What Size Crane Do I Need? Load, Radius and Height Explained

"What size crane do I need?" is the first question on almost every lift we quote, and the honest answer is that the weight of the load is only one third of it. A crane's tonnage is the most it can lift in its best position: boom fully retracted, load close in, outriggers fully out. Move the load a few metres further away and that number falls quickly. This guide explains the three numbers that decide crane size, so you can describe a lift in a way that gets the right machine first time.

Why a 25 Ton Crane Rarely Lifts 25 Tons

Every mobile crane is named after its maximum rated capacity, which applies at the shortest radius the crane can work at, a few metres from its centre of rotation. Real lifts almost never happen there. The crane has to stand clear of the building, the trench or the truck, and the load has to travel to where it is needed. Further out, a crane may be able to lift only a small fraction of the figure on its side. That is why a light rooftop unit lifted far from the crane can need a bigger crane than a much heavier generator set down right beside it.

The Three Numbers That Size a Crane

1. The Total Lifted Weight

Start with the load's weight from the manufacturer's data plate, the delivery note or the drawings, not an estimate. Then add everything else hanging from the hook: the hook block, slings, shackles, spreader beams and any lifting frame. Rigging on a heavy lift can add several hundred kilograms. The crane's capacity has to cover the total, not just the item.

2. The Radius

Radius is the horizontal distance from the crane's centre of rotation to the centre of the load, measured where the load is picked up and where it is set down. Use the larger of the two. On a tight site, the crane's own set-up position decides the radius: if the crane can only stand on the road outside a plot, the radius is the distance from that road to the far side of the roof, not to the near edge.

3. The Height and Obstructions

The boom has to be long enough to lift the load over the highest point in its path, such as a parapet, a roof edge, a pipe rack or a neighbouring building, with clearance for the rigging below the hook. More height means more boom, and more boom means less capacity at the same radius. Note anything the boom must clear on the way, including overhead power lines.

Typical Jobs for Each Crane Class

Each class has its own page with worked examples: 25 ton crane rental, 50 ton crane rental, 100 ton crane rental, 200 ton crane rental and 500 ton crane rental.

A Worked Example

A contractor needs to lift a 3.5 ton rooftop unit onto a two-storey building. The rigging and hook block add about 0.5 ton, so the crane must carry 4 ton in total. The crane can only stand on the service road, which puts the set-down point 18 metres away, and the boom must clear a 9 metre parapet. The check is the chart value at 18 metres, read on the next larger radius row, with enough boom to clear the parapet. If a smaller crane's chart shows less than 4 ton there, a larger class is needed, even though the unit itself is light. If the crane could stand inside the plot at 8 metres, the smaller crane might be enough, which shows how much the set-up position matters.

Our guide on how to read a crane load chart walks through this check step by step.

Do Not Forget the Set-Up Space

• ✓Outrigger footprint: larger cranes need a wider, firmer pad than many sites expect
• ✓Counterweight: 100 ton and larger cranes often arrive with counterweight on separate trucks, which need room to unload
• ✓Access: gate widths, turning circles, ramps and overhead height on the way in
• ✓Ground: backfill, trenches, buried services and soft sand under the outrigger positions
• ✓Tail swing: the counterweight swings behind the crane and needs a clear zone

What to Send for a Crane Recommendation

• ✓Load weight and dimensions, with photos or a data sheet
• ✓Pick-up and set-down positions, ideally marked on a site plan or a screenshot from a map
• ✓Lift height and the highest obstruction in the path
• ✓Where the crane can stand, and what the ground is (asphalt, interlock, compacted sand, open desert)
• ✓The site location and preferred date

With those details we confirm the figure from the exact crane's load chart before we quote, and survey the site first for heavy lifts. For lifts anywhere in the country, see mobile crane rental across the UAE or send the details on WhatsApp.