Sling Tension Calculator
Load, legs, and angle to tension per leg.
What it does
A two-leg bridle at a flat angle can pull harder on each leg than the whole load weighs. Angle multiplies force through the sine, so shallow slings snap while steep ones cruise. One division previews the danger.
The tool above divides the load by legs times sine of the angle and checks the vector sum back to the load. Imperial mode works in pounds; metric mode works in kilograms. It also flags shallow angles under 30 degrees.
OSHA rigging guidance and the ASME B30.9 sling standard both demand rated slings, angle awareness, and qualified riggers. The math here mirrors their tables: vertical legs share evenly, 60 degrees sips, 30 doubles, and below that tension runs away.
Use it to sanity-check a plan, then rig above the answer. Uneven legs, stretch, and shock all push peaks past the even-share math, so margin and training carry every real lift.
How to use
- Pick imperial (lb) or metric (kg).
- Enter the total load weight.
- Enter sling legs sharing it.
- Enter the sling angle from horizontal.
- Read tension per leg and the vector check.
- Rig only rated slings above that tension.
Formula
- load
- Total hung weight in lb (kg metric).
- legs
- Count of sharing sling legs, 1 to 4.
- angle
- Sling angle above horizontal, 15 to 90 degrees.
Angle sits in degrees from horizontal with sine applied. Single-leg vertical lifts carry the full load. Results assume equal legs sharing evenly with no shock loading; real lifts add angle, wear, and hitch factors.
Worked example
Example: 2000 lb, 2 legs, 60 deg
2000 lb load hung from 2 sling legs at 60 degrees to horizontal.
- Load is 2000 lb on 2 legs at 60 degrees.
- Sine of 60 is 0.866.
- Tension: 2000 / (2 x 0.866) = 1,155 lb per leg.
- Check: 2 x 1155 x 0.866 = 2,000 lb vertical.
- Read: steep angle, low tension, rig below rated slings.
Reference table
| Angle | Each leg carries | Note |
|---|---|---|
| 90 deg | 0.50 x load | Vertical, even share |
| 60 deg | 0.58 x load | Steep and kind |
| 45 deg | 0.71 x load | Typical bridle |
| 30 deg | 1.00 x load | Doubles here |
| 20 deg | 1.46 x load | Extreme, avoid |
Limits
- Even sharing assumed. Uneven legs break the math.
- Static only. Shock and swing add peaks.
- No hitch, wear, or temperature factors.
- A check, not a lift plan or sign-off.
Common mistakes
- Reading the angle from vertical instead of horizontal.
- Rigging under 30 degrees.
- Rating the bridle by total instead of per leg.
- Ignoring stretch on rope slings.
- Skipping a qualified rigger.
Try it yourself
Quick checks. Answers sit tucked under each question.
Tension for 3000 lb on 3 legs at 45 deg?
Sine of 45 is 0.707. Tension is 3000 / (3 x 0.707) = 1,414 lb per leg.
Tension for 1000 lb on 2 legs at 25 deg?
Sine of 25 is 0.423. Tension is 1000 / (2 x 0.423) = 1,183 lb per leg: shallow, extreme tension.
Questions
What is the sling angle formula?
Tension per leg equals load divided by legs times sine of the angle. At 90 degrees each leg carries its even share; at 30 degrees each carries double; below that it explodes.
Angle from horizontal or from vertical?
From horizontal, the standard in rigging tables. A 60-degree included angle reads as 30 here, so confirm which one the chart uses before trusting it.
When does the angle turn dangerous?
Below about 30 degrees from horizontal. Tension doubles at 30 and triples near 20, so most rules never rig under 30.
How do I pick a sling from the tension?
Rated load divided by the tension with margin to spare. A 1155 lb leg needs slings rated above that each, plus the angle and wear factors the shop applies.
Does the math cover uneven legs?
No. Uneven legs, stretchy rope, shock loads, and off-center hooks all raise the peak leg above the math. Equalize carefully and add margin for real lifts.
What rules govern real lifts?
OSHA rigging guidance and ASME B30.9 sling rules both require rated slings, trained riggers, and angle awareness. This page checks arithmetic; a qualified person signs the lift.