How to read a crane load chart
Find the chart for your exact crane and configuration, pick the boom length and radius, read the gross capacity where they meet, subtract the weight of the hook block, rigging and anything else hanging from the boom, and compare the result with the load. Gross capacity minus deductions equals net capacity (American Crane School). The load must never exceed the net figure (OSHA 1926.1417).
A crane’s headline capacity, say 40 tons, is the most it can lift under the best conditions, close in with a short boom. Nobody lifts at those conditions for long. What you can actually lift at the radius and boom length of your job is in the load chart, and reading it correctly is the difference between a routine lift and an incident. This guide walks through it step by step, with a worked example using made-up numbers. It complements our guide to crane planning and heavy lifts in Sint Maarten, which covers the wider lift plan.
One caution before we start. This is an explainer for owners, riggers and planners. The chart in the cab of the crane you’re using is the authority, and lifting decisions belong to the qualified operator and lift director.
What does a crane load chart show?
A load chart shows the rated capacity of a specific crane for every approved combination of boom length, radius and configuration. On a typical chart the boom lengths run along the top row and the operating radii run down the left column (American Crane School). The larger the radius, the lower the capacity, and a longer boom at the same radius generally carries less (SANY).
| Radius | 70 ft boom | 90 ft boom |
|---|---|---|
| 30 ft | 41,000 lb | 36,500 lb |
| 40 ft | 31,500 lb | 29,000 lb |
| 50 ft | 25,000 lb | 24,000 lb |
| 60 ft | 20,000 lb | 19,000 lb |
| 70 ft | Not permitted | 15,500 lb |
The table above is an invented mini chart, for practice only. Real charts add a page for each configuration, such as outriggers fully extended, on tires, or with a jib fitted, and the operator must use the page that matches the crane’s actual setup.
How do you read a load chart, step by step?
Work through the same six steps every time. The American Crane School’s rule comes first: never swap load charts or use one that doesn’t belong to the specific crane (American Crane School).
Model, counterweight, outriggers, jib and working area. Use only that crane’s chart.
Read across the top row of the chart to the boom length you’ll use.
The horizontal distance from the crane’s center of rotation to the load. Read down the left column.
The number where the radius row meets the boom length column, or the boom angle and radius columns.
Hook block or ball, rigging, hanging rope and any jib, erected or stowed. That leaves net capacity.
The load, including rigging, must be less than net capacity. Then check the chart’s footnotes.
The radius is the step people get wrong most often. It’s measured to the load, not along the boom, and a boom bends under load, which adds a little to the real radius. Measure from the actual setup, and allow for it.
What is the difference between gross and net capacity?
Gross capacity is the figure printed on the chart. It covers everything hanging from the boom tip, including the hook block, headache ball, rope, slings, shackles and the load itself (SANY). Net capacity is what’s left for the load after those items come off: gross capacity minus deductions equals net capacity (American Crane School).
In the example, a 24,000 lb gross capacity loses 900 lb to the hook block, 350 lb to rigging and 1,150 lb to a stowed jib. That leaves 21,600 lb net, so a 20,000 lb load fits with 1,600 lb to spare. Notice that a jib counts even when it’s stowed on the boom and not in use.
What does the bold line on a load chart mean?
The bold line separates two different limits. Capacities above the bold line are limited by the crane’s structural strength, and capacities below it are limited by stability, meaning the crane would tip before something broke (SANY). Each chart has its own way of marking the difference (American Crane School).
The distinction matters because the two limits behave differently. A tipping limit gives warning as the crane gets lighter on its outriggers. A structural limit can fail without much warning. Either way, the chart’s numbers are the ceiling, not a target.
Why do the chart’s notes matter?
Because the numbers only apply under the conditions the notes describe. Deduction tables, parts of line, working over the front versus over the side and wind limits all sit in the notes and accompanying tables (SANY). The American Crane School puts it plainly: an important part of understanding a load chart is to read the footnotes (American Crane School).
On the legal side, the U.S. OSHA crane rule requires that load charts be readily available in the cab at all times, that the equipment not be operated beyond its rated capacity, and that the operator verify the load’s weight from a recognized source or by an equally reliable means (OSHA 1926.1417). It’s U.S. law, but it’s a sensible benchmark for any crane site.
What mistakes do people make?
Five mistakes cover most of the trouble, and each is avoidable with a written lift plan:
- Using the wrong chart for the crane, its counterweight or its configuration.
- Reading the wrong radius, for example measuring along the boom or forgetting boom deflection.
- Forgetting deductions, especially the hook block, rigging and a stowed jib.
- Treating the load weight as a guess. Get it from a documented source.
- Ignoring the notes, including wind limits and configuration requirements.
What changes on a Caribbean site?
Wind and ground. Wind limits sit in the chart’s notes, and Caribbean sites are often exposed, so check the wind against the limit for the actual boom length and stop when it’s exceeded. Ground is the other one. A chart assumes the crane is set up level on adequately supported ground, and coastal sites can have soft fill, so the outrigger support needs to be checked and matted before you trust the numbers. Both points are our reading of standard practice, not part of the chart.
If you’re planning heavy lifts, our refinery heavy lift and crane rental services come with lift plans. Lift planning is also a work package in a shutdown, as in our turnaround planning checklist. And for arrays and steel frames in hurricane season, see our note on hurricane-rated solar mounting.
- Use the chart for the exact crane and configuration. Never swap charts.
- Capacity falls as radius grows, and a longer boom carries less at the same radius.
- Gross capacity minus deductions equals net capacity. The load must fit inside it.
- Deductions include the hook block, rigging, hanging rope and any jib, even stowed.
- Above the bold line the limit is structural. Below it, the limit is stability.
- Read the notes, including wind limits, and check the ground under the outriggers.
Frequently asked questions
Planning a heavy lift in the Caribbean?
Tasweldermechanics provides crane rental, heavy lift and rigging support across the Caribbean, mobilized from Sint Maarten. Tell us the load, radius and site.
Request a quoteView crane rental
EN
ES