Slings and hitches
Multi-leg sling WLL by the uniform load method (LEEA / BS EN 13414-1, BS EN 818-4)
- where
- sling assembly WLL (t)
- mode factor: 1 single leg; 2-leg 1.4 (0–45°) or 1.0 (45–60°); 3- and 4-leg 2.1 (0–45°) or 1.5 (45–60°)
- WLL of a single leg (t)
- utilisation (%)
- load to be lifted (t)
Explain this equation
Gives the rated capacity of a chain or wire rope sling with one to four legs, from the WLL of one leg and the leg angle. Use it to check that a sling is good for the load at the angle you will actually rig it.
WLL_1 is the straight-pull rating of a single leg. M is the mode factor from the LEEA uniform load method, chosen from the number of legs and the angle band (0–45° or 45–60° to the vertical). WLL_a is the rating for the whole sling, and U compares your load W with it.
The factors are stepped rather than calculated from the exact angle, so one marked rating covers any angle in the band. 1.4 and 2.1 are roughly 2 × cos 45° and 3 × cos 45°: a four-leg sling is rated as if only three legs carry the load.
Sense check: a 2-leg sling with 2 t legs is good for 2.8 t up to 45°, but only 2 t between 45° and 60°. A 4-leg sling of 3.15 t legs is good for 6.6 t up to 45°.
Watch out: over 60° is not rated at all. Don't use trigonometry to squeeze a higher rating out of a uniform-load sling.
Gives the rated capacity of a 1-, 2-, 3- or 4-leg chain or wire rope sling from the WLL of one leg, using the angle bands of the uniform load method recommended by LEEA for multipurpose slings.
Enter your values to see the result.
Good to know
Mode factors (× single-leg WLL): single leg 1; 2-leg 1.4 at 0–45° and 1.0 at 45–60° to the vertical; 3- and 4-leg 2.1 at 0–45° and 1.5 at 45–60°. A four-leg sling is rated the same as a three-leg sling because the load may be carried by only three legs. The rating is stepped: any angle within a band gets the band’s factor, so it is conservative at the low end of each band. Fibre rope slings are normally marked for the assembly instead; see the manufacturer’s label.
Common mistake
Taking the 0–45° rating when the legs are actually at 50° because “it looks about 45”. Measure or calculate the angle (see the sling angle calculator); if in doubt, use the lower band.
Limits
Uniform load method only (multipurpose slings). Single-purpose slings rated by the trigonometric method (n × WLL × cos β) are marked differently; never re-rate a uniform-load sling upward by trigonometry. Assumes legs symmetrically disposed in plan. Over 60° is not rated. Choke or basket use needs a further factor. For planning only: this does not replace a lift plan prepared by a competent person under LOLER 1998 (reg. 8) and BS 7121, and the manufacturer’s WLL markings, load charts and data always govern over this result.
Sources
- LEEA COPSULE Ed. 10, 1.A5.4 Principles for the selection of slings (uniform load method: 2-leg 0–45° ×1.4, 45–60° ×1.0; 3- and 4-leg 0–45° ×2.1, 45–60° ×1.5; 4-leg rated as 3-leg; trigonometric method 2·cos β, 3·cos β, 4·cos β)
- LEEA COPSULE Ed. 10, 15.5.2 Wire rope slings (BS EN 13414-1), method of use: choke hitch ×0.8, basket hitch with both ends on the hook 0–45° ×1.4, two single slings 0–45° ×1.4
- LEEA COPSULE Ed. 10, 14.5.2 Chain slings (BS EN 818-4), method of use: choke hitch ×0.8 of the marked SWL, basket hitch 0–45°, legs equally disposed
- The Lifting Operations and Lifting Equipment Regulations 1998 (SI 1998/2307), reg. 8: every lifting operation properly planned by a competent person, appropriately supervised and carried out safely
- HSE L113 Safe use of lifting equipment. Lifting Operations and Lifting Equipment Regulations 1998. Approved Code of Practice and guidance
Results are calculations from the published methods and figures shown, and depend on the data you enter. For planning and checking only. Scaffolds must be erected to NASC TG20 or a bespoke design by competent persons, and lifting operations planned under LOLER by a competent person. Never rely on these results instead of a design, a lift plan or manufacturer ratings.