Conveyor Idler Spacing Calculator

The raw sag formula, Si = (8 × T × sag%) / (W × g), is clamped to a practical 0.6–2.0 m range before it's reported, since real installations don't use spacings outside that band regardless of what the math produces. If your inputs push the raw calculated spacing above 2.0 m or below 0.6 m, the clamp is what you're seeing — try a lower belt tension or tighter sag limit to see the formula's unclamped sensitivity, or check the actual-sag-percent output to see how far off the clamped spacing is from your intended sag limit.

Return idlers only support the empty belt on its way back to the tail pulley, with no material load, so they can be spaced much farther apart without excessive sag. The calculator sets return spacing at 2.5 times the carrying spacing, capped at 3 m, reflecting that the combined load per meter driving the sag formula (material plus belt weight) drops to just the belt's own weight on the return strand.

Impact idlers sit directly under the loading point, where falling material delivers a concentrated shock load rather than the steady distributed load the rest of the belt sees. The calculator spaces them at half the carrying-idler distance across an impact zone sized to twice the belt width, giving denser support exactly where the belt takes the heaviest hits.

A low tension drives the sag formula's numerator down relative to your load, pushing the raw carrying spacing toward (or past) the 0.6 m floor — meaning you'd need idlers packed unrealistically close together to keep sag in check. In practice this signals the belt tension is undersized for the throughput and belt width you've entered; running a belt tension calculation first, as the tool assumes, will catch this before it shows up here as a maxed-out idler count.

Your sag limit (2% typical, up to 5% in this tool) is the target used to solve for spacing, but because that spacing gets clamped to the practical 0.6–2.0 m range, the sag you'd actually get at the clamped spacing can differ from your target. The calculator back-calculates this as actualSagPercent by plugging the clamped spacing back into the sag relationship, so you can see whether the real installation will run tighter or looser than the limit you specified.