How Legload sizes up against other sling-tension calculators
Every free sling-tension calculator on the web asks for the angle in degrees from horizontal, the one number a rigger standing on the deck almost never has. What you can't do is pull it from the tape measure already clipped to your belt. So the standard web tool stops you at the first field, and the math waiting behind it never gets a chance to help.
The angle matters because tension per leg climbs as the legs flatten out, and it climbs faster than the eye expects. At 30 degrees from horizontal the tension factor is 1/sin(30°), which is exactly 2.0: each leg carries double the share of the load it would carry on a straight vertical pick. Vendor wall charts have printed that number for decades. The gap was never the arithmetic. It was getting the angle into the arithmetic without an instrument you don't carry.
How most sling calculators ask for the angle
The degrees-from-horizontal convention comes from the engineering side of rigging, where a load chart or a lift plan states the angle directly. It's the right input when you already have a calibrated angle. On a fixed rig with a drawing in hand, you do. Between two lifts with gloves on, you don't, and that second case is the one these tools are supposed to serve. The convention quietly assumes a piece of gear that most journeymen never bought.
The tools a rigger actually compares
There are a handful of ways to land on a tension-per-leg number, and they make different bets about what you are holding when you need it.
| Tool | Input it asks for | Where it runs | Live danger cue | Cost |
|---|---|---|---|---|
| Legload | Height + leg length (degrees optional) | Any browser, no install | Color badge and diagram, redraws as you type | Free, ad-supported |
| Rigwise | Height + leg length | iOS app only | Yes, works offline | Paid app |
| LEO Rigging Calculator | Degrees from horizontal | iOS and Android | Present, buried in a 9-calculator suite | Free, ad-heavy, rated 18+ |
| Northern Strands | Height + leg length | Vendor web page | No, static result | Free, lead-gen |
| Vendor chart pages (ELT, Tway, Ashley) | A printed angle factor | PDF or web page | No, you multiply by hand | Free |
Each of these does something Legload does not, and this page names it rather than pretend otherwise. Rigwise, which launched on iOS in June 2026, runs fully offline, so it beats any web page the moment you drop into a basement or a steel canyon with no signal. LEO's app passed 21,000 downloads by bundling nine rigging calculators in one place, which earns its keep if you also size shackles and check D/d ratios on the same job. Northern Strands backs its calculator with a real sling catalog and 2- and 3-leg variants at northernstrands.com, handy when you are about to buy the hardware from them. The laminated vendor charts need no device at all, which is why a copy still rides in plenty of gang boxes. None of that makes them wrong; it makes them built for a different moment than a gloved hand on a phone between picks.
Why Legload reads height and leg length instead
Legload's default fields are the two distances a tape gives you: the vertical height from the load up to the hook, and the length of one sling leg. From a load weight W spread over n legs, tension per leg is (W / n) × (Lg / H), the tension factor is Lg / H, and the angle, if you want to see it, is arcsin(H / Lg). Take a 4,000 lb rooftop unit on a 2-leg bridle with 6 ft of height to the hook and 10 ft slings: the factor is 10 / 6, about 1.67, the angle lands near 37 degrees, and each leg carries roughly 3,330 lb. Enter a height equal to the leg length and the factor reads 1.0 at a vertical 90 degree lift, the sanity check every rigger already knows by feel.
Legload makes height-and-leg-length the default and puts the degrees field behind a toggle, because riggers on a deck measure distances, not angles. The most common mistake is entering a height larger than the leg length, which is geometrically impossible and would otherwise produce a confident, wrong angle. The tool blocks that with a plain message instead of returning a number you would trust. The diagram recolors red below 30 degrees and amber between 30 and 45, so the danger reads before you have finished the result.
The trade-off you inherit with tape-measure inputs
The tape path is only as good as your two measurements. A leg length read to the nearest inch and a height eyeballed against a column will move the derived angle by a degree or two, and down near 30 degrees a small angle error swings the tension factor more than the same error does up at 60. A calibrated inclinometer reading the angle straight off a fixed rig can be tighter than that. For a field pick where the geometry is approximate anyway, the distances you can actually measure beat an angle you have to guess at.
One thing the tool hands you is a factor, not a rated capacity. Legload assumes every leg shares the load equally, which 2-leg bridles come close to but 3- and 4-leg arrangements rarely do, so the per-leg figure on a multi-leg pick is a floor and not a promise. It's a planning and teaching aid that sits next to ANSI/ASME B30.9 and OSHA 1926.251, not a stand-in for the rated working load limit stamped on your gear or for a qualified person's sign-off. Read the factor, respect the color, and verify against the tag before the load leaves the ground.