Lashing calculator: how many top-over straps the load needs
A top-over strap does not hold the load — it presses it down, and friction does the holding. So the surface underneath changes the answer more than the straps do. This works the EN 12195-1:2010 equation and shows you both.
The equation
EN 12195-1:2010 gives the top-over (friction) lashing case. Rearranged to give the number of lashings:
m × g × (cx,y − μ × cz) × fs
n = ─────────────────────────────
2 × μ × FT × sin αThe 2 is there because a top-over lashing presses with both of its legs. FT is the strap's STF, not its LC. The coefficients are fixed by the standard:
| Direction | cx,y | fs |
|---|---|---|
| Forward, braking | 0.8 | 1.25 |
| Sideways, cornering | 0.5 | 1.1 |
| Rearward, accelerating | 0.5 | 1.1 |
cz, the vertical coefficient, is 1.0.
Checked against a published example
The IRU load securing guidelines publish a worked case: two lashings, μ 0.45, STF 400 daN, α 55°, securing 1.4 t forward and 10.9 t sideways. This tool's arithmetic returns 1.37 and 10.93 for the same inputs. That check is why the numbers here are worth reading.
Why the surface matters more than the straps
μ appears twice in the equation. It sets how much restraint the load's own weight already gives you, and it sets how much each strap's downforce is worth. A 2,000 kg load braking forward on 350 daN straps needs eleven lashings on a plastic pallet (μ 0.20) and two on an anti-slip mat (μ 0.60). Nobody puts eleven straps on a pallet, which means loads like that one travel unsecured every day with the paperwork in order.
Where this stops
This is the sliding check for a top-over lashing on a level deck, with the load treated as one rigid block. It does not cover tipping, direct lashing, blocking against the headboard or bulkhead, loads in more than one tier, unstable or loose goods, or the reduced friction you get from oil, ice, dust or a worn deck. For anything you are signing for, work from the standard, and get the training if this is your job.
A tall or narrow load tips before it slides, and tipping is a separate calculation that this tool does not do. Clearing the sliding check does not mean the load is secured.
Where μ already exceeds the required coefficient the equation asks for no straps. That is not an answer you can load on. Vibration walks a load along a deck over hours in a way a static friction figure does not describe, and the load still has to be secured.
Questions people actually ask
Why is LC not used anywhere in this?
Because in a top-over lashing the strap is never loaded to anything like its LC. It supplies pretension — the STF — and that pretension buys friction. LC is the figure for a direct lashing, where the strap itself takes the force. Counting straps against the load's weight using LC overstates what you have by roughly a factor of eight.
It says I need no straps. Is that right?
It means friction alone satisfies the sliding arithmetic in that direction. It does not mean the load is secured. Load securing is required regardless, tipping has not been checked, and a load resting on friction alone will walk along the deck under vibration. Treat a zero as 'friction is doing the work here', not as permission.
What angle should I be aiming for?
As near vertical as the anchor points allow. The equation carries sin α, so a strap at 30° gives half the downforce of one at 90° and you need twice as many. Wide loads with anchor points close to the load are where this quietly goes wrong.
Can I use one strap over several pallets?
Only if they behave as one block, which usually means they are touching and of similar height. A strap over a group presses the outer ones and can leave a shorter one in the middle carrying nothing. This tool assumes one rigid block; if yours is not one, work item by item.
Does the anti-slip mat figure really hold up?
μ 0.60 is the Annex B value for anti-slip material and it is what the standard lets you claim. It assumes the mat is in reasonable condition, sized to the contact area and not sitting on oil or ice. A worn or undersized mat does not give you 0.60, and nothing on the paperwork will say so.
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