and delivered, already dimensioned, in the technical sheet of the diagnosis.
04Does it work in a freezer chamber?
Yes. Stacker cranes work down to −30 °C and it is one of the applications where they justify themselves soonest, because the refrigerated cubic metre is the most expensive one in the warehouse and because nobody has to spend the shift inside it. The chamber and the insulation are designed together with the system from the start, not afterwards.
05Can I install it on the floor I already have?
It is verified, not assumed. Flatness, the condition of the joints and permissible load in kilos per square metre all matter. The required values are set by the equipment manufacturer according to the system chosen and are measured on site during the survey, before quoting. If the floor does not comply, the work is sized and becomes part of the project.
06How long from signing to running?
Installation takes 3 to 4 months from the purchase order, and the detailed engineering comes before that. The payback we use as a design reference sits between 18 and 36 months, and it is indicative: it is recalculated with your own figures for floor space, headcount and movement during the diagnosis.
Before automating,measure the warehouse
The on-site survey establishes real clear height, floor flatness and load, load unit and movement profile. With that we deliver layout, technical sheet and quotation. And if racking is enough for you, we will say so.