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 is what it means, how it relates to breaking strength and ply count, and how to convert it to metric.
Pounds per inch of width
A belt's rated working tension for each inch of its width.
Working, not breaking
Breaking strength is higher, by the safety factor.
1 PIW = 0.1751 N/mm
For cross-referencing metric EP belts.
Specify PIW, not plies
Same ply count can mean different ratings.
The short answer
PIW stands for pounds per inch of width: a conveyor belt's rated maximum safe working tension per inch of belt width. A 220 PIW belt is rated to safely carry 220 lb of tension for every inch of its width, so a 24" wide 220 PIW belt is rated for 24 × 220 = 5,280 lb of working tension. (Definition per NIBA, the belting association.)
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. Pull a belt sample until the carcass fails and you get the higher number, 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) |
Watch for this in quotes: some suppliers loosely quote PIW as breaking strength rather than working tension. A “220 PIW” working-tension belt and a “220 PIW” breaking-strength belt are very different products, so always confirm which figure a quote means.
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 does not fix PIW: two 3-ply belts can carry different 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 from wear, cuts and heat, but add little to the tension rating.
Common PIW ratings
Typical ratings and where they are used.
| 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 |
The exact rating depends on carcass construction; use this as a guide, not a spec.
PIW to N/mm converter
Cross-referencing a US belt against a metric EP belt? Type in either box.
1 PIW = 0.1751 N/mm (1 lbf = 4.4482 N; 1 in = 25.4 mm).
How to choose the right PIW
Pick a belt whose rated working tension exceeds the maximum operating tension of your conveyor, with margin.
1. Work out the tension
Maximum belt tension depends on the load, belt length, incline and pulley diameters. Size it with a CEMA calculation.
2. Allow for the splice
The splice carries less than the belt itself (splice efficiency), so factor it in.
3. Match a rating above it
Choose the PIW above your calculated tension, then the covers for the material and conditions.
Use the conveyor belt calculator for speed and capacity, see heavy duty conveyor belting for ratings we supply, or send us the conveyor details for help with tension.
PIW FAQ
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, and the splice 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); standard belt conveyor engineering practice (CEMA, Belt Conveyors for Bulk Materials ).
Need a specific PIW belt?
Send the width, length, PIW or ply count, cover compound and application. As an independent distributor we cross-reference across manufacturers to match your belt.