When selecting a crane, many people start with one question: “How heavy is the load?” This information is necessary, but it is not enough. A 5-ton machine positioned close to the crane may require a completely different lifting plan from another 5-ton machine located 12 meters inside a factory.
The difference comes from the working radius, boom length, outrigger configuration, counterweight, and technical limits of each crane model. Therefore, labels such as “25-ton crane,” “50-ton crane,” or “100-ton crane” should never be understood as a fixed lifting capacity available at every position.
The correct way to understand how to read a crane load chart is to identify the actual working conditions first, then refer to the correct load chart for the exact crane model and configuration. The operator or lift planner should not start by choosing an attractive capacity figure from the chart and then try to make the job fit that number.
What Is a Crane Load Chart?
A crane load chart is a manufacturer-issued technical document showing the rated lifting capacity of a specific crane model under defined working conditions. The values are commonly associated with working radius, boom length, boom configuration, outrigger position, counterweight, and working area.
In simple terms, a load chart answers one key question: At the current radius and crane configuration, what is the maximum rated load this crane can lift?
A load chart is not a universal table that can be applied to every crane with the same nominal capacity. Two cranes both marketed as 25-ton cranes may have completely different boom systems, counterweights, chassis designs, and rated capacities at the same radius.
One crane model may also have several load charts. One chart may apply when the outriggers are fully extended, while another may apply to a different outrigger position or boom configuration. For this reason, the first step is always to confirm the correct crane, correct configuration, and correct operating conditions.
Key Parameters to Understand Before Reading a Load Chart
The difficult part of reading a load chart is usually not finding a number inside a table. The real challenge is identifying the correct input conditions. Confusing working radius, boom length, or outrigger position can lead to selecting the wrong section of the chart.
| Parameter | Meaning When Reading a Load Chart | Common Mistake |
|---|---|---|
| Working radius | Horizontal distance from the crane’s center of rotation to the vertical line through the load, according to the manufacturer’s definition | Measuring from the side of the truck or confusing it with boom length |
| Boom length | Length of the boom used for the lift | Checking only the radius and ignoring the boom-length column |
| Boom angle | Geometric parameter related to boom position and working radius | Estimating capacity from boom angle instead of using the proper chart |
| Outrigger position | Stability condition associated with the selected chart | Using a fully extended outrigger chart when the outriggers are not fully deployed |
| Counterweight | Counterweight configuration required for the chart | Failing to confirm the actual counterweight installed on the crane |
| Rated lifting capacity | Permitted load for the specified conditions | Assuming this number always equals the weight of the cargo itself |
Working Radius Is Not the Same as Boom Length
The working radius is generally the horizontal distance from the crane’s center of rotation to the vertical line passing through the suspended load, according to the crane manufacturer’s definition.
This is one of the most commonly misunderstood parameters. If the boom is 20 meters long, the working radius is not automatically 20 meters. Because the boom is raised at an angle, its horizontal reach is usually shorter than its actual length.
During site surveys, the distance should not simply be measured from the truck body, tire, or outrigger pad to the load. The correct reference point must follow the manufacturer’s technical documentation.
Boom Length Determines Which Chart Column to Use
Boom length describes how far the main boom has been extended. On many load charts, separate columns represent specific boom lengths or boom-length ranges.
At the same working radius, different boom lengths may not provide the same rated lifting capacity. When the crane must reach over a roof, wall, pipe rack, or machinery, a longer boom may be required even if the horizontal distance to the load does not change significantly.
Boom Angle Describes the Geometry of the Lift
Boom angle describes the position of the boom relative to the reference plane defined by the manufacturer. Boom angle, boom length, and working radius are geometrically related, but one parameter should not be used to guess another when the manufacturer requires direct chart reference.
Some load charts display boom angle clearly, while others focus mainly on working radius and boom length. The correct reading method depends on the chart design provided for the specific crane model.
Outrigger Position and Counterweight Must Match the Selected Chart
Lifting capacity does not depend only on the boom. Outrigger position and counterweight configuration can also change the crane’s rated capacity.
For example, a lifting plan may assume that the outriggers can be fully extended. Once the crane arrives on site, however, a drainage channel, wall, machine, or other obstacle may prevent full deployment. If the actual outrigger configuration changes, the operator must not continue using capacity values from the fully extended chart.
