What 30 tonne-metre actually means
Crane ratings confuse almost everybody, and the confusion costs people money. Here is the arithmetic, and why the load chart is the only answer that counts.
13 September 2026 · 6 min read
Guide
Lorry loader cranes are rated in tonne-metres, written tm or TM. Ours is a 30 tonne-metre HMF. The single most common misunderstanding in this trade is that this means it lifts 30 tonnes. It does not, and it never did.
The arithmetic
A tonne-metre rating is load multiplied by radius. The radius is measured from the centre of the crane column, not from the back of the lorry.
So a 30 tonne-metre crane could in theory lift 30 tonnes at one metre from the column. Nobody lifts anything at one metre, so that figure is a specification, not a capability.
The useful version is the other way round: divide the rating by the distance you need to reach.
| Radius from the column | Theoretical capacity, 30tm |
|---|---|
| 5 metres | about 6,000 kg |
| 10 metres | about 3,000 kg |
| 15 metres | about 2,000 kg |
| 20 metres | about 1,500 kg |
Why the real figure is always lower
Those numbers are the theory and the real capacity is below them, for reasons that apply to every loader crane on the road.
The crane has to lift its own boom before it lifts anything of yours, and each extension section adds weight at the worst possible place. There is a safety margin built into every machine. Stability depends on the outriggers, the ground under them and the position of the load relative to the vehicle, so the same crane can be rated differently to the side than to the rear.
This is why every crane carries a load chart, and why that chart, not the headline rating, is the only figure that decides whether your lift is on.
What to tell a haulier when you ring
Those four answers settle almost every job in a two-minute phone call. A photograph taken from where you think the lorry would park answers most of them at once.
- What the item weighs, as accurately as you can
- How far it has to go from where the lorry can realistically stand
- Whether anything is in the way: a wall, a hedge, a conservatory, overhead cables
- What the ground is like where the outriggers will sit
Our own machine, honestly stated
Ours is a 30TM HMF crane with roughly 10 metres of working reach, on a cheesewedge body with a 10 ton load capacity. At full reach that is in the region of three tonnes before deductions, and rather more as the load comes closer in.
If your job is near the edge of that, we will say so. Turning up and failing helps nobody.
Questions
Common questions
- Does a 30 tonne-metre crane lift 30 tonnes?
- No. Tonne-metre is load multiplied by radius, so 30tm is 30 tonnes at one metre from the column, which is not a real lift. At 10 metres the theoretical figure is around 3 tonnes, and the actual figure is lower once boom weight and the safety margin are taken off.
- Where is the radius measured from?
- From the centre of the crane column on the lorry, not from the edge of the vehicle or from where you are standing. People routinely underestimate it by a few metres, which matters a lot at the limit.
- Why does the ground matter?
- Because the outriggers transfer the whole weight of the lorry and the load into a small area. Soft ground, a drain cover, a recently dug trench or an unsupported edge can all turn a routine lift into a dangerous one.
What we do
Hiab hire and haulage across Cornwall and Devon
30TM crane, 10 metres of reach, 10 ton capacity, based near Truro. Tell us the weight, the distance from the lorry and what is in the way, and you will get a straight answer.
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