A crane load chart tells you the heaviest load a crane is rated to lift at a given working radius, boom length and boom angle, in the set-up the chart assumes. The tonnage in the model name is only the top line of that chart. Our 5-ton SQ5SA4 telescopic crane lifts its full 5,000 kg only at a 2.2 m radius, with the shortest 4.2 m boom raised to 50°. At its full 11.8 m reach the chart allows 600 kg.
This guide shows how to read a crane load chart step by step, using the real charts our technical department draws for three current BOB-LIFT truck mounted crane models: a 5-ton telescopic crane, a 10-ton knuckle boom crane and a 20-ton telescopic crane. Each example ends with a clear yes or no, and every figure was checked by Achord Chan, Product Operations Director, against the original BOB-LIFT technical drawings.
Key takeaways
- Rated capacity depends on radius first. On the three charts below, capacity at full reach is 7.5% to 12% of the headline tonnage.
- Measure radius horizontally from the slewing centre to the hook, at both pick-up and landing, and use the larger one.
- When your radius falls between two chart values, use the capacity at the larger radius. Do not average the two.
- Count the hook block, slings and lifting accessories as part of the load unless the chart says they are already deducted.
- At the same radius, a longer boom set-up usually lifts less, so choose the shortest boom that reaches.
What does a crane load chart tell you?
A load chart lists the rated capacity of the crane at each working radius, for each boom set-up the manufacturer approves. Rated capacity is the most the crane may lift in that position. It is set by the weaker of two limits: the strength of the boom and structure, and the stability of the crane and truck on their outriggers.
Both limits shrink as the load moves out. The force that tips the crane grows with the load multiplied by its distance from the slewing centre. That product is the crane’s lifting moment, given in tonne-metres (t·m). The SQ5SA4 is rated at 12.5 t·m (5,000 kg × 2.5 m), yet its table caps the 5,000 kg rating at a 2.2 m radius. The SQ20SA5 is rated at 50 t·m (20,000 kg × 2.5 m), and its table gives 20,000 kg at 2.0 m. Our article on the lifting moment of a crane explains the idea in more depth.
Moment alone does not give you a safe capacity. The chart is worked out for each boom length and angle, so it does not follow a simple moment ÷ radius curve. Divide the SQ20SA5’s 50 t·m by 22 m and you get about 2,270 kg, yet the chart allows 1,500 kg at 22 m, because the long, extended boom carries its own weight further out. Always read the chart rather than calculating from the moment. Our guide to ways to calculate crane capacity covers the rough estimates and where they stop working.
The parts of a truck crane load chart
Most truck mounted crane charts combine a range diagram and a set of capacity values. Here is the chart for our SQ10ZA6 10-ton knuckle boom truck mounted crane, with its four main parts numbered.
1. Working radius
The horizontal axis is the working radius in metres. Radius is the horizontal distance from the crane’s slewing centre (the centre of rotation) to the hook line. It is not the boom length, and it is not the distance from the truck’s side.
2. Lifting height
The vertical axis is the height of the hook above the ground reference shown on the drawing. Use it to check that the hook can clear a wall, a truck body or a roof edge at the radius you need. The SQ10ZA6 reaches about 17 m with the boom near its 84° maximum.
3. Boom angle lines
The straight lines fanning out from the base mark the boom angle, from 0° (level) to the maximum. The curved lines show how far the hook travels as the boom raises with each extension pushed out. Where a curve meets an angle line, you can read the radius and height for that position.
4. Capacity boxes
Each box gives three numbers stacked: the radius in millimetres, the rated capacity in kilograms and the same capacity in pounds. On the SQ10ZA6 they run from 2,000 mm / 10,000 kg to 14,680 mm / 1,150 kg. Read the kilogram line. The pound line is the same limit, rounded, for readers who work in imperial units.
Every chart also rests on conditions that are not drawn as numbers: outriggers extended as the manufacturer specifies, the truck level and the ground firm enough to carry the outrigger loads. If any of those is not true on site, the numbers on the chart do not apply.
