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Technical GuideHow to Measure a Crane
The crane measurements needed for a quote: how to measure span, lifting height, hook approach distance, runway length and headroom.
Span
Span is the centre-to-centre distance between the two runway rails the crane travels on. The most common mistake is giving the distance between walls or columns as the span; because the runway usually sits on brackets, these two measurements differ.
Take the span measurement at several points along the runway. Older buildings can have columns out of true; if the span isn't constant along the runway, that's something that needs to be known before manufacturing, not after.
Lifting height
Lifting height is the total vertical travel the hook can make: from its lowest position (usually the floor or a pit bottom) to its highest.
When working this out, include the longest part you'll be lifting and the length of the sling or lifting beam used. If a part needs to clear 6 metres and you use a 2-metre sling, the required lifting height is 8 metres, not 6.
Hook approach distance
Hook approach is the closest the hook can get to the runway centreline. Because the trolley and hoist have a certain width, the hook can never reach all the way to the rail — a dead zone remains at each end.
That dead zone directly shrinks the crane's usable area. If the hook can't reach a bench against the wall, the crane doesn't do the job even if it looks like it covers the whole facility on paper. Projects needing a short approach distance choose the trolley type accordingly.
Headroom and obstructions
The crane's bridge has to clear the lowest obstruction in the facility. While measuring, note: the underside of the roof truss, light fittings, ventilation ducts, the sprinkler line, pipe and cable trays, and beams above doorways.
These obstructions often limit lifting height independently of the building's height, and directly affect the single-girder vs. double-girder decision.
The order to follow when measuring
- Establish the capacityDetermine the heaviest load that will hang on the hook, including sling and lifting-beam weight.
- Measure the spanMeasure between the two runway rail centrelines, at several points along the line.
- Establish the lifting heightWork out the vertical travel between the hook's lowest and highest positions, adding the length of the part and the sling.
- Measure the runway lengthNote the total distance the crane can travel.
- Note the obstructionsRecord the underside levels of the roof truss, lighting, ventilation and pipework.
- Write down the duty cycleLifts per day, average load and number of shifts — duty class comes from these.
| Measurement | What it means | How to take it |
|---|---|---|
| Span | Distance between the two runway rail centrelines | Along the rail, at several points, centre to centre |
| Lifting height | The hook's total vertical travel | From lowest to highest position |
| Runway length | The total distance the crane can travel | From one end of the rail to the other |
| Hook approach | The hook's closest distance to the rail | Given by the manufacturer, depends on trolley type |
| Headroom | Gap between the rail top and the lowest obstruction | From rail level to the obstruction's underside |
| Capacity | The heaviest load on the hook | Including sling and lifting beam weight |
With these six figures in hand, you have enough to request a quote.
Technical terms
| Term | What it means |
|---|---|
| Span | The distance between the centrelines of the two runway rails the crane travels on. |
| Hook approach | The smallest distance the hook can approach the runway centreline. |
| Headroom | The gap between the top of the rail and the lowest obstruction on site. |
| Lifting beam | A beam attached to the hook to hold a long or unbalanced load at two points. |
| Sling | The rope, chain or webbing element that attaches the load to the hook. |
Frequently asked questions
Should I take the measurements myself?
Your own measurements are enough for a preliminary quote. Before ordering, exact measurements need to be taken on the runway and the building — this is standard practice for the manufacturer to carry out.
What if there's no runway yet?
Then it's engineered together with the crane. In that case the building's column spacing, bracket levels and load capacity are measured, and the runway is designed accordingly.
Is it OK to give an approximate span?
For a preliminary price, yes. But manufacturing never proceeds on an approximate measurement: a difference of a few centimetres means a crane that doesn't sit on the rail at installation.