How to read a boom truck load chart

R 03 mWhat a load chart must show

Alberta, Manitoba and Ontario name the load chart in their regulations. Alberta requires a mobile crane or boom truck to carry load charts at all times showing rated capacity at all permitted boom angles and radii, in s.63(1)¹. Manitoba sets the same requirement in s.23.9(2)². Ontario requires a load rating chart readable at the controls, or a model and serial plate linked to that crane's charts, with chart access at all times for a remote-control operator, in s.151(3)³.

In Alberta, an operator must be able to show knowledge of load charts and the hoisting signal code at the employer's request, under s.64¹. Certificates by province are in operator certification.

Read the metric figures: CSA Z150:20 makes SI values the units of record, with values in parentheses for information only, in clause 1.7⁴.

R 06 mRadius, not boom length

A chart is read by radius. IHSA defines load radius as the horizontal distance from the crane's centre of rotation to the load hook while the boom is loaded, and notes that radius grows under load as the boom and machine deflect⁵. Boom length picks the column; radius picks the row.

For a straight boom, radius is about the boom length times the cosine of the boom angle, plus the boom foot's offset from the centre of rotation; tip height is about the length times the sine of the angle, plus the foot pin height. Deflection makes the loaded radius larger⁵.

Booming down from 60° to 30° takes the hook from about 7.9 m to 13.4 m, and the chart figure falls with it. So:

• Use the largest radius in the lift: pick, set, or anywhere the load passes on the way.
• Measure on site, from the centre of rotation to where the hook will hang over the load's centre. A drawing dimension to a building face is not a radius.
• Read the longer row when your radius falls between rows. Do not interpolate upward.

The boom reach calculator works this geometry both ways.

R 09 mStructural limits and stability limits

Every chart figure is capped by the strength of the crane's parts or by the truck's resistance to tipping. CSA Z150:20 keeps them apart: ratings governed by stability under clause 4.1.1, ratings governed by structural competence under clause 4.1.2⁶.

Stability. CSA Z150:20 Table 1 caps a stability-governed rating at a share of the tipping load, the load at which the crane would start to tip:

The 2026 edition, CSA Z150:26, was not checked for this table⁸; provinces adopt their own editions (inspection rules). The gap between 85% and tipping is not spare capacity. Queensland's mobile crane code, a non-Canadian reference, says chart capacities must never be exceeded outside controlled testing⁹.

Structure. A structural figure is set by the strength of the boom and its components, not by balance. A truck can feel planted while a structural figure is exceeded, so the feel of the machine says nothing about it. Some charts mark which entries are structural; if yours does not, ask the supplier. No Canadian regulator text we found says where one limit gives way to the other; the last section shows one published chart.

R 12 mWhat you subtract before reading the chart

Everything hanging from the boom tip counts against the chart figure. IHSA states that a hoist's rated load does not account for hook blocks, hooks, slings or equalizer beams, so their combined weight is added to the load⁵. U.S. OSHA's definition of load, a non-Canadian reference, also includes the load block, ropes, slings and shackles¹⁰.

Queensland's mobile crane code, a non-Canadian reference, gives the arithmetic: a chart rating of 20 t with 1 t of hook block and lifting gear leaves 19 t for the load⁹. It also says an attached fly jib is deducted when lifting on the main hook unless the chart allows for it, because main-boom figures generally assume the jib is removed, again a non-Canadian reference⁹.

The load's weight has to be known, not guessed. WorkSafeBC requires each load's weight to be determined and communicated to the operator and rigger; where it cannot be determined accurately, the crane must have a load weight indicator or overload prevention system, under s.14.36¹¹. Alberta requires the operator, the rigger and the person in charge of a lift to be given the information to determine the weight readily and accurately, under s.68¹.

The chart's notes say what is already included. Slings and spreaders: see sling angles and rigging.

R 15 mOutriggers, level ground and quadrants

Outriggers. IHSA says full "on outriggers" ratings apply only when all outrigger beams are fully extended and all tires are clear of the ground; partial extension needs its own chart, or the "on tires" rating applies⁵. Alberta requires a boom truck's outriggers to be extended and supported by solid footings before use, under s.90¹. On a narrow street, ask before booking whether the chart has a partial-extension column, and plan on that column.

Level, firm ground. IHSA states that chart ratings apply only on ground firm enough to keep the crane level, with timber or steel mats on soft ground or backfill⁵. A small tilt costs a lot. In IHSA's example table for one crane:

One crane's figures, not a rule, but the long boom lost three times as much at 1°. Check level once the outriggers carry the truck.