This is a common real-world situation: the lifting plan may appear correct on paper, but a change in crane positioning can require a different load chart.
The Capacity Shown in the Chart May Not Equal the Cargo Weight
The capacity shown in a load chart must be interpreted according to the manufacturer’s definition. Depending on the crane and chart, the weight of the hook block, slings, shackles, lifting beam, and other below-the-hook equipment may need to be included in the total suspended load or deducted from the rated capacity.
Therefore, if a chart shows a 6-ton capacity, it does not automatically mean that a 6-ton piece of equipment can be attached to the hook. The notes accompanying the load chart must be checked first.
How to Read a Crane Load Chart Step by Step
A practical method is to work from the jobsite conditions toward the crane configuration: identify the load and its position, determine the radius, select the required boom configuration, choose the correct chart, and only then read the allowable lifting capacity.
Confirm the Exact Crane Model and Load Chart
Verify the crane model, version, and corresponding technical documentation. If several charts are provided, read the headings and notes carefully to determine whether the chart applies to the main boom, jib, a certain counterweight configuration, or a specific outrigger position.
Do not use the chart from a “similar” crane model for estimation. Two cranes with the same nominal capacity do not necessarily have the same lifting performance at each radius.
Determine Crane Position and the Most Critical Radius
Do not measure only the radius at the initial pick point. The entire load path from the pick position to the final placement position should be considered.
For example, a machine may initially be lifted at a radius of only 6 meters, but after the crane slews toward the side of the building, the load may move to a radius of 9 meters. Evaluating only the 6-meter position would not represent the entire lifting condition.
For many lifts, the largest radius reached during load movement is one of the most important conditions to evaluate.
Determine the Required Boom Length
After determining the working radius, identify the boom length required to achieve the necessary lifting height and clear surrounding obstacles. A load may not be very far from the crane horizontally, but a roof or structural obstruction may require a much longer boom.
Boom length should not be selected based only on horizontal distance. The required lifting height, final placement height, building structure, and necessary clearances all influence the boom configuration.
Select the Correct Row and Column on the Load Chart
On a typical tabular load chart, one axis may represent working radius while another represents boom length. Locate the row corresponding to the actual working radius, then find the column corresponding to the boom length being used.
The value at the intersection represents the rated lifting capacity for that combination of conditions, provided all other requirements of the chart are satisfied.
If the actual working radius does not exactly match a value shown in the chart, do not interpolate capacity based on personal judgment. Follow the manufacturer’s instructions.
Compare Rated Capacity with the Total Suspended Load
Once the chart capacity has been identified, compare it with the actual total suspended load. In addition to the cargo itself, check whether the manufacturer requires the hook block, slings, lifting beam, shackles, and other rigging components to be included.
This prevents a common mistake: a customer may report that a machine weighs 5 tons, but the lifting arrangement also uses a hook block, slings, and a spreader beam. If those components are included in the suspended load calculation, the crane must handle more than the 5-ton machine alone.
Read All Notes Before Making a Decision
Many critical conditions are written below or beside the table rather than inside the capacity cells. These may include requirements related to operating area, outrigger position, counterweight, rope configuration, number of rope parts, jib use, or other limitations.
Reading the correct capacity cell while ignoring the chart notes can still lead to an incorrect conclusion. A load chart must be treated as a complete technical document, not just a table of numbers.
Example of Reading a Crane Load Chart
The following figures are hypothetical and provided only to explain the reading process. They do not represent a specific crane model and must not be used for an actual lifting operation.
Assume a machine weighs 4.8 tons. After the site survey, the crane cannot be positioned close to the building, so the maximum working radius is 8 meters. The planned boom length is 18 meters.
Assume the relevant load chart shows a rated lifting capacity of 6.0 tons at an 8-meter working radius and an 18-meter boom length.
Now assume the lifting equipment that must be included in the suspended load consists of a 250 kg hook block, 80 kg of slings, and a 120 kg lifting beam. The total suspended load would be approximately:
4.8 tons + 0.25 tons + 0.08 tons + 0.12 tons = 5.25 tons.
For this simplified example, 5.25 tons is below the 6.0-ton rated capacity. However, this does not mean the lift is automatically safe or ready to proceed. Ground conditions, outrigger setup, operating area, environmental conditions, manufacturer limitations, and the overall lifting plan must still be checked.
