Crane Load Chart Calculator
Crane capacity at radius from boom length and load.
About this calculator
Real crane load charts are dense, non-linear tables that vary by boom configuration, counterweight, and outrigger spread — this calculator instead uses a deliberately simplified linear model so you can get a fast sanity check on whether a lift is even in the right ballpark before consulting the manufacturer's actual chart. It treats capacity as falling off roughly linearly from your entered maximum rated capacity (at minimum radius) down toward a floor of 10% of that maximum as the working radius approaches the boom length. Total suspended load combines your load weight and rigging weight (block, hook, slings), and utilization is that total expressed as a percentage of the capacity at your radius.
The calculator also reports a safe working load set at 85% of rated capacity — a common conservative working limit used on many job sites, distinct from and below the absolute rated maximum — and flags the lift as overloaded outright if total load exceeds the rated capacity at that radius. Net capacity backs out the rigging weight to show what's left for the actual payload. Because the underlying capacity curve is a simplification rather than manufacturer chart data, treat any result near the safe-working-load or rated-capacity threshold as a signal to pull the real load chart for your specific crane, boom length, and configuration — never plan an actual lift off this estimate alone.
Inputs
Results
Capacity at radius (lb)
27,500
How to Use This Calculator
- Enter the crane's maximum rated capacity (lb) from the load chart at minimum radius.
- Set the current boom length (ft) for the configuration you are using.
- Enter the working radius (ft) — the horizontal distance from the crane's center of rotation to the load.
- Input the load weight (lb) and rigging weight (lb) to calculate total suspended load.
- Check Capacity at radius (lb) and Utilization (%) to confirm the lift is within the safe working load; a result of 1 in Overloaded means the lift must not proceed.
How the result changes with Max capacity (lb)
| Max capacity (lb) | Capacity at radius (lb) |
|---|---|
| 25,000 | 13,750 |
| 37,500 | 20,625 |
| 75,000 | 41,250 |
| 125,000 | 68,750 |
What each input means
- Max capacity (lb)
- Crane maximum rated capacity at minimum radius.
- Boom length (ft)
- Current boom length in feet.
- Working radius (ft)
- Horizontal distance from center of rotation to load.
- Load weight (lb)
- Weight of the load being lifted.
- Rigging weight (lb)
- Weight of rigging, block, and hook.
What each result means
- Capacity at radius (lb)
- Rated capacity at the working radius.
- Utilization (%)
- Total load as percentage of rated capacity.
- Safe working load (lb)
- 85% of rated capacity (common working limit).
- Net capacity (lb)
- Available capacity after rigging deduction.
- Overloaded (0/1)
- 1 = load exceeds rated capacity.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersMax capacity (lb) = 50000, Boom length (ft) = 100, Working radius (ft) = 50, Load weight (lb) = 10000 = 5 input(s) provided
- Calculate Capacity at radiusCapacity at radius = round(capacityAtRadius)27500 = 27500
- Calculate UtilizationUtilization = round((totalLoad / roundedCapacity) * 10000) / 10038.18 = 38.18
- Calculate Safe working loadSafe working load = round(roundedCapacity * 0.85)23375 = 23375
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does capacity never drop all the way to zero as the working radius increases?
The formula is maxCapacityLb times the greater of 0.1 or (1 minus the radius-to-boom-length ratio times 0.9), which puts a hard floor at 10% of maximum rated capacity even once radius equals or exceeds boom length. Real cranes do retain some residual lifting capacity at long radius rather than dropping to zero, so the floor keeps the simplified model from producing an unrealistic result at the chart's extreme end.
What's the difference between 'safe working load' and 'rated capacity at radius' in the results?
Rated capacity at radius is the calculator's estimate of the crane's maximum capacity at your specific working radius, while safe working load is a more conservative figure set at exactly 85% of that number. The overloaded flag only trips when total load exceeds the full rated capacity, but exceeding the safe working load first is meant as an earlier warning, since many job sites treat that 85% line as the actual working limit rather than the rated maximum.
Why does adding rigging weight lower net capacity but not change the utilization percentage calculation method?
Rigging weight is added to load weight to form total suspended load, which is what drives the utilization percentage (total load divided by capacity at radius) — so rigging weight does affect utilization, just indirectly through that sum. Net capacity is a separate, simpler output: it's rated capacity at radius minus rigging weight alone, showing how much payload capacity remains once the hook, block, and slings are accounted for.
Does changing the boom length by itself change the crane's capacity?
Yes, indirectly: boom length only enters the formula through the radiusRatio (working radius divided by boom length), so a longer boom at the same working radius produces a smaller ratio and therefore a slower capacity falloff. This mirrors real crane behavior where a longer boom extended to the same radius typically retains more capacity than a shorter boom stretched to its limit at that same radius.
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