Quadrants. IHSA notes that capacity is normally greatest over the rear, less over the side, and may be nil over the front, depending on the machine's quadrant chart⁵. If the load swings from the rear to the side, the side figure governs. Ask the supplier for the chart capacity at your radius, over the quadrant you will use. Pads and ground pressure: outriggers and ground bearing pressure.

R 18 mDuty cycles and working margins

A chart figure is a limit, not a target. Two reductions and two regulatory lines apply:

• Duty-cycle work. IHSA notes manufacturers typically require ratings to be reduced, usually by 20%, for duty-cycle work such as concrete placing, or supply a separate chart⁵.
• Working margin. IHSA recommends a crane with at least a 5% working margin over the capacity each lift requires⁵.
• Alberta's 75% line. A lift calculation must be completed for any lift exceeding 75% of a crane's rated capacity, under s.68.1¹.
• BC's critical lift. A mobile crane or boom truck lift over 90% of rated capacity at more than 50% of maximum permitted radius is a critical lift, as is any lift over or between energized high-voltage conductors¹¹.

Example: from the load to the chart figure to ask for

1. Start from the worksheet's 2,115 kg on the hook (example figures) and add IHSA's 5% margin: 2,115 × 1.05 = about 2,221 kg.
2. For repetitive work where the manufacturer calls for a 20% reduction, the chart needs 2,221 ÷ 0.80 = about 2,776 kg at your radius.
3. Check Alberta's line against the chart you get. At 3,000 kg on the chart, the lift uses about 70.5%. At 2,600 kg, it uses about 81%, and a lift calculation comes first.

The size estimator runs these steps, and lift planning covers who prepares the calculation.

R 21 mIndicators and their errors

Indicators help the operator stay on the chart; they do not replace it.

• Angle and radius. WorkSafeBC requires a boom angle indicator readable at the control station, and a boom extension or radius indicator, wherever rated capacity depends on them, under ss.14.7 and 14.8¹¹. IHSA cautions that boom angle indicators can be off by as much as 2 degrees and should not be relied on for critical lifts; a measured radius is preferred⁵.
• Load weight and overload. In BC, a mobile crane or boom truck rated 10 tonnes (11 tons) or more needs a load weight indicator, or a system that stops lifting beyond rated capacity, meeting SAE J376, under s.14.64¹¹. Quebec's construction code requires overload prevention on mobile cranes, with a load limiter or load moment controller meeting SAE J159 on cranes made from January 1, 2005¹².
• Load moment. U.S. OSHA describes a load moment indicator as sensing the overturning moment and showing the percentage of capacity in use, a non-Canadian reference¹⁰. Check that it is set for the outriggers, boom length and attachments in use that day.

As arithmetic, a 2° error on a 15 m boom near 60° moves the radius about 0.45 m: easily a whole row of the chart.

R 24 mA worked example from a published chart

We found no Canadian regulator that publishes a sample chart. NT WorkSafe, in Australia's Northern Territory, publishes an example knuckle-boom chart, used here as a non-Canadian reference: one example, not a typical truck.

In that non-Canadian reference, capacity falls from 4,550 kg at 2.89 m to 730 kg at 12.55 m¹³. Knuckle booms are rated in metre-tonnes, the maximum load times its radius, which on that non-Canadian reference chart is 2.89 m × 4.55 t = 13.145 metre-tonnes¹³. Multiply each row's load by its radius and, in this non-Canadian reference, the product stays near 13.0 to 13.5 tonne-metres out to 8.33 m, then falls to about 9.2 tonne-metres at 12.55 m (derived)¹³.

Example: a 1,000 kg load plus 60 kg of hook and slings: 1,060 kg on the hook.

• At 2.89 m it uses 1,060 ÷ 4,550 = about 23% of the chart figure.
• At 12.55 m it cannot be made: 1,060 kg is more than 730 kg.
• In between, shortcuts fail. If 13.0 tonne-metres held all the way out, the load could go to 13.0 ÷ 1.06 = about 12.3 m. At the long end the moment is nearer 9.2, and 9.2 ÷ 1.06 = about 8.7 m. The real limit lies between the two; only the chart row says where.

With IHSA's 5% margin, look for about 1,113 kg. On any chart, read the row at the longest radius, for the set-up you will actually use. A truck's headline rating is the best case on its chart, at short radius; it says little about what it lifts at 10 m.