Cantilever racking looks simpler than pallet racking, and that is exactly why it gets under-specified. There are no beams to think about, so people size it by total weight and skip the two numbers that actually govern: capacity per arm at a stated load center, and upright spacing set by the deflection of the material rather than by its weight.
The four numbers that define a cantilever system
- Arm capacity, in pounds per arm, at a stated load center
- Arm length, which must cover the depth of the material
- Upright (column) capacity, which is the total of all arms on one side of that column
- Upright spacing, which determines how many arms carry each piece
Get any one of these wrong and the system either fails or, more commonly, quietly deflects until someone notices the material sagging.
Load center is the number everyone misses
An arm rated for 2,000 pounds is rated for 2,000 pounds at a specific load center, normally the midpoint of the arm. Move the load outboard and the effective capacity drops, because you are increasing the moment on the arm-to-column connection.
This matters constantly in practice. If you store 8-foot material on 4-foot arms with the load centered, you are at the rated condition. If you cantilever material out past the arm tip so it overhangs, or if you load a short bundle to the outer half of the arm, you are not.
Always ask the manufacturer for the capacity at your actual load center, not the headline number.
Arm length: cover the depth, then add a little
Arm length should cover the full depth of the stored material, plus a margin. Material overhanging the arm tip concentrates load exactly where the arm has the least capacity, and it is a common cause of both arm damage and dropped loads.
Practical guidance:
- Arms should support the material across at least its full depth
- Add roughly 6 inches of margin for placement error, because a lift truck operator working fast will not center every load
- Where material can roll, specify lip arms or arm stops. Pipe and tube do not stay where you put them.
- Straight arms are for flat stock. Inclined arms hold round stock against the column and are the right choice for pipe.
Upright spacing is set by deflection, not by weight
This is the part that separates a system that works from one that technically holds the load.
The distance between uprights determines the unsupported span of your material. That span, not the total system capacity, controls how much the material sags. Two systems can carry the same total tonnage and behave completely differently.
- Rigid material such as structural steel, heavy bar, and thick plate tolerates wider spacing.
- Flexible material such as thin-wall tube, light bar, extrusions, and long lumber needs closer spacing regardless of weight. Aluminum extrusion is the classic case: light, and it will droop across a span that heavy steel would sit on flat.
- Sheet goods on decking need the deck sized to the sheet, not just the arms.
The working rule: pick spacing so that every piece is carried by at least two arms, and preferably three. For 20-foot bar on 4-foot centers, that is comfortable. For 12-foot material on 8-foot centers, you have two support points and a lot of unsupported end.
Single-sided versus double-sided
Single-sided mounts against a wall, has a shorter base, and takes less floor. It puts all the moment on one side of the column, so it needs either wall bracing or a longer base for stability.
Double-sided stands in open floor with arms both ways. The loads partially counterbalance, so per-column capacity is better used, and the aisle serves two faces.
Base length scales with arm length, because the base is what keeps the column from tipping. A long arm on a short base is unstable even when the arm itself is well within capacity. This is not a place to value-engineer.
Roll-formed versus structural
Roll-formed cantilever uses formed steel columns with arms that adjust on punched holes, usually on close vertical centers. Lighter, less expensive, faster to reconfigure, and right for moderate loads and general storage.
Structural cantilever uses hot-rolled shapes with bolted arms. Heavier, higher capacities, and far more tolerant of lift truck impact. If the system lives in a lane where it will get hit, or if you are into the high per-arm capacities, this is the answer.
Bracing, anchoring, and the floor
Cantilever racking is a tall structure carrying eccentric load. Three things hold it up:
- The base. Sized to the arm length and the load, as above.
- The bracing. Cross-bracing between columns ties the run together. A row of individually braced columns is not the same structure as a properly braced run.
- The anchors. Every column base gets anchored to the slab. Confirm slab thickness and locate any post-tension cabling before drilling.
Rating plaques and inspection
Post the rated capacity per arm and per level where operators can read it. Then inspect on a schedule. Bent arms, deformed connections, and impacted columns lose capacity, and a bent arm is not repaired by straightening it. Damaged components come out of service and get replaced with matching parts from the same manufacturer. Mixing components across manufacturers voids the rated capacity of the system.
What to have ready when you request a quote
- What you are storing: material type, cross section, and whether it rolls
- Length of the longest and shortest pieces
- Weight per piece and weight per arm level you intend to load
- Depth of the bundle or stack on each arm
- Ceiling height available, and any sprinkler or lighting obstructions
- How material is loaded: lift truck, side loader, crane, by hand
- Aisle width available, and whether the system is single or double sided
- Slab thickness and any post-tension
Send us that and we will size arms, columns, bases, and spacing to your material and return a layout with capacities and general drawings. Stamped drawings, seismic calculations, permitting, and installation are available on request as separately quoted services.
