Nine out of ten ramp orders that come back to us for modification fail on the same detail: the height. Not the capacity, not the deck width — the height, measured once, on one trailer, on a day when that trailer happened to be empty and its air bags were where they should be. The survey below takes two hours and costs nothing. It is the difference between a ramp that works on every trailer in your yard and one that works on the trailer you measured.
Why the Number on the Trailer Isn’t Your Ramp Height
Trailer paperwork tells you interior height and cubic capacity. It does not tell you how far the floor sits above the ground on the day you unload, because that number is not fixed. It moves with suspension setting, load, tyre size and wear, fifth-wheel height on the tractor, and whether the driver dumped the air before backing in.
Take a 53 ft air-ride dry van as an example. OEM spec sheets for that trailer list a coupler height of 1,194 mm (47 in) and a dock height of 1,270 mm (50 in) — measured empty, at ride height, on a level floor. Load 20 tonnes into it and the rear sill drops. Dump the air bags and it drops further. On the European side the spread is wider still: the standard dock is 1,000–1,200 mm, and the Irish HSA’s goods-reception guidance puts trailer platform heights at 1.00–1.35 m, with container-carrying chassis running up to about 1,450 mm. A fleet that mixes curtain-siders, containers and vans can span 700 mm of floor height. That spread is the entire reason a survey exists.
| Vehicle type | Typical floor height at rest | What moves it |
|---|---|---|
| 53 ft dry van, air-ride (US), at ride height | 1,270 mm / 50 in | Load, air-bag pressure, dump valve |
| EU curtain-sider / tautliner | 1,000–1,350 mm / 39–53 in | Axle configuration, load, tyre size |
| Container on a skeletal chassis | up to 1,450 mm / 57 in | Chassis deck height, twistlock setting |
| Flatbed | about 1,220 mm / 48 in | Deck thickness, suspension, load |
| Panel van / Sprinter | 500–700 mm / 20–28 in | Model, load, rear step |
Treat that table as a starting point for a conversation, never as a design value. The only numbers that belong in a purchase order are the ones you measured on your own trailers, on your own apron.
The Survey Kit and a Two-Hour Procedure
You need five things: a laser distance meter, a 2 m spirit level or a string line with a line level, a 5 m tape, chalk, and a phone. The laser is for the vertical drops; the level is there because ground is rarely flat and a tape held by eye will lie to you by 20 mm over 3 m.
- Pick three trailers, not one. Take the one with the lowest sill and the one with the highest, plus a typical unit. If all three measure within 50 mm, one ramp will serve the fleet.
- Measure at the rear threshold, on the centreline. That is where the lip lands. Measuring mid-deck tells you about the floor, not about the interface.
- Measure twice: bags at ride height, then dumped. Write both numbers down. The ramp has to work at the higher of the two and still be usable at the lower.
- Measure the dock edge and the apron separately. The rise your ramp has to climb is the difference between the two, not the dock height on the drawing.
- Photograph the tape against the reference point and label the photo with the trailer plate. When a drawing is queried three weeks later, the photo settles it.
One trap catches almost everyone: measuring to the top of the rear bumper or the ICC bar instead of the floor. The lip has to rest on the trailer floor, and on most vans the bumper sits 100–150 mm below it. Measure the floor, mark the floor with chalk, and photograph the mark.
The Twelve Fields on the Sheet
Print this as a table and fill one column per trailer. A supplier can quote from it without a single follow-up email, which is worth about a week of your project schedule.
| # | Field | How to measure |
|---|---|---|
| 1 | Trailer ID / plate | Photograph the plate |
| 2 | Floor height, bags at ride height | Laser from floor to apron, at rear threshold centreline |
| 3 | Floor height, bags dumped | Repeat with suspension dumped |
| 4 | Interior height at the door | Tape, floor to header |
| 5 | Door opening width and height | Tape at the narrowest point, including door tracks |
| 6 | Dock edge height above apron | Laser or level and tape, at the loading position |
| 7 | Apron grade over the first 5 m | Level or string line; rise ÷ run × 100 |
| 8 | Ground surface and bearing | Concrete, asphalt or gravel; note cracks and drains |
| 9 | Clear approach distance | Tape from dock face to first obstruction |
| 10 | Forklift model, unladen weight, tyres | From the data plate; note solid or pneumatic |
| 11 | Heaviest load handled | Pallet weight, not average |
| 12 | Environment | Indoor, outdoor, washdown, ice, salt |
Turning Heights into Ramp Length
Once you have the rise, the grade decides the length, and the grade is set by what will drive up the ramp — not by preference. EN 1398 governs dock levellers rather than portable ramps, but its slope-by-equipment table remains the most useful published reference for anyone sizing a ramp:
- Manually operated wheeled container or pallet truck: 3%
- Powered pallet truck: 7%
- Electric forklift: 10%
- IC (diesel/LPG) forklift: 12.5% — 7.1°
Length is then simple arithmetic: L = H ÷ G, where H is the rise and G the grade as a decimal. A 1,270 mm rise at 10% needs 12,700 mm of slope before you add the level platform at the top.
