A catalogue may show 1770 MPa beside 78.2 kN, but those figures answer different questions. The MPa heading identifies a nominal strength class in this catalogue. The 78.2 kN entry is the listed minimum breaking load for one specified rope construction, diameter and core. Neither number is a permitted working load.
To compare ropes, first find the correct catalogue row and core. Then check the finished rope’s breaking-force requirement against the equipment and job rules. The charts below use values from Powerful Machinery’s catalogue to show how to read them.
What Is Wire Rope Tensile Strength?
Tensile strength is resistance to pulling stress, expressed as force per unit area. For steel wire, it is commonly stated in MPa or N/mm²; 1 MPa equals 1 N/mm². A catalogue may also place values such as 1570, 1770 and 1960 MPa above its rope breaking-load columns. In this article, those headings identify the catalogue’s nominal strength classes.
They are not breaking forces or measured tensile strengths for every wire in a finished rope.
A finished rope contains strands, wires, a core, and spaces between them. Its specified minimum breaking force is a force, usually given in kN. Two ropes with the same nominal diameter and MPa heading can have different breaking loads because their constructions or cores differ. For a closer look at those arrangements, see our steel wire rope construction guide.
The word ‘grade’ needs care. Under standards that define rope grade, the number denotes a minimum breaking-force requirement for a defined rope. Wire tensile grade describes a range of tensile strengths for the constituent wire. A rope marked grade 1960 does not mean every wire tested at exactly 1960 MPa.
Powerful Machinery’s catalogue labels its MPa columns ‘nominal tensile strength of rope’; confirm the applicable product standard and grade designation for the rope being quoted rather than assuming that heading names a constituent-wire test result.
Tensile Strength vs Breaking Strength, MBF, MBL and WLL
Start with the unit and ask whether the figure applies to a wire, a finished rope, or the installed system.
| Term | What it means | Unit |
| Wire tensile grade | Specified tensile-strength level of a constituent wire | MPa / N/mm² |
| Rope grade | Breaking-force requirement class under the applicable standard; not an individual-wire test result | grade designation |
| Minimum breaking force/load (MBF / MBL) | Specified minimum for the defined finished rope | kN / lbf |
| Measured breaking force | Result of a particular destructive test on the rope | kN / lbf |
| WLL / SWL | Permitted rating for the defined application or assembly | kN / kg / t |
| Design factor | Required relationship in the particular equipment/application rule | dimensionless |
‘Breaking strength’ is less precise than it sounds. A catalogue may use it for the specified minimum breaking force, while a test report may give the force actually measured when a specimen breaks. Ask which figure a supplier means.
The specified minimum is a requirement for a defined new rope, not a promise that every specimen fails at that exact force. Test results also depend on the specimen and test setup, including the end attachments.
WLL, or working load limit, is a rating for the intended application or assembly. Older material may call it SWL, or safe working load. Neither is the MPa heading divided by a standard number. The applicable equipment rules, design factor, terminations, reeving, and operating conditions all matter.
Do not use the bare rope’s minimum breaking load as its working rating. Our wire rope working-load guide explains that selection step in more detail.
Wire Rope Tensile Strength Grades Explained
The catalogue lists nominal MPa classes of 1570, 1670, 1770, 1870 and 1960. Under each heading, it gives separate minimum breaking loads for fiber-core and steel-core options. Select the class, diameter and core together; the resulting kN cell is the catalogue value for that row. The MPa heading cannot be converted directly into a rope’s breaking load or working load.
| Catalogue nominal class | How to use it |
| 1570 MPa | Choose its column, then the matching diameter and core. |
| 1670 MPa | A separate catalogue column; omitted from the condensed charts below. |
| 1770 MPa | Used for the cross-construction examples and reading exercise. |
| 1870 MPa | A separate catalogue column; omitted from the condensed charts below. |
| 1960 MPa | Higher nominal class in these tables; still requires its own kN cell. |
IPS means Improved Plow Steel; EIPS means Extra Improved Plow Steel; and EEIPS means Extra Extra Improved Plow Steel. These rope-grade names appear in ASTM/API specifications. They do not translate into one fixed MPa value for every constituent wire, and they should not be treated as exact substitutes for the metric headings in this catalogue.
