What is a Load Chart (Duty Chart)?
The foundation of every safe crane lift
A Load Chart (also called a Duty Chart or Radius Chart) is a manufacturer-produced table or graph that defines the maximum safe working load (SWL) a crane can lift at a specified radius (horizontal distance) from the crane centre, for a given boom length, boom angle, and configuration (outriggers in/out, counterweight, reeving).
Gross vs. Net Capacity
Chart values are gross capacity — they include the weight of the hook block, slings, and lifting accessories. You must deduct rigging weight to find the true net load you can lift.
Radius is Measured Horizontally
Radius = horizontal distance from the crane centreline (slewing centre) to the centre of the load. It is NOT the boom length projected along the ground.
Reeving (Parts of Line)
More parts of line = lower line pull on each rope, but slower hook speed. Charts may specify minimum reeving required to reach a particular rated capacity.
Outrigger Configuration
Most mobile cranes have separate columns for outriggers fully extended vs. on rubber (tyres). On-rubber capacities are significantly lower.
Slew Zone Restrictions
Some cranes have reduced capacity over the front or rear. Check the chart's slew zone diagram — working over the side may allow more or less capacity.
Boom Length Steps
Charts list discrete boom lengths (e.g., 10.4 m, 14.2 m, 20 m…). If your required boom is between two chart columns, you must use the longer boom column (lower capacity).
How to Read a Load Chart – Step by Step
Always follow this systematic process before every lift
Identify Crane Model & Confirm Chart Version
Ensure the load chart matches the exact crane model, serial number, and issued counterweight configuration. Charts from different counterweight sets are not interchangeable.
Determine the Lift Configuration
Select the correct chart page based on your setup:
- Outriggers fully extended or on rubber?
- Which counterweight configuration is fitted?
- Are you using a jib (fly) or main boom only?
- Which reeving (parts of line) is configured?
Calculate the Working Radius
Measure (or calculate) the horizontal distance from the crane's slewing centre to the pick point. Round up to the next radius row in the chart — never interpolate between rows.
Use an LMI computer or calculator to confirm actual field radius.
Select the Boom Length Column
Find the boom length you intend to use. If your required boom length falls between two chart columns, you must use the longer boom column (gives lower, more conservative capacity).
Read the Rated Capacity (Gross)
At the intersection of your Radius row and Boom Length column, read the capacity value in tonnes or kg. This is the gross rated capacity.
Calculate Net Lift Capacity
Deduct the weight of all rigging (hook block, slings, shackles, spreader beams) from the gross capacity:
The load you intend to lift (inclusive of packing, attachments) must be ≤ Net Capacity.
Check Utilisation Percentage
Industry best practice limits crane utilisation to ≤ 90% during planning (BS 7121 guidance). This leaves a margin for dynamic effects, wind, and ground settlement.
Interactive Load Chart Simulator
Practise reading a load chart using the controls below
🏗️ Mobile Crane Load Chart Trainer — Zoomlion QY30 (Simplified)
Outriggers fully extended | Main boom | Data for training onlyLive crane geometry. Shows boom angle, length, and radius.
Duty curve — capacity vs. radius. Red dot = your working point.
Load Chart Examples by Crane Type
Simplified worked examples from real crane manuals (training values only)
🟡 Zoomlion QY30 — All-Terrain Mobile Crane
The Zoomlion QY30 is a 30-tonne capacity truck-mounted hydraulic crane widely used across Asia and the Middle East. Its maximum boom length is 43.5 m with a fixed jib.
- Max capacity: 30 t @ 3 m radius
- Main boom range: 11.1 m – 36.0 m (5 sections)
- Jib: 9.5 m / 16 m (optional)
- Counterweight: 6.0 t standard
- Chart delineates: Over-side vs. Over-rear zones
| QY30 — Outriggers Extended | Counterweight: 6.0t | |||||
|---|---|---|---|---|---|
| Radius (m) | 11.1 m | 15.7 m | 20.7 m | 26.0 m | 36.0 m |
| 3 | 30.0 | — | — | — | — |
| 4 | 22.0 | 18.5 | — | — | — |
| 5 | 16.5 | 14.2 | 12.0 | — | — |
| 6 | 13.0 | 11.8 | 10.5 | 8.8 | — |
| 8 | 9.2 | 9.0 | 8.5 | 7.2 | 5.0 |
| 10 | 7.0 | 6.8 | 6.5 | 5.8 | 4.2 |
| 12 | 5.2 | 5.0 | 4.8 | 4.5 | 3.4 |
| 14 | 4.0 | 3.8 | 3.7 | 3.5 | 2.8 |
| 16 | — | 3.0 | 2.9 | 2.7 | 2.2 |
| 20 | — | — | 1.8 | 1.7 | 1.5 |
| 24 | — | — | — | 1.2 | 1.0 |
Values in green = >4t | amber = ≤4t | — = not permitted. Simplified/training values only.
🔵 Terex T340 — Rough Terrain Crane (40T)
The Terex T340 is a 40-tonne rough-terrain crane designed for on–off road use with a single engine driving both travel and crane functions. Common on construction sites.
