How to use this calculator
- Read the vertical WLL off the tag. The single-leg vertical rating — the basis every factor multiplies.
- Pick the hitch. Vertical, choker (wrapped and cinched) or basket (cradled, both eyes up).
- Match the factors to your tag. 75% / 200% are the standard card values; your tag or chart may say otherwise — enter what it says, including D/d-reduced basket factors.
- Apply the leg angle. Basket legs off vertical multiply by sin θ; below 45° re-rig rather than calculate.
How it works
Every sling has one number on the tag — the vertical rating — and the hitch turns it into the number that matters for the pick:
choker ≈ 0.75 × WLL · basket ≈ 2 × WLL × sin θ (legs near vertical, D/d met)
The factors are the standard rigging-card values, kept adjustable because the sling's own tag governs. Multi-leg bridles and the tension each leg actually sees live in the sling angle load calculator, two-point load share in the rigging CG calculator, and the load's weight itself in the metal weight calculator.
Worked example
Verified against the live calculator
A 2-tonne (19.6 kN) vertical-rated sling, standard card
factors:
choker = 2 × 0.75 = 1.5 t · basket (vertical legs) = 2 × 2.0 = 4 t · basket at 60° = 4 × sin 60° = 3.46 t
Same sling, three working numbers. The basket's doubled rating is conditional — both legs near vertical and the bend meeting the tag's D/d minimum — and the angle factor erodes it fast: at 45° the 4 t basket is down to 2.83 t, and below that most crews re-rig rather than lean on the multiplier.
Frequently asked questions
How much does a choker hitch reduce sling capacity?
To about 75–80% of the vertical rating on standard capacity cards — a 2-tonne sling chokers at roughly 1.5 t. The reduction comes from the bend and cinch at the choke point, and choke angles under about 120° (load cinched hard back on itself) cut it further per the maker's chart.
Why is a basket hitch rated at 200%?
Both legs share the load, so with the legs effectively vertical the sling carries twice its single-leg rating — the same 2 t sling baskets at 4 t. The two conditions card values demand: legs near vertical, and the bend diameter meeting the tag's D/d minimum. Spread the legs and capacity multiplies by sin θ: 60° legs take the 4 t basket to 3.46 t.
What is the D/d ratio and why does it matter?
Bend diameter over rope/sling body diameter. Bending a sling around a small pin or edge weakens it well below the tag rating — wire rope baskets commonly want D/d around 25 for full capacity. When the bend is tighter, the maker's chart gives a reduced basket or choker factor: enter that reduced percentage here.
Does this replace the sling tag or chart?
No — it runs the card arithmetic so you can plan, with the factors adjustable to match YOUR sling's tag. The tag, the maker's chart and ASME B30.9 govern the lift; when this screen and the tag disagree, the tag wins, every time.
Method & assumptions
- Standard capacity-card hitch factors (verified against rigging references and sling-maker guidance in the ASME B30.9 frame), user-adjustable — the sling tag and maker chart govern; this screen never overrides them.
- Basket 200% assumes both legs effectively vertical and the tag's minimum D/d met at the bend; choker factors assume choke angles ≳120°. Tighter bends and harder chokes take the maker's reduced values — enter those.
- Symmetric, freely-hanging hitches; edge loading, softeners, sharp corners, temperature and chemical exposure follow the sling maker's rules.
- Planning arithmetic, not a lift plan: inspection, rigging practice and the qualified person remain ASME B30.9 / OSHA territory.