How the percent of capacity is worked out
Percent of capacity compares what the crane is carrying with what the chart says it can carry in that exact setup. Three steps:
- Read the chart capacity. Use your crane's own chart for its configuration, the loaded radius and the boom length. A chart number only holds for the configuration it was printed for.
- Add up the total. Total = load + rigging + hook block + any jib or attachment allowance + other deductions your chart notes call for. The calculator adds the five boxes for you.
- Divide and flag. Percent = total ÷ chart capacity × 100. The two flags go off at or above the marks you type in. They start at 75% and 90%, which are common lift-plan marks. They are not a rule from OSHA or from a crane maker, so use the ones your own lift plan sets.
Why the deductions go in the total: the block and rigging add to what the boom carries along with the load. The net capacity calculator works the same lift the other way round, by taking the deductions off the chart number first. If you are not sure what the load itself weighs, the load weight calculator estimates it and adds the rigging. Not sure which row to read? Start with how to read a crane load chart.
OSHA 29 CFR 1926.1417 covers operating a crane within its rated capacity and following the manufacturer's procedures, so confirm the details against it and your own chart.
Worked example 1: well inside the marks
Invented numbers. The chart capacity at the radius is 24,000 lb. The load is 12,000 lb, the rigging is 450 lb, the hook block is 600 lb and the stowed jib allowance is 800 lb. Total = 12,000 + 450 + 600 + 800 = 13,850 lb. Percent = 13,850 ÷ 24,000 × 100 = 57.7%. That is below 75%, so no flag. The total would have to reach 18,000 lb to hit 75%, so there are 4,150 lb of room to that mark.
Worked example 2: past the first mark
Invented numbers. A shorter boom setup has a chart capacity of 18,000 lb. The load is 12,000 lb, rigging 600 lb, hook block 700 lb and jib allowance 500 lb. Total = 13,800 lb. Percent = 13,800 ÷ 18,000 × 100 = 76.7%. That is past 75% and under 90%, so the first flag shows. The total sits 300 lb over the 75% mark (13,500 lb) and 2,400 lb under the 90% mark (16,200 lb).
These are original arithmetic examples, not exam questions and not any crane's chart.
Crane percent of capacity questions
What percent of capacity is too much for a crane lift?
The chart rating is the limit, and 100% of it is the most the chart allows for that setup. Many lift plans add their own lower marks, and 75% and 90% are common ones, but they are a planning habit and not a rule. Your employer's lift plan, your crane's manual and the person in charge of the lift decide what applies.
Do I include the hook block and rigging in the load?
Yes, count everything the chart says reduces the capacity: the load, the rigging, the hook block and any jib or attachment allowance. Some charts already build part of that in, so read the notes on your chart. Enter 0 for anything your chart has already counted so it is not counted twice.
How is this different from net capacity?
Net capacity subtracts the deductions from the chart number first and then compares the load alone to what is left. Here the deductions are added to the load and the total is compared to the chart number. Both views describe the same lift, so the percent differs even though nothing about the lift changed. The net capacity calculator shows the subtraction one step at a time.
Taking a load from the weight on the tag to a percent of chart is the kind of reasoning the written exam tests. This tool shows the arithmetic and does not approve a lift.