Telescopic vs knuckle boom load charts
Telescopic and knuckle boom cranes are read the same way, by radius, but their charts are laid out differently. If you are still choosing between the two types, start with telescopic vs knuckle boom cranes.
| Chart feature | Telescopic boom (SQ5SA4, SQ20SA5) | Knuckle boom (SQ10ZA6) |
|---|---|---|
| Main table | Boom length across the top, boom angle down the side | Capacity boxes along the horizontal reach |
| Each cell or box | Working radius / capacity for that length and angle | Radius, kg and lbs at each extension point |
| Range diagram | Hook path for each boom length | Hook path for each extension, with angle lines |
| What you choose | Boom length and angle | How far the extensions are pushed out |
On a telescopic chart, boom length and radius are different numbers. The SQ20SA5’s 6.8 m boom gives a 6.3 m radius when level, because the boom’s root hinge does not sit on the slewing centre, and radius is always measured from the slewing centre. Read the radius in the cell, not the boom length in the header.
How to read a crane load chart in 6 steps
Work through these six steps for every lift, in this order. If one step fails, change the set-up and read the chart again.
- Weigh the whole load. Add the hook block, slings, shackles, spreader bar and any other lifting accessory to the weight of the item. Hook blocks are usually marked with their weight.
- Measure the radius. Measure horizontally from the slewing centre to where the hook will hang, at pick-up and at landing. Use the larger of the two.
- Pick the boom set-up. Find the boom length or extension and the angle that reach that radius and clear any obstacle at the height you need.
- Read the capacity. Find your radius on the chart. If it falls between two listed radii, use the value at the larger radius. Do not average the two values.
- Compare with margin. The total from step 1 must not exceed the capacity from step 4. If it is close, plan for wind, swing and an imprecise load weight.
- Check the conditions. Outriggers out as the chart assumes, truck level, ground firm, and wind within the limits in the operator manual.
Example 1: a 5-ton telescopic crane (SQ5SA4)
The job: lift a 1,500 kg pallet of blocks off the truck bed and land it 6.0 m from the slewing centre. The slings and hook add an estimated 50 kg, so the total load is 1,550 kg. Here is the boom table from the SQ5SA4 5-ton telescopic boom truck mounted crane drawing.
With the 6.8 m boom at 20°, the chart gives exactly 6.0 m / 1,740 kg. The total load of 1,550 kg is below 1,740 kg, so the lift is within the chart, with 190 kg to spare.
Now suppose a wall forces you to use the 9.4 m boom to get over it. At 40° that boom puts the hook at 6.7 m and allows only 1,300 kg. The same pallet is now too heavy. To use the longer boom you would have to raise it to 50°, where the radius drops to 5.5 m and the capacity rises to 1,580 kg, and only if the landing spot can move to 5.5 m.
The lesson: near the same radius, a longer boom lifts less, because more of the crane’s strength goes into holding up its own boom. Use the shortest boom that reaches.
Example 2: a 10-ton knuckle boom crane load chart (SQ10ZA6)
The job: lift a 2,000 kg steel frame from close to the truck and land it 9.0 m from the slewing centre. The landing radius is the larger, so it governs. With 60 kg of hook and slings, the total is 2,060 kg. The SQ10ZA6 chart lists 2,280 kg at 8.51 m and 1,800 kg at 10.56 m. There is no 9.0 m value.
Because 9.0 m lies beyond 8.51 m, you must read the 10.56 m value: 1,800 kg. The 2,060 kg load is too heavy. Averaging 2,280 and 1,800 would suggest about 2,170 kg and a lift that looks fine on paper. That is exactly the mistake the rule exists to prevent.
The fix is to move the truck. If the driver can set up so the landing point is 8.5 m or less from the slewing centre, the chart value is 2,280 kg and the lift is within the chart. For more on how the folding boom changes capacity along its reach, see our article on knuckle boom crane lifting capacity.
Example 3: a 20-ton telescopic crane (SQ20SA5)
The SQ20SA5 20-ton telescopic boom truck mounted crane lifts its full 20,000 kg only with the 6.8 m boom raised to 70°, at a 2.0 m radius. The job here: lift a 4,000 kg bundle of steel beams to a point 12 m from the slewing centre, with 80 kg of rigging, for a total of 4,080 kg.
