Estimates capacity at a radius that falls between two published points on a crane's load chart, using straight-line interpolation — the same method most manufacturers specify for reading between chart increments.
Read before use: Only interpolate between two adjacent points from the same load chart, for the same boom length/configuration and the same over-front/over-side/360° condition. Never extrapolate beyond the lowest or highest radius listed on the chart — this tool will refuse to calculate outside the range you enter. Always confirm the final figure against the actual chart in the cab before lifting.
Load chart points (radius vs. rated capacity)
Enter at least two points straight from the chart for the boom length/configuration in use. Add more points to cover a wider range — the tool automatically finds the two points bracketing your target radius.
Target
INTERPOLATED CAPACITY
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Bracketing points—
Actual load—
Utilization—
Quick reference
Why interpolation, not extrapolation
Published chart points already account for both structural strength and tipping stability limits at that specific radius — the relationship between radius and capacity isn't a simple formula across the whole chart
Between two adjacent listed points, straight-line interpolation is accepted practice and is what most manufacturers explicitly permit
Beyond the lowest or highest listed radius, there's no safe way to estimate capacity — the chart simply doesn't cover that condition
Match the exact configuration
Boom length, counterweight, outrigger spread, and over-front/over-side/360° rating all change the chart you should be reading
Don't mix points from two different configurations, even if they're on the same chart page
Re-check if the boom angle or length changes during the lift — capacity applies to the configuration at the moment of lift, not the start
Include the full load
Hook block, headache ball, slings, shackles, and any spreader or lifting beam all count toward the load on the chart
The chart's rated capacity is a hard limit — it's not a target to plan close to
Good practice
Always verify the interpolated figure against the physical chart in the crane cab before lifting
A lift plan should already specify the intended radius and load — use this tool to sanity-check, not as the primary planning method
If the target radius is very close to a listed point, just read that point directly rather than interpolating