- Max capacity: 40 t @ 3 m radius
- Main boom: 10.4 m – 36.6 m
- Jib options: 10.7 m, 17.7 m offset
- Counterweight: up to 7.7 t
- Outrigger span: 6.71 m fully extended
| T340 — Outriggers Fully Extended | CW: 7.7t | ||||
|---|---|---|---|---|
| Radius (m) | 10.4 m | 17.7 m | 26.5 m | 36.6 m |
| 3 | 40.0 | — | — | — |
| 4 | 30.7 | 22.0 | — | — |
| 5 | 22.5 | 19.5 | 12.0 | — |
| 6 | 16.8 | 15.4 | 11.2 | — |
| 8 | 11.0 | 10.5 | 9.2 | 6.5 |
| 10 | 8.2 | 7.9 | 7.5 | 5.8 |
| 12 | 6.0 | 5.8 | 5.5 | 4.5 |
| 14 | — | 4.3 | 4.1 | 3.5 |
| 18 | — | 2.7 | 2.5 | 2.2 |
| 22 | — | — | 1.7 | 1.5 |
| 26 | — | — | 1.1 | 0.9 |
Simplified training values only. Always refer to the actual manufacturer's chart.
🟢 Mobile Crane Inspector — Load Chart Inspection Points
Based on the Mobile Crane Inspector Load Charts reference guide, inspectors verify the following when reviewing a crane's load chart compliance:
Chart Currency
Confirm the chart in the cab matches the crane's current configuration — correct counterweight, jib, and attachment fitted.
LMI Programmed Correctly
The Load Moment Indicator must be programmed with the correct crane code that matches the physical setup and chart.
Deductions Applied
Inspector checks that rigging weight (hook block + slings) has been properly deducted from gross chart capacity in the lift plan.
Radius Verification
Inspector verifies the planned radius matches actual site layout. Field radius must be measured — not estimated.
No Interpolation
Capacity values between chart rows or columns must NOT be interpolated. Always round out to the more conservative (lower capacity) value.
Slew Zone Compliance
Inspector flags any operation planned that crosses a restricted slew zone without using the correct (lower) restricted-zone chart column.
🟠 Vehicular & Outrigger Load Tables — Ground Bearing Pressure
The Imperial HD Vehicular Load Tables are used to determine what ground support or cribbing is needed under crane outriggers and carrier axles. They are separate from the crane lift capacity chart but equally critical.
Key Concepts
Outrigger Reaction Force
The vertical force exerted on the ground through each outrigger pad. Calculated from crane weight + counterweight + suspended load + dynamic factors.
Ground Bearing Capacity (GBC)
Maximum safe load the ground can support per unit area (kPa or t/m²). Must be determined before positioning the crane — usually via site investigation or conservative estimates.
Outrigger Pad / Matting
Larger pad area spreads the outrigger force over more ground, reducing pressure per m². Cribbing (timber/steel) is used to further distribute loads to weak ground.
Typical Outrigger Pressure Formula
Ground Pressure must be ≤ Site's Allowable Bearing Capacity.
| Typical Pad Size vs. Allowable Load (example) | ||
|---|---|---|
| Pad Size | Area (m²) | Max Load @ 100 kPa GBC |
| 450×450 mm | 0.20 | 20 kN (~2 t) |
| 600×600 mm | 0.36 | 36 kN (~3.7 t) |
| 900×900 mm | 0.81 | 81 kN (~8.3 t) |
| 1200×1200 mm | 1.44 | 144 kN (~14.7 t) |
| 1500×1500 mm | 2.25 | 225 kN (~22.9 t) |
| Timber mat 3×1.2 m | 3.60 | 360 kN (~36.7 t) |
Key Terms & Glossary
Essential vocabulary for reading and applying load charts
Working Radius
Horizontal distance from crane centreline (slewing axis) to the hook/load centre.
SWL / WLL / Rated Capacity
Safe Working Load = maximum load permitted. WLL (Working Load Limit) is equivalent. Both are derived from the load chart.
Parts of Line (Reeving)
Number of rope segments supporting the hook block. More parts = more capacity but slower speed.
Slew Zone / Slew Sector
Angular range over which a specific chart capacity applies. Capacities differ between over-front, over-side, and over-rear zones.
Counterweight
Ballast fitted to the crane's rear turntable to offset the tipping moment created by the suspended load.
LMI (Load Moment Indicator)
Electronic safety device that monitors actual load vs. rated capacity, triggering alarms/lockouts if limits are approached.
Boom Angle
Angle of the boom above horizontal. Higher angle = smaller radius = greater capacity (up to a limit). Boom angle and radius are inversely related.
Anti-Two-Block (ATB)
Device that stops the hoist when the hook block contacts the boom tip, preventing rope damage and load drop.
Tipping vs. Structural Limit
Chart capacity is governed by whichever is lower — the crane's tipping stability or the structural strength of its components.
The Mission Center — Practical Scenarios
Apply your load chart knowledge to solve real job site challenges
Ready for your first mission?
Select a scenario below to begin your practical assessment.
Knowledge Check — Load Chart Quiz
Test your understanding with 5 scenario-based questions