If a quotation says ‘EIPS 1770 MPa,’ ask for the governing standard, the stated rope grade, the wire specification and the finished rope’s minimum breaking force.
Wire Rope Tensile Strength Charts by Diameter, Construction and Grade
The charts below excerpt the catalogue’s ‘minimum breaking load of rope’ tables. All forces are in kN and describe new rope specifications; they are neither working-load limits nor order-specific test results. Several catalogue pages place related construction drawings above a shared load table.
Where a table says ‘IWR/IWS,’ check the exact core and construction on the current technical sheet before using its figure for an order or an engineering decision.
To keep the charts readable, each one shows selected diameters and four columns: 1570 MPa with FC, 1770 MPa with FC, 1770 MPa with the listed steel core, and 1960 MPa with FC. The catalogue also has 1670 and 1870 MPa columns. Consult the full table for those grades or other diameters; do not estimate an omitted figure from this excerpt.
6×7 Wire Rope Strength Chart
On printed page 78, the catalogue shows 6×7 drawings with FC and IWS cores, alongside 6×9W variants. The load table uses a shared ‘IWR/IWS’ steel-core heading. The IWS figures below follow the pictured 6×7+IWS option, pending confirmation of the exact quoted variant.
| Diameter mm | 1570 MPa FC kN | 1770 MPa FC kN | 1770 MPa IWS kN | 1960 MPa FC kN |
| 6 | 18.7 | 21.1 | 22.8 | 23.4 |
| 10 | 52.1 | 58.7 | 63.5 | 65 |
| 16 | 133 | 150 | 162 | 166 |
| 20 | 208 | 235 | 254 | 260 |
| 24 | 300 | 338 | 366 | 374 |
| 32 | 533 | 601 | 650 | 666 |
Source: Powerful Machinery catalogue, printed page 78 (PDF page 81). Values are minimum breaking load of rope, not WLL.
At 10 mm and 1770 MPa, the table gives 58.7 kN for FC and 63.5 kN for its IWR/IWS steel-core column. That difference applies to this catalogue row. It should not be turned into a fixed percentage for other rope designs.
6×19 Wire Rope Strength Chart
Printed page 79 shows the 6×19 family with FC, IWR and IWS drawings. Its breaking-load table combines the latter two under ‘IWR/IWS.’ Specify which core you need when asking for a quotation.
| Diameter mm | 1570 MPa FC kN | 1770 MPa FC kN | 1770 MPa IWR/IWS kN | 1960 MPa FC kN |
| 6 | 17.4 | 19.6 | 21.2 | 21.6 |
| 10 | 48.2 | 54.3 | 58.8 | 60 |
| 16 | 123 | 139 | 150 | 154 |
| 20 | 193 | 217 | 235 | 240 |
| 24 | 278 | 313 | 338 | 346 |
| 32 | 494 | 556 | 602 | 616 |
Source: Powerful Machinery catalogue, printed page 79 (PDF page 82). Values are minimum breaking load of rope, not WLL.
The full 6×19 table gives 78.2 kN for a 12 mm FC rope at 1770 MPa, compared with 84.6 kN in its IWR/IWS column. The reading example below uses the FC figure. See the 6×19 steel wire rope product page for the product family, and confirm the quoted variant against its current specification.
6×37 Wire Rope Strength Chart
Printed page 80 shows the 6×37 family with FC, IWR and IWS drawings. Again, the load table combines the steel-core options in one column.
| Diameter mm | 1570 MPa FC kN | 1770 MPa FC kN | 1770 MPa IWR/IWS kN | 1960 MPa FC kN |
| 6 | 16.7 | 18.8 | 20.3 | 20.8 |
| 10 | 46.3 | 52.2 | 56.5 | 57.8 |
| 16 | 119 | 134 | 145 | 148 |
| 20 | 185 | 209 | 226 | 231 |
| 24 | 267 | 301 | 325 | 333 |
| 32 | 474 | 535 | 578 | 592 |
Source: Powerful Machinery catalogue, printed page 80 (PDF page 83). Values are minimum breaking load of rope, not WLL.
