What Is PIW on a Conveyor Belt?
PIW is the most common way US conveyor belts are rated for strength — and one of the most misunderstood. Here's what it means and how to use it.
Working tension vs. breaking strength
PIW is a working tension — the maximum tension the manufacturer says the belt can carry in normal service. It is not the belt's breaking point. If you pull a belt sample until the carcass fails, that higher number is the breaking strength.
The two are linked by a safety factor — the ratio of breaking strength to working tension — which absorbs startup shock and unusual tensions:
| Carcass | Safety factor (breaking : working) |
|---|---|
| Polyester (EP) | 7:1 to 12:1 (traditionally 10:1) |
| Nylon | 10:1 to 18:1 (traditionally 13–15:1) |
Heads-up: some suppliers loosely quote PIW as breaking strength rather than working tension. Always confirm which figure a quote refers to — a "220 PIW" working-tension belt and a "220 PIW" breaking-strength belt are very different products.
PIW and ply count
PIW comes from the belt's carcass — the fabric plies inside it. More plies or a stronger fabric generally means a higher PIW. But ply count alone doesn't fix PIW: two 3-ply belts can carry different PIW ratings depending on the fabric. Specify the PIW you need directly rather than inferring it from plies. The top and bottom rubber covers protect the carcass but add little to the tension rating.
Common PIW ratings
| PIW | ≈ N/mm | Typical use |
|---|---|---|
| 110 | 19 | Light-duty / general handling |
| 150 | 26 | Light to medium duty |
| 220 | 39 | General heavy-duty |
| 330 | 58 | Heavy-duty, higher load |
| 440 | 77 | Heavy-duty, high tension |
| 600 | 105 | Severe / high-tension applications |
Exact rating depends on carcass construction; use this as a guide, not a spec.
PIW → N/mm converter
Cross-referencing a US belt against a metric EP belt? Multiply PIW by 0.1751 to get N/mm.
How to choose the right PIW
Pick a belt whose rated working tension (PIW) exceeds the maximum operating tension of your conveyor, with margin. Maximum belt tension depends on the load, belt length, incline, and pulley diameters; the splice reduces usable strength (splice efficiency), so factor that in too. Size the tension against a CEMA calculation, then match a belt rating above it. Use the conveyor belt calculator for speed and capacity, and send us the conveyor details for tension help.
Frequently asked questions
What does PIW mean on a conveyor belt?
PIW stands for pounds per inch of width. It is the belt's rated maximum safe working tension per inch of belt width. A 220 PIW belt is rated to safely carry 220 pounds of tension for every inch of its width.
Is PIW the working tension or the breaking strength?
PIW is the rated working tension, as defined by NIBA. The belt's breaking strength is higher; the ratio of breaking strength to working tension is the safety factor, traditionally about 10:1 for polyester and 13 to 15:1 for nylon. Some suppliers loosely quote PIW as breaking strength, so confirm which figure a quote refers to.
How does PIW relate to ply count?
PIW comes from the belt's carcass strength, and adding plies or using a stronger fabric raises it. But two belts with the same ply count can have different PIW ratings depending on the fabric, so specify PIW directly rather than assuming it from ply count.
How do you convert PIW to N/mm?
Multiply PIW by 0.1751 to get N/mm. For example, 220 PIW is about 38.5 N/mm. This is useful when cross-referencing US-rated belts against metric EP belts used internationally.
What PIW rating do I need?
Choose a PIW rating whose working tension exceeds the maximum operating tension of your conveyor, with margin. Maximum tension depends on load, belt length, incline, and pulley diameters; splice efficiency also reduces usable strength. Size it against a CEMA tension calculation, and send Jealco your conveyor details for help.
Can Jealco supply a specific PIW conveyor belt?
Yes. As an independent distributor, Jealco sources conveyor belting across many manufacturers in a wide range of PIW ratings, ply counts, cover compounds, and widths. Send your width, length, PIW or ply, compound, and application for a quote.
Sources: NIBA – The Belting Association (working tension definition and safety factors, via Pooley Inc.); standard belt-conveyor engineering practice (CEMA, Belt Conveyors for Bulk Materials ).