BS 7121 is the British Standard for the safe use of cranes. It applies to all types of crane — from mobile cranes and tower cranes to crawler cranes and lorry loaders. It is not optional. If you operate cranes commercially in the UK, BS 7121 is the benchmark that insurers, HSE inspectors and courts will hold you to.
What BS 7121 Requires on Ground and Outriggers
BS 7121 requires that the ground under a crane is assessed before every lift. The Appointed Person must confirm that outrigger pads are large enough to spread the load so pressure stays within the ground's bearing capacity. The standard does not specify a particular pad material. What it requires is that the outrigger load is distributed across enough area that ground pressure stays within safe limits.
Outrigger Load (kN) ÷ Pad Area (m²) ≤ Ground Bearing Capacity (kN/m²)
If the ground bearing capacity is 100 kN/m² and the outrigger is pushing 180 kN through a small steel foot, the maths does not work. You need a pad that spreads that 180 kN across at least 1.8 m². This is the core requirement.
The Appointed Person's Responsibility
The Appointed Person is responsible for planning and supervising the lift. Part of that responsibility is assessing the ground and confirming the pads on the crane are the right size for the job. Not just whatever pads happen to be on the truck.
If the lift plan calls for a pad area of 1.5 m² per outrigger and the operator turns up with 600×600mm pads (0.36 m²), that is a compliance failure before the crane is even rigged. The Pad Size Calculator makes it easy to verify the right size before the crane arrives on site.
Common Compliance Failures
Same Pads for Every Job
A pad that works on concrete may be completely inadequate on soft clay. BS 7121 requires a site-specific assessment, not a one-size-fits-all approach.
Degraded Timber Mats
Pads that have started to split, warp or rot cannot distribute load evenly. The standard requires equipment to be fit for purpose and properly maintained.
Undersized Pads
Undersized pads concentrate the load and can cause the outrigger to punch through soft ground or crack paving. This is exactly what BS 7121 is designed to prevent.
Ground Bearing Values for Compliance
| Ground Type | kN/m² |
|---|---|
| Hard standing (concrete, tarmac) | 400 |
| Compacted hardcore or gravel | 400 |
| Compacted sand or stiff clay | 300 |
| Loose gravel or firm clay | 150 |
| Medium density sand | 100 |
| Soft clay, grass, topsoil | 75 |
| Loose sand, fill, suspect ground | 50 |
| Unknown | 50 (conservative default) |
Note: These values are aligned with IPAF guidance and are the same values used in the CPS Ground Bearing Calculator.
How CPS Pads Support Compliance
UHMW-PE pads distribute load evenly across the full face with no weak spots, no grain direction and no risk of splitting under repeated use. Unlike timber, UHMW-PE does not absorb water, does not rot and does not lose structural integrity over time. A pad that was compliant on day one is still compliant five years later.
Pad Size Calculator
Work out the correct pad size for any outrigger load and ground condition
The calculation is exactly what BS 7121 expects the Appointed Person to have done before the lift starts.
Check Your Pad Selection Before the Lift
The Pad Size Calculator does the BS 7121 calculation for you. Free, no login, works on mobile.