| Rise (mm) | at 8% | at 10% | at 12.5% |
|---|---|---|---|
| 1,000 mm / 39.4 in | 12,500 mm | 10,000 mm | 8,000 mm |
| 1,200 mm / 47.2 in | 15,000 mm | 12,000 mm | 9,600 mm |
| 1,300 mm / 51.2 in | 16,250 mm | 13,000 mm | 10,400 mm |
| 1,450 mm / 57.1 in | 18,125 mm | 14,500 mm | 11,600 mm |
Two corrections turn slope length into an actual machine. Add the level platform at the top — 2,200–2,600 mm on our hydraulic ramps — and add the lip, which must reach past the trailer sill by at least 100 mm. That is why a 10-ton ramp for a 1,200 mm dock ends up at roughly 10.2–10.5 m overall: about 7.6 m of slope plus a 2.6 m platform. It also explains the compromise most yards make. A 1,200 mm rise at 10% wants 12 m of slope, and a 12 m ramp rarely fits a busy apron; at 12.5% you are down to 9.6 m, which is where most mixed fleets land. Push a 1.2 m rise into 8 m of slope and you are at 15% — outside any published forklift guideline, and outside where we would put a loaded counterbalance truck.
There is also a legal floor under all of this. OSHA 29 CFR 1910.178(n)(7)(i) requires a loaded forklift to travel with the load uphill on any grade steeper than 10% — which on a ramp means reversing down and driving up, and which is a training and route-planning issue as much as a ramp issue. If your operators will not accept that, size the ramp at 8–10% and find the extra length in the yard. If the yard is tight and the trucks are 5 t and up, the heavy-duty hydraulic yard ramp carries the capacity at the same working height.
Four Things a Tape Measure Won’t Tell You
1. Whether the ground will take the point load
A 4.5 t forklift carrying 1.5 t puts roughly 65% of that 6 t on the front axle. Split across two wheels, each carries about 1.95 t — a 19 kN point load on a contact patch of perhaps 300 × 200 mm. That is the number to take to whoever owns the slab or the asphalt, not the gross weight. A ramp foot sitting on 100 mm of un-reinforced asphalt beside a drain will punch through in the first wet season.
2. Where the water goes
Dock aprons are usually graded away from the building at up to about 4%. If yours falls towards the door, the ramp foot sits in a puddle, the deck stays wet, and the first frost turns it into a slide. Measure the apron grade in both directions and note the drain positions.
3. Whether the ramp fits the openings
A 2,200 mm deck through a 2,340 mm container door leaves 70 mm per side. That is fine for a careful operator and unacceptable for a busy yard. Check the narrowest opening the ramp will ever pass through, including door tracks and any shelter curtain.
4. How much room you actually have
Ramp length plus approach plus turning circle. A 10.5 m ramp with a 2.6 m platform needs about 13 m of clear apron in front of the dock before a tractor unit can swing. If you have 9 m, you are choosing between a shorter, steeper ramp and a folding one — a decision that belongs in the survey, not in the workshop.
What to Send Your Supplier
One page is enough: a hand sketch showing the six critical dimensions, the twelve-field sheet filled in for three trailers, three photographs (rear threshold, dock edge, apron), the load case, and the destination port. With that, a quotation should come back with a drawing rather than a question — and the drawing is what protects you, because it is the only document that proves what you ordered. If your fleet includes container work at ground level, look at the container ramp as well; if the heights vary widely, a hydraulic yard ramp with a 1,200–1,680 mm working range will absorb the spread that a fixed ramp cannot.
Frequently Asked Questions
Should I measure the trailer loaded or empty?
Both, and record both. Size the ramp for the highest floor you will ever serve, because a ramp can always be set down lower but can never be made taller. The loaded, bags-dumped figure matters for whether the lip still lands on the sill rather than dropping into the gap.
How accurate does the measurement need to be?
Within 10 mm at the trailer floor and the dock edge; within about 50 mm on apron grades. The lip overlap is the tight tolerance in the system — under 100 mm of engagement and you are relying on the driver’s judgment instead of the geometry.
Can one ramp serve a mixed fleet?
Yes, if the spread between the highest and lowest floor is under about 150 mm. Beyond that, either accept that the ramp lives at one dock and the fleet adapts, or buy hydraulic adjustment and cover the range properly.
Do I measure the dock height or the ground?
The difference between them. A “1,200 mm dock” measured to a worn apron 60 mm lower than the drawing is a 1,260 mm climb, and that 60 mm is exactly the kind of error that turns a working ramp into a return shipment.
Get Your Numbers Checked
Send us the filled sheet and the three photographs before you order anything — even if you are buying elsewhere. We will tell you what rise and grade your numbers imply, whether the ramp you are considering will actually reach the sill, and what we would build for that yard. Contact our engineering team, or browse the mobile yard ramp range to see the lengths and working ranges the arithmetic above maps onto.
