A tower crane load chart lists the permitted lifting capacity at stated working radii for one specified crane configuration. To read it, confirm the configuration, find the radius you need, then apply the chart’s load definition and notes. The maximum tonnage on the crane’s name only applies close in. Out along the jib, the number drops.
In procurement, the chart is what ties a proposed crane to the project’s real loads and positions. The method below helps you make that comparison. Lifting on site is a different matter: it runs on the selected crane’s current manufacturer documentation and the project’s approved lifting procedures.
Confirm the Crane Configuration Before Reading Capacities
Check the manufacturer, exact model, chart number and revision. Then match jib length, reeving, operating mode and any other configuration conditions the documentation names. A chart for a different jib arrangement or rope configuration can give quite different capacities.
Reeving is how the rope parts are arranged to support the hook block, and it affects both allowable load and operating performance. If the chart has several curves or columns, work out which one applies before you read a single radius value.
Shortlisting a crane in this class? We can supply the chart for each proposed configuration of the IHURMO PT7015-10 10-ton topless tower crane with a 70 m jib or the IHURMO 12-ton flat-top tower crane with a 70 m jib. Ask for it early, because the tonnage and jib length in a model name will not tell you the capacity at your critical radius. More cranes are listed in our tower crane range.
Measure Working Radius from the Slewing Center
Working radius is the horizontal distance from the crane’s center of rotation to the vertical line of the load. It is not measured from the nearest mast face or the building edge, and it has nothing to do with hook height. If any of these terms are unfamiliar, our crane terminology guide explains them.
Mark the crane’s center on the site plan and measure to the pickup, travel and placement positions. Follow the whole route. A lift that starts comfortably inside capacity can go over it if the load line drifts outward on the way to the drop point.
On a horizontal-jib crane, moving the trolley changes the radius. On a luffing-jib crane, raising or lowering the jib changes the geometry. Use the radius and configuration definitions in the relevant manual, and keep jib length and working radius apart: they are different measurements.
Read the Radius Row and the Applicable Capacity
Find the required radius on the chart and read the capacity for the confirmed configuration. Check the units first. Tonnes, kilograms and pounds must never be mixed, and an abbreviation you cannot place should go back to the supplier as a question.
Many charts show a band of constant maximum capacity near the mast, then capacity falling off as the radius grows. Where that transition sits, and the values beyond it, are specific to each crane. One simple load-times-radius formula will not reproduce the chart.
| Working radius | Illustrative chart capacity (fictional values – not an IHURMO chart) | Interpretation |
| 20 m | 6,000 kg | Capacity at this listed radius and fictional configuration |
| 30 m | 4,000 kg | A lower capacity applies farther from the slewing center |
| 40 m | 2,500 kg | The inner-radius rating cannot be carried over |
If the required radius falls between two listed positions, follow the method the manufacturer states. Do not interpolate, round down to the shorter radius or stretch a curve past its published range unless the instructions explicitly allow it.
Apply the Chart’s Load Definition and Deductions
First, find out what the chart capacity includes. List the lifted object, slings, lifting beam, attachments and anything else hanging from the hook, then account for the hook block and other deductions exactly as instructed. Leave nothing out, and count nothing twice. Our crane rigging guide covers the rigging side of that list.
Use verified weights and keep a note of where each came from. A delivery note may give the nominal mass of a precast unit while temporary lifting fittings add to it. Settle any doubtful weights before you treat the check as finished.
A fictional example: the chart instruction says to compare an object of 2,100 kg plus 300 kg of rigging, with no further deductions. The comparison mass is 2,400 kg. Against the fictional 40 m entry in the table above, the arithmetic leaves 100 kg. That figure is not a recommended operating margin, and it is not approval to lift.
A real chart may call for different accounting and add restrictions of its own. In the United States, OSHA’s crane operation requirements cover manufacturer procedures, access to rated-capacity information and operation within rated capacity. A planning spreadsheet sits underneath those requirements, never in place of them.
Check Restrictions Beyond the Capacity Number
Read the chart notes and the operating manual for limits on wind, load area, speeds and configuration. A large wall panel can catch enough wind to cause trouble even when its mass looks fine on paper. If the chart does not cover the planned conditions, ask the manufacturer.
Check hook height and clearance as a separate exercise. A tall component and its rigging can pass the load-radius check and still hit the building on the way in. Put pickup elevation, installation elevation and overhead obstructions into the planning information.
Foundation design, ties, erection conditions and interference with other cranes or structures are separate checks too. Plenty of chart capacity is no help if the crane cannot stand or be erected where it has been drawn.
Turn the Load Chart into a Quotation Review Schedule
Make one row for each critical lift: item, verified mass, rigging, required deductions, maximum radius, hook height and the proposed chart reference. Ask the supplier to flag any lift that falls outside the quoted configuration.
This article stays with chart reading. For load and radius checks applied to a full component schedule and erection sequence, see our precast concrete crane selection guide.
If a lift does not fit, look at another configuration, a new crane position or a changed delivery point with the responsible team, then recheck every lift the change affects. Moving up to a crane with a bigger tonnage label does not, on its face, solve the problem.
Tower Crane Load Chart FAQs
Is tip capacity the same as maximum lifting capacity?
No. Tip capacity applies at the specified outer radius for the relevant configuration. Maximum lifting capacity usually applies over a shorter, more limited radius range.
Can a load-moment calculation replace the chart?
No. A simple calculation shows how radius affects capacity, but it cannot capture all the structural, mechanical and operating limits built into the manufacturer’s chart.
Is a limiter display sufficient for purchasing checks?
No. Ask for the actual chart and configuration documents. A limiter helps the operator on the day; it is no evidence that the proposed layout and lift schedule have been reviewed.
Request the Chart for the Proposed Crane Configuration
Request IHURMO tower crane load-chart information and include the site plan, proposed crane position, critical load schedule, radii and hook heights. We will tell you the chart revision, jib arrangement, reeving and equipment scope behind the quotation.