This example shows why crane selection should not be based on the simple idea that “a 4.8-ton load only needs a crane rated above 4.8 tons.” The suspended load, radius, and actual crane configuration must be evaluated together.
Why a 25-Ton Crane Cannot Always Lift 25 Tons
A 25-ton crane does not mean the crane can lift 25 tons at every working radius. The nominal capacity is available only under specific conditions defined by the manufacturer. As the load moves farther from the crane’s center of rotation, the permitted lifting capacity generally decreases.
Consider two identical 5-ton machines. The first is positioned close to the crane. The second is located behind a wall, forcing the crane to remain farther away. Although the loads weigh the same, the second lift creates a larger working radius and may require a crane with substantially greater capacity.
This is why an experienced lifting team cannot accurately answer “What size crane is needed for a 5-ton load?” without knowing the crane position, radius, lifting height, and surrounding obstacles.
How Does Working Radius Affect Lifting Capacity?
As the horizontal distance between the crane’s center of rotation and the load increases, the load moment acting on the crane also increases. As a result, allowable lifting capacity generally decreases as working radius increases.
However, this principle should not be turned into a simple rule such as “double the radius and the capacity is cut in half.” Actual crane capacity depends on the specific crane design, boom configuration, structural limits, and stability limits. The correct value must always come from the manufacturer’s load chart.
Some charts may also use symbols, shaded areas, or boundary lines to distinguish structural limits from stability limits. These conventions vary between manufacturers, so markings from one crane model should not be assumed to mean the same thing on another model.
Common Mistakes When Reading a Crane Load Chart
Most errors do not come from complicated calculations. They usually result from misunderstanding the input conditions or ignoring restrictions stated in the manufacturer’s documentation.
Selecting a Crane Only by Nominal Capacity
A 10-ton load does not automatically mean that a 10-ton crane is suitable. If the load must be handled at a larger radius, the crane may no longer have 10 tons of available lifting capacity.
Measuring Radius from the Wrong Reference Point
Measuring from the edge of the truck, tires, or outrigger pads and using that distance directly in the load chart can produce an incorrect result. The radius must be determined using the reference point specified by the crane manufacturer.
Checking Only the Radius at the Pick Point
As the crane slews and the load moves toward its final position, the working radius can change. A lift should not be evaluated only at the initial pick point if the load will later move to a larger radius.
Using the Wrong Outrigger Configuration
This is a serious error because the crane itself may look unchanged while its stability condition has changed. Each load chart must be used only for the outrigger configuration specified by the manufacturer.
Ignoring Rigging Weight
Hook blocks, slings, shackles, and lifting beams all have weight. How these components are included in the total suspended load must follow the manufacturer’s instructions and the lifting plan.
Ignoring Manufacturer Notes
A capacity value is valid only when all chart conditions are satisfied. Important limitations may be stated in the notes rather than in the main table.
What Is the Difference Between a Load Chart and LMI?
A load chart and a Load Moment Indicator (LMI) are related, but they are not the same thing.
The load chart is technical documentation showing rated capacity for different crane configurations. The LMI is an electronic system that helps the operator monitor crane operating conditions based on sensor data and equipment parameters.
An LMI may provide warnings as the crane approaches certain operating limits, but it does not eliminate the need to understand the load chart, crane configuration, or manufacturer restrictions.
In short: the load chart defines rated limits for a configuration, while the LMI helps monitor the crane during operation.
Why Site Survey Data Is Critical for Reading a Load Chart Correctly
A load chart may be read correctly, but the lifting plan can still be wrong if the site survey data is inaccurate. This often happens when crane selection is based only on photographs or preliminary measurements.
For example, a customer may measure 6 meters from the load to the factory entrance and assume that the working radius will be about 6 meters. Once the crane arrives, additional space is required to deploy the outriggers, forcing the crane’s center of rotation several meters farther away. The actual working radius may therefore be significantly greater than the original estimate.
A proper site survey should confirm the load weight and dimensions, pick and placement positions, available outrigger space, ground conditions, lifting height, overhead obstacles, crane access, and the load’s travel path.
These details help ensure that the crane configuration used to read the load chart matches the conditions that will actually exist during the lift.
When Should a Lift Not Be Decided from the Load Chart Alone?