For a 20 mm FC rope at 1770 MPa, the 6×37 table lists 209 kN; the 6×19 table lists 217 kN. Matching diameter, class, and core do not make the constructions interchangeable. Use the row for the rope actually specified.
Line-Contact, Elevator and Rotation-Resistant Ropes
The next examples come from separate catalogue tables. Each uses a nominal diameter of 12 mm and the 1770 MPa column. The different breaking loads show why you must identify the rope family, but they do not establish that one construction can replace another.
| Catalogue family at 12 mm | Core | 1770 MPa minimum breaking load |
| 6×19S / 6×19W line-contact family | FC | 84.1 kN |
| 8×19S / 8×19W elevator family | FC | 74.6 kN |
| 18×7 / 18×19 multi-layer family | FC | 79 kN |
| 35W×7 multi-layer rope | Not specified in table | 91.8 kN |
Sources: catalogue printed pages 81, 84 and 86 (PDF pages 84, 87 and 89). Related construction drawings share some tables; the 35W×7 figure comes from its own table, which does not name a core. Confirm the exact construction and core before specifying a rope.
The line-contact page shows 6×19S and 6×19W variants above a shared table; the elevator page does the same for 8×19S and 8×19W. On the multi-layer page, 18×7 and 18×19 share one table, while 35W×7 has its own. Confirm the exact variant and intended use with the supplier.
Lift ropes have their own requirements: ISO 2408 excludes them, while ISO 4344 addresses steel wire ropes for lifts. Rotation-resistant rope likewise needs selection and handling instructions beyond the breaking-load figure.
How Diameter, Construction and Core Affect Breaking Strength
Within the same construction family, core and MPa class, a larger diameter generally has a higher listed minimum breaking load. In the 6×19 FC table at 1770 MPa, the figure rises from 19.6 kN at 6 mm to 217 kN at 20 mm. Change the construction, core or class and you need to read a different cell; diameter alone will not give you the answer.
Construction describes how the strands and wires are arranged. That arrangement affects the rope’s metallic area, contact between wires and bending behavior. Treating its outside diameter as the diameter of a solid steel bar would count the core and open spaces as metal.
A fill factor helps describe metallic area, but it is no substitute for the rope’s specified minimum breaking force. If you also need to consider sheaves, drums or the operating environment, see our wire rope selection guide.
FC means fiber core and IWS means independent wire strand core. This catalogue also uses IWR for a wire-rope-core option and groups some steel-core values under ‘IWR/IWS.’ Other technical sources commonly use IWRC for independent wire rope core.
Do not assume the shared table cell identifies a specific IWR or IWRC product. Steel-core figures are often higher than FC figures in the same catalogue row, but the difference varies. Choose the core for the machine and operating conditions as well as the required breaking force.
How to Read a Wire Rope Strength Chart
Say you are checking a 12 mm rope in the catalogue’s 6×19 family, with FC and the 1770 MPa class. Find the 12 mm row, then follow it across to the FC subcolumn under 1770 MPa. The minimum breaking load is 78.2 kN. The adjacent IWR/IWS figure, 84.6 kN, belongs to the steel-core column and cannot be assigned to the FC rope.
Next, check how the rope will be used. Confirm the equipment standard, terminations, reeving and any other assembly details. A competent person can then assess the allowable operating load for the complete system. If you need current production data or an order-specific document, request it for the exact quoted rope. The 78.2 kN catalogue figure does not authorize a 78.2 kN lift or establish a WLL.
For calculation questions, separate the manufacturer’s rope specification from the system rating. The specified minimum breaking force comes from a defined rope design and applicable test or calculation method. The permissible working load depends on the equipment and application rules. Outside diameter multiplied by an MPa value does not give a reliable working rating for a wire rope.
