How to Select a Gravity Roller for a Roller Conveyor
The load a gravity roller actually carries is not the weight of the package. It is the weight divided by the rollers in contact, multiplied by how hard the package arrives.
Start With What the Roller Really Carries
A roller conveyor never carries a package on every roller. How many rollers share the load depends on the base of the conveyed product, and that is where selection starts.
Where the base is hard and does not deform — steel, rigid plastic, a stiff pallet — the load is shared by roughly two rollers at any moment. The loading weight for one roller is the weight of one conveyed product divided by two.
Where the base is flexible — a soft carton, a sack, a bag on a tray — the base sags between rollers and more rollers carry it. The loading weight for one roller is the weight of one conveyed product divided by the number of rollers in contact minus one.
Then Multiply by the Impact Coefficient
Packages are rarely placed gently. The coefficient N below is applied to the per-roller weight to give the load the roller has to survive.
| Loading impact force | Example | Coefficient N |
|---|---|---|
| Not present | Only the conveyed product | 1 |
| A little | Loaded slowly by hand | 1.5 |
| A little strong | Loaded by forklift | 1.5 to 2 |
| Strong | Hoist or crane | 2 to 3 |
| Strong | Loading from a person's shoulder | 3 |
If the impact is spread evenly over four or more rollers, multiply the per-roller loading weight by N. If the impact lands on a single roller — a corner dropped first, a long part swung down at one end — multiply the whole conveyed product weight by N and size that roller for it.
Double Track Conveyors Carry More
On a double track roller conveyor, more rollers support the load at once, so the same conveyor can carry roughly 1.5 to 1.8 times the normal weight. This is the usual arrangement for pallet handling, where the pallet runners sit over two roller tracks.
The Rule to Check at the End
One roller's rated strength must be greater than or equal to one roller's loading weight multiplied by the coefficient N. If that inequality fails, the options are a stronger roller, more rollers under the load through a closer pitch, or removing the impact by changing how the product is loaded.
Where Rollers Fail Instead
Two failures have nothing to do with load rating. The first is the bearing end cap: the wrong press fit for the tube, or a plastic housing in a heavy or hot application, and the roller drags long before the tube is stressed. The second is the shaft form: a spring-loaded round shaft in a frame that vibrates will eventually walk out of its slot, which is what hex shafts exist to prevent.
Components referenced in this guide
Frequently Asked Questions
Does the pitch of the rollers matter as much as the rating?
Yes. Pitch decides how many rollers share the load, and it must be close enough that at least three rollers are under the shortest package at all times.
What coefficient should I use for forklift loading?
Between 1.5 and 2, according to the loading table used for gravity roller selection. Hoist or crane loading goes to between 2 and 3.
Still not sure which model fits?
Send the load, dimensions and environment and we will point to the right family.