Ordering the wrong length is one of the commonest and most expensive mistakes with a new conveyor belt. Too short and it cannot be jointed; too long and the take-up runs out of travel. The calculation is simple once the conveyor is measured correctly.
The formula for an open belt
For a conveyor with a head pulley and a tail pulley:
Belt length = 2 × C + π × (D + d) ÷ 2 + (D − d)² ÷ (4 × C)
where C is the centre distance between the pulleys, D the head pulley diameter and d the tail pulley diameter, all in the same unit. The last term is small and often ignored when the pulleys are similar.
Measuring correctly
- Wind the take-up to its shortest position, or note where it is, before measuring the centres.
- Measure the pulley diameter over the lagging, not the bare shell.
- For a conveyor with snub, bend and take-up pulleys, measure the belt path with a tape along the old belt or add each pulley wrap.
- If an old belt is still fitted, its length is a useful check but belts stretch; do not order from it alone.
Add the splice allowance
A hot vulcanised splice overlaps the two ends in steps, one step per ply less one, plus a bias across the width. The extra length is roughly (plies − 1) × step length + width × tan(bias angle). Mechanical fasteners need no allowance.
Worked example: centres 50 m, both pulleys 500 mm. Open length = 2 × 50 + π × 0.5 = 101.57 m. For a 4 ply belt, 1000 mm wide, with 250 mm steps and a 22° bias, add about 3 × 0.25 + 1.0 × 0.40 = 1.15 m. Order about 102.8 m.
Questions
How do I calculate conveyor belt length?
Belt length = 2 × centre distance + π × (head pulley diameter + tail pulley diameter) ÷ 2, measured with the take-up at its shortest, plus the splice allowance for a hot vulcanised joint.
How much extra length is needed for a splice?
For a stepped hot splice, about one step length for each ply less one, plus the bias across the width: typically 1 to 2 m for common belts.
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