How Is Wire Rope Strength Tested?
Testing a wire and breaking a finished rope answer different questions. A wire tensile test checks properties against its wire specification. In a finished-rope test, a secured specimen is pulled until it breaks; its measured breaking force can then be checked against the rope’s specified minimum.
ISO 3108:2017 describes this destructive test for steel wire ropes, and ASTM A931-18 covers tension testing of wire ropes and strands. The test setup, particularly the end attachments, can affect the result.
ISO 2408:2017 sets requirements for the rope types within its scope, including manufacture, testing and acceptance. Mentioning a standard does not establish which test or certificate applies to Powerful Machinery’s products.
Ask which product standard and test method govern the exact rope, and what documentation is available with your order. See our wire rope certification overview for document types and questions to ask.
How to Select the Required Wire Rope Strength?
Start with the equipment and its duty. Is the rope for a crane, hoist, winch, lift, sling or another use? Record the operating load and the conditions that affect selection, including reeving, acceleration, bending over sheaves, drum size and end fittings. A catalogue breaking-load figure alone cannot show whether a rope will suit the machine.
Find the standard and rating method that govern that application. Use them to determine the required minimum breaking force, taking terminations and the complete assembly into account where applicable. Then compare ropes by construction, diameter, core, nominal class, finish, lay and stated minimum breaking force. Ask for the current technical sheet and the documentation required for the order.
There is no single design factor for every wire-rope use. A rope on a crane, a finished sling and a lift rope may each be subject to different rules. For an existing machine, check the machine manufacturer’s requirements and have the selection assessed by a qualified person.
To request a quote, send Powerful Machinery the application, rope construction or existing part identification, diameter, core, grade, required breaking force, operating conditions and quantity through the contact form. You can browse the steel wire rope range for available constructions.
FAQs
What is the tensile strength of steel wire rope?
There is no single tensile-strength value for every steel wire rope. A catalogue may give a nominal class such as 1570, 1770 or 1960 MPa and a separate minimum breaking force in kN. To find the relevant figure, identify the construction, diameter, core and class, then confirm the exact product specification.
What is the difference between tensile strength and breaking strength?
An MPa value describes tensile stress or a nominal strength class, depending on the specification. A finished rope’s minimum breaking force is stated in units of force, such as kN; a measured breaking force is the result of a destructive test. These figures are related, but none is the permitted working load of an installed system.
What do 1570, 1770 and 1960 MPa mean in a wire rope table?
In this catalogue, they are headings for nominal strength classes. Choose the appropriate class, diameter and core to find the listed minimum breaking load in kN. The heading does not mean every wire in the rope has an actual measured tensile strength equal to that number. Confirm how the grade is defined in the specification for the rope you plan to buy.
What is the difference between IPS, EIPS and EEIPS wire rope?
IPS, EIPS and EEIPS mean Improved, Extra Improved, and Extra Extra Improved Plow Steel. They are rope-grade names in a different specification system, not exact conversions to 1570, 1770 or 1960 MPa wire grades. Compare quotes using the governing standard, full construction and stated minimum breaking force.
What is the tensile strength of 3/16-inch wire rope?
3/16 inch is a nominal diameter of about 4.76 mm, not a strength rating. Ropes of that size can differ in construction, core, material, and grade. You cannot round 3/16 inch to a 5 mm catalogue row and assign its breaking force to the imperial-size rope. Use the manufacturer’s specification for the exact product.
Can WLL be calculated directly from wire rope tensile strength?
No. An MPa figure does not by itself state the finished rope’s minimum breaking force, and that force does not establish the working rating for every system. Check the exact rope specification and apply the rules for the equipment, design factor where required, terminations and operating conditions. A competent professional should approve the selection for lifting service.
Conclusion
Read the MPa heading as a nominal catalogue class, then find the kN minimum breaking load for the specified construction, diameter and core. That gives you a figure to compare with the requirements for your equipment; it is not a WLL. For a quotation, share the complete rope specification and application so Powerful Machinery can confirm the current product data.
