Enter total load, number of legs, and sling angle. Get load per leg, tension factor, horizontal & vertical force, and a recommended chain sling size — instantly.
Percentage of a sling leg's vertical capacity usable at each angle (ASME B30.9). Tension multiplier = 1 ÷ factor.
| Angle from Horizontal | Capacity Factor | Tension Multiplier |
|---|---|---|
| 90° | 1.0 | × 1.000 — Vertical — no increase |
| 60° | 0.866 | × 1.155 — Standard 2-leg rigging |
| 45° | 0.707 | × 1.414 — Tension rises ~41% |
| 30° | 0.5 | × 2.000 — ASME minimum — tension ×2 |
Based on ASME B30.9. Assumes symmetric rigging with equal leg lengths. Not a substitute for qualified rigger judgment. Always verify with manufacturer data.
ASME B30.9 (Slings) governs the design, selection, and use of slings in lifting operations. Key angle-related provisions:
This calculator assumes symmetric rigging, equal leg lengths, and a centered load. Deduct fittings (hooks, master links) from rated capacity when they load the sling at an angle.
Single-leg vertical Working Load Limits for Grade 80 alloy chain slings. Select the smallest chain whose WLL meets or exceeds the calculated tension per leg.
| Chain Diameter | WLL (vertical, tonnes) | 60° angle (×0.866) | 45° angle (×0.707) | 30° angle (×0.5) |
|---|---|---|---|---|
| 6mm | 1.12 t | 0.97 t | 0.79 t | 0.56 t |
| 8mm | 2.00 t | 1.73 t | 1.41 t | 1.00 t |
| 10mm | 3.15 t | 2.73 t | 2.23 t | 1.57 t |
| 13mm | 5.30 t | 4.59 t | 3.75 t | 2.65 t |
| 16mm | 8.00 t | 6.93 t | 5.66 t | 4.00 t |
| 18mm | 11.20 t | 9.70 t | 7.92 t | 5.60 t |
| 20mm | 15.00 t | 12.99 t | 10.60 t | 7.50 t |
| 23mm | 21.20 t | 18.36 t | 14.99 t | 10.60 t |
| 26mm | 31.50 t | 27.28 t | 22.27 t | 15.75 t |
Grade 80 (T) alloy chain per EN 818-2 / ASME B30.9. Values are single-leg WLL — apply the appropriate angle factor and divide by legs for multi-leg slings, or use the calculator above.
Answers based on ASME B30.9 and standard rigging practice.
The tension factor is 1/sin(angle), where the angle is measured from horizontal. At 90° (vertical) the factor is 1.0; at 60° it is 1.155; at 45° it is 1.414; at 30° it is 2.0. Multiplying the vertical load share per leg by this factor gives the actual tension in the leg.
Only the vertical component of sling tension (T × sin θ) supports the load; the horizontal component squeezes the load. As the angle drops, the vertical component shrinks, so the total tension must grow to hold the same weight. At 30° from horizontal, each leg carries twice its vertical share — and the horizontal squeeze becomes large enough to crush or deform the load.
ASME B30.9 recommends sling angles never fall below 30° from horizontal. Below that, tension exceeds twice the vertical share and horizontal forces risk damaging the load or connections. If your hook height forces a shallow angle, use a spreader beam or lifting beam to bring the legs back toward vertical.
Measure between the sling leg and a horizontal line at the load attachment point, using a digital angle finder, an inclinometer app, or a protractor. Measure every leg in a multi-leg rig and use the shallowest angle for sizing. Never estimate by eye — small angle errors cause large tension errors.
Only when legs are the same length, attach at the same height, and the load's center of gravity is centered under the hook. Unequal lengths or an off-center CG put more load on some legs — this calculator's even-share assumption no longer applies, and a qualified person must evaluate the rig per ASME B30.9.
No. The 1/sin(angle) tension relationship is geometry, not material — it applies equally to chain, web, and wire rope slings. What changes is the rated capacity at 90° (vertical): chain slings are rated per the chart above, while web and wire rope slings follow their own WLL tables. See our Sling Capacity Chart for web and wire rope values.
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Disclaimer: All calculations on this page are for preliminary reference only and are based on ASME B30.9 with the simplifying assumption of symmetric, equal-leg rigging. Actual rigging capacity depends on manufacturer ratings, component condition, environmental factors, and rigging geometry. This tool does not replace the judgment of a qualified rigger or competent person. Always verify with manufacturer data and applicable regulations before any lift. riggingcalculators.com accepts no liability for decisions made using these calculations.
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