Understanding the load chart helps a lift planner or operator evaluate crane capacity, but the chart does not replace the complete lifting-planning process.
Extra caution is required when the load is close to the crane’s rated limit, the load weight or center of gravity is uncertain, the crane must operate on weak ground, the working radius is large, overhead power lines or structures are present, special lifting beams or configurations are required, or the load is particularly valuable or critical.
In these situations, crane capacity must be considered together with site conditions, applicable lifting safety requirements, and the manufacturer’s official instructions.
It is also important not to take the difference between the chart capacity and the actual load and automatically call it a “safety factor” unless this is specifically defined by the manufacturer or lifting procedure. Load charts are already developed according to specific design and regulatory criteria, so their limits should not be reinterpreted based on personal judgment.
What Information Should Be Prepared Before a Crane Site Survey?
Customers do not need to calculate every technical parameter themselves. The most useful approach is to provide accurate site and load information so that the crane team can determine the correct equipment and lifting configuration.
- Load weight or documents showing the confirmed weight.
- Overall dimensions of the load.
- Photos of the proposed crane setup area.
- Photos or video showing access from the entrance to the lifting location.
- Approximate distance between the crane position and the load.
- Pick height and final placement height.
- Obstacles such as roofs, power lines, pipework, walls, or machinery.
- Available space for outrigger deployment.
- Ground condition at the crane setup area.
This information allows the lifting team to determine crane position, working radius, boom configuration, and suitable equipment before checking the load chart in detail.
Frequently Asked Questions About Crane Load Charts
Below are some of the most common questions asked by people learning how to read crane load charts and understand actual lifting capacity.
What is a crane load chart used for?
A crane load chart shows the rated lifting capacity of a specific crane model under defined conditions such as working radius, boom length, outrigger position, and counterweight configuration. It is used to check whether the planned crane setup can handle the intended load.
How do you read a crane load chart?
First confirm the exact crane model and configuration. Then determine the working radius and boom length. Find the corresponding row and column in the load chart, read the rated capacity at their intersection, and review all manufacturer notes before comparing it with the total suspended load.
Can a 25-ton crane lift 25 tons at every position?
No. Nominal capacity is available only under specific operating conditions. As working radius increases or the crane configuration changes, the allowable lifting capacity generally decreases. Actual capacity must be taken from the correct load chart.
From where is crane working radius measured?
Working radius is generally measured horizontally from the crane’s center of rotation to the vertical line through the load, according to the manufacturer’s definition. It should not automatically be measured from the truck body, tire, or outrigger pad.
Are boom length and working radius the same?
No. Boom length is the actual length of the boom in use, while working radius is the horizontal distance from the crane’s center of rotation to the load. They are related geometrically, but they are not interchangeable.
Why does lifting capacity decrease as working radius increases?
As the load moves farther from the crane’s center of rotation, the load moment increases. This generally reduces allowable lifting capacity. The exact reduction depends on the crane model and must be taken from the manufacturer’s load chart.
Can I use the load chart of another crane with the same nominal capacity?
No. Two cranes may both be rated at 25 tons or 50 tons but have different boom systems, counterweights, structures, and rated capacities. The correct chart must match the actual crane model and configuration.
Can an LMI replace the crane load chart?
No. An LMI helps monitor operating conditions and provide warnings, while the load chart defines rated lifting capacity for specific crane configurations. The operator still needs to understand the chart and manufacturer limitations.
Should hook block and sling weight be included when checking crane capacity?
The manufacturer’s documentation must be checked. Depending on the chart, hook blocks, slings, lifting beams, shackles, and other lifting accessories may need to be included in the total suspended load or deducted from the rated capacity.
Conclusion
The basic method for reading a crane load chart can be summarized as follows: correct crane model, correct configuration, correct working radius, correct boom length, correct capacity value, and correct operating conditions.
The most important point is that a crane should not be selected only by cargo weight or nominal crane capacity. A relatively light load located deep inside a factory may be more demanding than a heavier load positioned next to the crane because the required working radius and boom configuration are completely different.
A load chart converts real site conditions into technical lifting limits that can be checked. However, it is only one part of a complete lifting plan. For complex lifts or loads close to the crane’s rated limits, the site should be reviewed by qualified personnel, the manufacturer’s official documentation should be checked, and all lifting conditions should be evaluated before work begins.