Two set-ups reach 12 m or a little beyond:
| Boom set-up | Radius on chart | Rated capacity | 4,080 kg load |
|---|---|---|---|
| 14.8 m boom at 30° | 12.2 m | 5,640 kg | Within the chart |
| 18.8 m boom at 40° | 13.5 m | 3,840 kg | Too heavy |
The 14.8 m boom at 30° covers 12.2 m, slightly more than you need, so its 5,640 kg rating applies with room to spare. To reach past 12 m the 18.8 m boom must come down to 40°, where it allows only 3,840 kg, less than the 4,080 kg total. As in Example 1, the shorter boom wins.
Note that the 20-ton crane still lifts 1,500 kg at 22 m, more than the 10-ton SQ10ZA6 lifts at 14.68 m. If your work is mostly light loads far from the truck, compare reach and capacity at your radius, not the tonnage in the name. Our guide to selecting truck mounted crane tonnage walks through that choice.
Common load chart mistakes
- Treating the tonnage as the working capacity. A 10-ton crane is a 10-ton crane only at about 2 m.
- Leaving out the rigging. Hook blocks, slings, shackles and spreader bars add weight that the chart counts as load unless it says otherwise.
- Measuring radius from the wrong point. Measure from the slewing centre, not the boom tip, the truck’s side or the outrigger.
- Reading between the lines. If your radius is not listed, use the next larger radius on the chart.
- Using a chart for different conditions. A chart drawn for fully extended outriggers does not apply when one outrigger is short or on soft ground.
- Using the wrong model’s chart. Variants of the same tonnage, such as marine versions and cranes with a fly jib, have their own charts. Check the model code on the drawing.
Mounting matters too. The chart assumes the crane is fitted to a chassis and subframe that can carry it. Our guide to truck mounted crane installation covers what the truck needs.
Matching a load chart to your job
If you are choosing a crane, start from your heaviest regular lift and the radius it happens at, not from the tonnage. Send us four numbers: the load weight, the working radius, the lifting height and your truck chassis model. Our engineers will check them against the charts of our telescopic boom truck mounted cranes and knuckle boom truck mounted cranes and send you the matching load chart. You can reach us through our contact page.
Every BOB-LIFT product page shows the dimension drawing and load chart for that model.
Frequently asked questions
Does the load chart include the hook and slings?
Treat the hook block, slings and other lifting accessories as part of the load unless the chart or its notes state that they are already deducted. If you are not sure, ask the manufacturer for the chart notes before you lift.
Can I interpolate between two radii on a load chart?
No, unless the manufacturer’s instructions allow it. Use the capacity at the next larger radius listed. On the SQ10ZA6, a 9.0 m lift is rated at the 10.56 m value of 1,800 kg, not at a figure between 1,800 and 2,280 kg.
Why does a 10-ton crane lift only 1,150 kg at full reach?
The 10 tonnes apply at a 2.0 m radius. At 14.68 m the load is more than seven times further out, so the tipping moment is far higher, and the crane must also hold up its fully extended boom.
Where should the load chart be kept?
With the crane, where the operator can see it. In the United States, OSHA rule 29 CFR 1926.1417(c) requires the rated capacities (load charts) to be readily available in the cab for the operator, and 29 CFR 1926.1433(d) adds what that information must include for equipment made after November 8, 2010. Articulating boom cranes are also covered by the voluntary ASME B30.22 standard. Check the rules where you work. This guide explains how charts are read; every real lift must be planned by a competent person using the chart supplied with your crane.
How do I convert the chart from kg to lbs?
Multiply kilograms by 2.2046. Our charts already print a pounds line under the kilograms, for example 10,000 kg / 22,000 lbs on the SQ10ZA6. The pound values are rounded, so use the kilogram figure when a lift is close to the limit.
Crane load chart checklist
- Read capacity at your working radius, not from the model name.
- Count everything below the boom tip as load, including the rigging.
- Use the next larger radius on the chart, and choose the shortest boom that reaches.
- Only use a chart in the conditions it was drawn for.
Load charts for every model are on our product pages, starting with the truck mounted crane range. If a lift is close to the limit, send us the numbers and we will read the chart with you.
