Every crane has a load chart. It is the single most important document governing what the crane can and cannot do on any given job. And yet most contractors who hire cranes have never read one. They hand the job details to the crane operator, trust that the operator will figure it out, and move on.
That trust is usually well placed. A good operator lives by the load chart and will not exceed it. But a contractor who understands the basics of a load chart is a better partner on lift day, makes smarter equipment decisions during the planning phase, and catches potential problems before the crane shows up instead of after.
Here is how a crane load chart works and what the numbers actually mean.
What a Load Chart Tells You
A crane load chart is a table published by the crane manufacturer that shows the maximum weight the crane can safely lift at a given combination of boom length and radius. Every crane model has its own chart, and the numbers change based on the crane’s configuration (outriggers extended, outriggers retracted, on rubber, boom only, boom plus jib).
The chart answers one question: at this boom length and this distance from the crane’s center pin, how much weight can the crane pick up without exceeding its structural and stability limits?
If the load exceeds the chart value at the planned boom length and radius, the crane cannot make the lift safely. Period. There is no judgment call. There is no “it will probably be fine.” The load chart is the law of the machine.
The Two Axes: Boom Length and Radius
Radius
The radius is the horizontal distance from the center of the crane’s rotation (the center pin) to the center of the load. It is not the distance from the crane’s bumper or from the nearest outrigger. It is measured from the pivot point of the crane’s superstructure.
Radius is the most important variable on the load chart because it has the largest effect on capacity. A crane that can lift 50,000 pounds at a 10-foot radius might only lift 8,000 pounds at a 50-foot radius. The capacity drops steeply as the radius increases because the farther the load is from the crane’s center, the greater the tipping moment.
This is the number that catches contractors off guard most often. They know the load weighs 5,000 pounds and the crane is rated for 30 tons, so they assume there is a huge margin. But if the load needs to be placed 60 feet from the crane, the capacity at that radius may be only 6,000 pounds. The margin is not 55,000 pounds. It is 1,000 pounds. That changes everything about how the lift is planned.
Boom Length
The boom length is the total length of the crane’s boom from the pivot at the base to the tip. Most cranes have telescoping booms that can extend to different lengths. Longer boom lengths allow the crane to reach higher or farther, but they also reduce the crane’s capacity because the longer boom weighs more and creates a greater overturning moment.
The load chart shows capacity at each combination of boom length and radius. A crane with its boom at 60 feet and a 30-foot radius will have a different capacity than the same crane with its boom at 80 feet and the same 30-foot radius. The longer boom reduces the available capacity even at the same radius because the additional boom weight uses up some of the crane’s structural margin.
Reading the Chart: A Walk-Through
A typical load chart is organized as a grid. The left column lists boom lengths (40 feet, 50 feet, 60 feet, and so on). The top row lists radii (10 feet, 15 feet, 20 feet, 25 feet, and so on). The numbers in the grid are the maximum allowable loads in pounds at each combination.
To read the chart for a specific lift:
- Determine the boom length you plan to use. This depends on how high the load needs to go and how far the crane is from the placement point.
- Find that boom length in the left column.
- Determine the radius. Measure (or estimate) the horizontal distance from the crane’s center pin to where the load will hang during the critical part of the lift.
- Find that radius in the top row.
- The number at the intersection of the boom length row and the radius column is the maximum load the crane can handle at that configuration.
If the load (including the weight of rigging hardware, the hook block, and any below-the-hook equipment) is less than the chart value, the lift is within the crane’s capacity. If it exceeds the chart value, you need a shorter radius, a shorter boom, or a bigger crane.
What Most People Miss
The Chart Includes Deductions
The load chart capacity is the gross capacity at the boom tip. But the crane does not lift the load with nothing between the boom tip and the load. The hook block, the wire rope reeving, and any rigging attachments (slings, shackles, spreader bars, man baskets) all hang from the boom tip and consume part of the available capacity.
A hook block alone can weigh 500 to 2,000 pounds depending on the crane size. A set of rigging slings, shackles, and a spreader bar can add another several hundred pounds. If the chart shows 8,000 pounds of capacity at the planned radius and boom length, and the hook block and rigging weigh 1,200 pounds, the actual available capacity for the load itself is 6,800 pounds, not 8,000.
An experienced operator calculates these deductions automatically. But a contractor who does not understand them may think the crane has more margin than it does.
Radius Changes During the Lift
The radius at the start of the lift is not necessarily the radius at the end. If the crane picks a load close to the machine and then booms out to place it farther away, the radius increases during the swing. The capacity at the longer radius may be significantly less than the capacity at the pickup radius.
The critical moment is usually the placement, not the pickup, because that is where the radius is longest. The operator plans the lift based on the worst-case radius (the farthest point the load will reach), not the best-case radius (where the load starts).
Wind and Dynamic Loading
Load charts are based on static conditions: no wind, no sudden movements, and the load hanging motionless from the hook. In real operations, wind pushes on the boom and the load, dynamic forces from swinging and hoisting add momentary loads, and the crane’s structure flexes under these combined forces.
Crane manufacturers account for some of these dynamic factors in the load chart’s safety margins, but extreme wind or aggressive operation can push the crane beyond those margins even when the static load is within the chart. This is why operators reduce the working capacity in high wind, on unstable ground, or when the load is swinging.
Multiple Chart Configurations
Most cranes have more than one load chart. Common configurations include:
- Full outriggers extended. This is the highest-capacity configuration because the outriggers provide the widest base and the greatest stability.
- Partial outriggers. Some cranes can operate with outriggers partially extended, which is useful on tight sites where full extension is not possible. The load chart capacity drops significantly in this configuration.
- On rubber (no outriggers). Some cranes can make lifts without deploying outriggers, which speeds up setup but drastically reduces capacity. The “on rubber” chart is a fraction of the full-outrigger chart.
- Over the side vs. over the rear. Some cranes have different capacities depending on the direction of the lift. Lifting over the rear (where the counterweight is) typically provides the highest capacity.
Using the wrong chart for the actual crane configuration is a serious error. If the crane is set up on partial outriggers and the operator is reading the full-outrigger chart, the crane is overloaded even though the chart says it is fine.
Why Contractors Should Care
You do not need to memorize load charts or perform the calculations yourself. That is the operator’s job. But understanding how the chart works makes you a better client and a safer job site partner.
During planning: When you call a crane company to book a lift, providing the load weight, the required reach, and the lift height lets the crane company select the right machine. If you know your load weighs 6,000 pounds and needs to reach 45 feet from the crane at a height of 40 feet, the crane company can check the load chart before dispatching and confirm that the crane they are sending can handle the job. This prevents the costly scenario of a crane showing up and discovering it cannot make the lift.
During the pre-lift meeting: When the operator walks through the lift plan, you can follow the logic. If the operator says the lift is tight at the planned radius, you understand what that means and can discuss alternatives (repositioning the crane closer, using a different setup point, staging the load for a shorter reach).
When something changes: If the load turns out to be heavier than expected, or the crane cannot set up where planned and needs to work from a longer radius, you understand why the operator is concerned and can help find a solution instead of pressuring them to “just make it work.”
A crane provider that communicates openly about load charts and lift planning makes the process easier for everyone. See the types of lifts we plan and execute in our portfolio, or learn more about our team.
If you have an upcoming lift and want to talk through the load, reach, and equipment requirements, call Green Mountain Crane Service at (802) 370-5361 or reach out online.