PULLEY DIAMETER CALCULATOR
Minimum drum diameters per DIN 22101
Compute the minimum recommended drive, bend, and snub pulley diameters for any standard fabric (EP) or steel-cord (ST) conveyor belt class. Returns a complete 3×3 matrix across DIN 22101 utilization groups so you can see all valid drum sizes for your belt at a glance.
| Drive (A) | Bend (B) | Snub / tail (C) | |
|---|---|---|---|
Group I 60–100 % of rated tension | 1000 mm 39.4 in | 800 mm 31.5 in | 630 mm 24.8 in |
Group II 30–60 % utilization | 800 mm 31.5 in | 640 mm 25.2 in | 504 mm 19.8 in |
Group III Below 30 % utilization | 650 mm 25.6 in | 520 mm 20.5 in | 410 mm 16.1 in |
- D_A = base diameter from belt class table (Drive · Group I)
- Group factor: I = 1.00, II = 0.80, III = 0.65
- Function factor: A = 1.00, B = 0.80, C = 0.63
- D_min = D_A · group_factor · function_factor
Need a verified pulley diameter selection for your conveyor?
Talk to an engineerHow drum diameter selection works
DIN 22101 specifies the minimum drum diameter as a function of the belt's tension class and how heavily it is loaded. A belt running close to its rated breaking strength sees more bending stress on small drums, so the standard mandates larger drums to keep carcass stress below fatigue limits.
Three drum types are distinguished by their function: drive drums (A) carry the full motor torque and see the highest belt tensions; bend drums (B) deflect the belt around the conveyor profile but carry only the static tension; snub drums (C) increase wrap on a drive but see almost no tension. Each step down (A → B → C) allows a smaller minimum diameter.
Three utilization groups (I, II, III) discount the diameter further for belts running below their rated capacity. A 65 % discount (Group III, lightly loaded) is typical for short, low-incline belts that rarely see peak tension. After computing the minimum, round up to the nearest preferred size: 250, 315, 400, 500, 630, 800, 1000, 1250, 1400, 1600, 1800, 2000 mm.
Belt class quick reference
Base drive drum diameter (Group I, drum function A) per DIN 22102 / 22131. The output matrix above derives all other drum types from these base values.
Fabric (EP) belts — DIN 22102
| Belt class | Breaking strength | Base D (Drive A · Group I) |
|---|---|---|
| EP 100/2 | 100 N/mm | 250 mm |
| EP 160/3 | 160 N/mm | 315 mm |
| EP 200/3 | 200 N/mm | 400 mm |
| EP 250/4 | 250 N/mm | 400 mm |
| EP 315/4 | 315 N/mm | 500 mm |
| EP 400/4 | 400 N/mm | 630 mm |
| EP 500/4 | 500 N/mm | 800 mm |
| EP 500/5 | 500 N/mm | 800 mm |
| EP 630/4 | 630 N/mm | 1000 mm |
| EP 630/5 | 630 N/mm | 1000 mm |
| EP 800/5 | 800 N/mm | 1250 mm |
| EP 1000/5 | 1000 N/mm | 1400 mm |
| EP 1250/5 | 1250 N/mm | 1600 mm |
| EP 1600/5 | 1600 N/mm | 2000 mm |
| EP 2000/5 | 2000 N/mm | 2200 mm |
Steel cord (ST) belts — DIN 22131
| Belt class | Breaking strength | Base D (Drive A · Group I) |
|---|---|---|
| ST 500 | 500 N/mm | 630 mm |
| ST 630 | 630 N/mm | 800 mm |
| ST 800 | 800 N/mm | 800 mm |
| ST 1000 | 1000 N/mm | 1000 mm |
| ST 1250 | 1250 N/mm | 1000 mm |
| ST 1600 | 1600 N/mm | 1250 mm |
| ST 2000 | 2000 N/mm | 1250 mm |
| ST 2500 | 2500 N/mm | 1400 mm |
| ST 3150 | 3150 N/mm | 1400 mm |
| ST 4000 | 4000 N/mm | 1600 mm |
| ST 5000 | 5000 N/mm | 1800 mm |
| ST 6300 | 6300 N/mm | 2000 mm |
Common pitfalls
- Picking drum diameter only from the belt class table without checking utilization. A fully loaded EP 1000/5 needs 1400 mm; the same belt at 30 % load only needs ~910 mm.
- Specifying a snub drum at the same diameter as the drive drum. This wastes structural steel and adds inertia at start-up. Use Type C dimensions for the snub.
- Ignoring belt thickness when sizing very small drums for thin / lightly loaded belts. Always check actual carcass + cover thickness against the bending radius.
- Forgetting that the diameter standard refers to the bare drum face. Add the lagging thickness (typically 10–15 mm rubber, 12–15 mm ceramic) when ordering.
- Using DIN values for cold-rated service. Below 0 °C, increase the minimum by one diameter step (or consult the belt maker).
When to consult an engineer
DIN 22101 covers conventional steady-state conveyors. For high-tension belts (ST 5000+), elevated-temperature service, low-temperature service, dynamic start-up loads, or any belt requiring DIN 22101-2 dynamic verification, talk to a BisonConvey engineer for a verified drum specification.
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- 03
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- 08
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