Crane Lift Plan Gross Mass Estimator
Work out the gross lift mass a crane must handle before you open the load chart. This tool sums the load with every item below the hook — slings, shackles, spreader beams, the hook block and any headache ball — then adds a contingency allowance, so the figure you check against rated capacity is the real one, not just the bare load weight.
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the load mass in kilograms — ideally from the drawing, data plate or a load cell, not a guess.
- Add the mass of the rigging gear (slings, shackles, spreader), the hook block, any headache ball/auxiliary and anything else hanging below the hook; leave a field blank if it does not apply.
- Set a contingency allowance (default 10%) to cover estimating error, trapped water/mud, ice or unweighed attachments, then read the gross lift mass in kg and tonnes to compare with the crane's rated capacity at the working radius.
How it works
Total below-the-hook gear is the sum of the rigging, hook block, headache ball and any other gear you enter. The load plus that gear gives a subtotal, and the gross lift mass = subtotal × (1 + contingency/100). The contingency amount shown is simply subtotal × contingency%. The gross lift mass is what must sit within the crane's rated capacity at the actual radius and configuration read from the load chart — the chart already deducts the crane's own block, rope and jib mass, so you count only the load and the rigging you add.
Worked example
Worked example. An 8,000 kg vessel is rigged with 300 kg of slings and shackles and lifted on a 200 kg hook block, with a 10% contingency. Below-the-hook gear = 300 + 200 = 500 kg; subtotal = 8,500 kg; contingency = 850 kg; gross lift mass = 8,500 × 1.10 = 9,350 kg = 9.35 t. You then check 9.35 t against the crane's rated capacity at the planned radius.
Common mistakes
- Checking only the bare load against the chart and forgetting the slings, shackles, spreader and hook block — the gear can be a large share of the gross on a light load.
- Double-counting the crane's own hook block or jib: the load chart's rated capacity already deducts them, so only add rigging you supply below the chart's stated deductions.
- Using a nominal or 'about' weight instead of a confirmed weight — always verify from drawings, the data plate or a load cell, and keep a contingency for the unknowns.
Frequently asked questions
Why add a contingency if I already know the weights?
Even confirmed weights carry uncertainty — trapped water or mud, ice, paint, weld and fit-up additions, or attachments not weighed. A contingency (commonly 5–25% depending on how well the weight is known) keeps a margin so a small underestimate does not push you over the chart. Set it to zero only if the gross is a verified, all-inclusive figure.
Is the gross lift mass the same as what I read on the load chart?
No. The gross lift mass is what you must LIFT. The load chart gives the rated capacity available at a given radius and configuration, after the crane's own hook block, rope and jib mass are deducted. You compare the two: the gross lift mass must be less than the rated capacity, with the margin your procedure requires. A licensed crane crew and rigger plan the actual lift to AS 1418 / AS 2550.
Related tools
- Crane Lift Utilisation Calculator
- Sling Angle Load Factor Calculator
- Sling Length for Angle Calculator
- Wire Rope SWL / Load Checker
- Tagline Wind Force Calculator
- Block & Tackle Mechanical Advantage Calculator
Explore more in Rope, Rigging & Lifting.
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.