Rigging & Staging calculator
Hang Point Load Calculator
When a truss hangs from several points, each load between two points splits to them by the lever rule: the closer point takes the bigger share, in proportion to the distances. This calculator reports exact two-point reactions and adjacent-span estimates for three or four hang points.
Two-point pickups use exact moment equilibrium, including overhangs. Three- and four-point pickups use the adjacent-span approximation; a continuous truss redistributes further. Statics only; capacity, deflection, and hardware belong to a qualified rigger or engineer.
Formulas
Lever rule between adjacent points
P(near) = W × d(far) / span, P(far) = W × d(near) / span- W:
- load between the two points
- d(near), d(far):
- distances from the load to each point
Tributary distributed load
each point carries the UDL from half of each adjacent span (plus any overhang)- UDL:
- uniform weight in lb per ft
How it works
Two points are pure statics with a single answer, so this tool balances both force and moment across the full truss, including overhangs. Three or more points over one continuous stick make the structure statically indeterminate: the real distribution depends on truss stiffness and on how evenly the motors bring the points to trim. The adjacent-span method used here is the standard field approximation: treat each bay between points as its own simple span.
The approximation errs a few percent against a full continuous-beam solution, and real rigs err further: a motor an inch high at trim steals load from its neighbors. That is exactly why critical rigs get load cells under the points rather than trust in arithmetic.
On a two-point pickup, loads on an overhang can increase the near reaction and unload the far support; a negative result means uplift. For three- and four-point estimates, point loads outside the outermost hangs remain out of scope.
Worked example: 60 ft stick at 12 lb/ft on points at 5, 25, and 45 ft; 400 lb at 15 ft, 300 lb at 40 ft
- 1.Tributary UDL: point A covers 0-15 ft (180 lb), B covers 15-35 ft (240 lb), C covers 35-60 ft (300 lb).
- 2.400 lb at 15 ft sits midway in the 5-25 span: 200 lb to A, 200 lb to B.
- 3.300 lb at 40 ft sits 3/4 along the 25-45 span: 75 lb to B, 225 lb to C.
Point A ≈ 380 lb, point B ≈ 515 lb, point C ≈ 525 lb.
Lever-rule split for a load between two points 20 ft apart
| Load position from point A | Point A share | Point B share |
|---|---|---|
| 5 ft | 75% | 25% |
| 10 ft | 50% | 50% |
| 15 ft | 25% | 75% |
| 18 ft | 10% | 90% |
Field notes
- Plot the heaviest fixtures near points, not mid-bay; the same fixture mid-bay adds bending the truss must carry.
- When one motor of a multi-point pickup stalls or leads, load redistributes instantly; competent motor ops watch chains, not just pickles.
Frequently asked questions
How is weight shared between two hang points?
By inverse distance: a load 3 ft from one point and 9 ft from the other puts 75% on the near point and 25% on the far one. Equal distances split equally.
Why do my load cells not match the calculation?
Continuous trusses redistribute load with stiffness, and trim height differences of fractions of an inch move hundreds of pounds between points. Calculations set expectations; cells report reality.
Can I use this for points on a bridle?
No; this distributes vertical loads along a truss. Bridle leg tensions involve angles and grow past the supported weight as legs flatten; use the bridle calculator for that geometry.