Freight Reference · Equipment
Semi-Truck Trailer Types, Dimensions & Capacity
What every full-truckload trailer is, how big it is inside, how much it carries, and which one your freight needs. Then heavy haul in depth: goosenecks, axle limits, the bridge formula and superloads, with models drawn to scale.
Drawn to scale from typical dimensions. The green block is the tallest freight an RGN carries under 13'6" (most states): 11'10" above a 20 in well.
At a glance
Every trailer, side by side
The fast reference: usable height, weight capacity, and the freight each trailer is built for. Tap a name to jump to its full spec sheet.
| Trailer | Usable height | Cargo payload | Best for |
|---|---|---|---|
| Dry Van | 9′2" (110") | 42,000–45,000 lb | Standard enclosed, palletized & boxed freight |
| Refrigerated (Reefer) | 8′8" (104") | ~43,000 lb | Temperature-controlled (refrigerated or frozen) |
| Flatbed | open — up to ~8′6" (102") | 46,000–48,000 lb | Open-deck, oversized, side/top-loaded freight |
| Step Deck | open — up to ~10′ (120") | 44,000–47,000 lb | Tall open-deck freight (~8′6" to 10′) |
| Double Drop | well — up to ~11′6"–12′ (138–144") | ~40,000 lb | Over-dimensional / very tall freight (10–12′) |
| RGN (Removable Gooseneck) | well — up to ~12′ (144") | 40,000–44,000 lb | Drive-on heavy equipment (excavators, dozers) |
| Conestoga | up to ~8′6" (102") | 42,000–44,000 lb | Open-deck freight that needs weather protection |
| Straight / Box Truck | up to ~9′ (108") | ~10,000 lb (26′ non-CDL) | Urban / limited-access, smaller loads |
| Power Only | n/a — you supply the trailer | — | Tractor only; customer provides the trailer |
Federal limits: 80,000 lb gross · 8′6″ (102″) wide. Height is state-set: 13′6″ in most of the East and Midwest, 14′ across much of the West and the Plains (Arizona stays at 13′6″), 14′6″ in Colorado and Nebraska, 15′ in Alaska. Payloads shown are legal usable weight under the 80,000 lb cap, not trailer GVWR; actual payload depends on tractor weight. Sizing a partial or full load? Truckload Calculator · Linear Feet Calculator.
Find your trailer
Which trailer fits my freight?
Enter your tallest item and total weight, flag refrigeration or open-deck loading, and we'll point you to the right trailer — using the same logic our quote wizard runs.
Matched on usable height, weight, refrigeration, and loading method — the same logic our quote wizard runs.
Open-deck clearance
Why a lower deck fits a taller load
On an open deck, how tall your freight can be is simply the legal height limit minus the deck height. A lower deck buys more usable height under the same ceiling — which is exactly why step decks and double drops exist.
Drawn to scale: each open deck can load right up to the same legal ceiling, so the deck is the only thing that changes. As the deck (gray) drops left → right, the usable cargo height (green) grows — which is exactly why a step deck or double drop hauls what a flatbed can't. Enclosed dry vans and reefers are fixed-height boxes; their dimensions are in the table above.
*13′6″ is the height limit in most of the East and Midwest; much of the West and the Plains allow 14′ (Arizona stays at 13′6″), Colorado and Nebraska 14′6″, and Alaska 15′.
To scale
Check your load against a state's height
Pick an open deck and a state, then size your load. The verdict comes from the same check our team uses. Decks are ranges (a step deck runs 36 to 42 in), so a load near the line can depend on the trailer; the model draws the highest deck.
Depends on the trailer
- Height: legal only on a deck 40 in or lower (they run 36 to 42 in). On a 42 in deck it is 13'8" overall, over the limit in common (13'6"). Ask the carrier for the loaded deck height.
Not checked here: axle weights and the bridge formula, overall length, and route rules like escorts and travel times.
Check every state on the route.
Legal limits only. A load over any of them needs permits from every state on the route where it is over.
Watch
Trailer types explained, in 11 minutes
Every trailer in the spec sheets below, what fits on it, and how to pick, with the trailer finder at work.
Trailer types explained (11:05). Chapters and transcript · More freight videos
Spec sheets
Enclosed: dry van & reefer
Fully boxed equipment that protects freight from weather and loads at a dock. The default for general and temperature-controlled freight.
Dry Van
The default for general freight — a fully enclosed box that protects almost anything that fits inside and doesn't need temperature control.
| Inside length | 52′6" (53′ trailer) |
|---|---|
| Inside width | 8′3" (99") |
| Inside height | 9′2" (110") |
| Door opening | ~98" × 110" swing, ~93" × 104" roll-up (W×H) |
| Cargo payload | 42,000–45,000 lb |
| Pallet positions | 26–30 (48×40) |
| Cubic capacity | ~3,400–3,800 ft³ |
A roll-up (overhead) door typically takes ~4" of width and ~6" of height off the opening versus swing doors — worth checking if your load is wide or tall.
Refrigerated (Reefer)
A dry van with an insulated body and a front-mounted cooling unit — for anything that has to stay cold, frozen, or within a set temperature band.
| Inside length | 51′7" |
|---|---|
| Inside width | 8′1¼" (97¼") |
| Inside height | 8′7"–8′8" (104") |
| Temp range | ‒20°F to 70°F |
| Cargo payload | ~43,000 lb |
| Cubic capacity | ~3,000–3,400 ft³ |
The reefer unit and insulation steal 2–5 ft of length in the nose and a couple inches all around — usable space is a bit smaller than a dry van, which is why payloads run lighter.
Spec sheets
Open deck: flatbed & step deck
No walls or roof — load from any side or the top by crane or forklift. For freight that's oversized, very tall, or won't fit through a van's doors.
Flatbed
An open deck with no walls or roof — load from any side or the top by crane or forklift. The workhorse for building materials, machinery, and anything that won't fit in a van.
| Deck length | 48–53′ |
|---|---|
| Deck width | 8′6" (102") |
| Deck height | ~5′ (60") |
| Max freight height | ~8′6" (102") legal |
| Cargo payload | 46,000–48,000 lb |
There's no roof, so legal height is the only ceiling: ~8′6" of cargo on top of a 5′ deck reaches the 13′6" road limit. Open freight must be tarped and strapped/chained.
Step Deck
A flatbed with a lower main deck (and a short upper deck near the nose). The drop lets you haul taller freight than a flatbed without a permit.
| Lower deck length | 37–42′ |
|---|---|
| Upper deck length | 10–11′ |
| Deck width | 8′6" (102") |
| Lower deck height | 36–42" |
| Max freight height | ~10′ (120") legal |
| Cargo payload | 44,000–47,000 lb |
Also called a "drop deck." The lower deck sits about 18" below a flatbed, so freight up to ~10′ tall still clears the 13′6" limit. Heavy equipment can be forklifted or ramped on.
Spec sheets
Heavy-haul & over-dimensional
Lowered decks that keep tall, heavy machinery under the 13'6" road limit. When a flatbed or step deck isn't low enough, these are next. Lowboy is the heavy-haul name for the double drop shape, and an RGN is a lowboy whose gooseneck comes off.
Heavy-haul loads are often over-dimensional — taller, wider, or heavier than the legal limits. Expect state permits, routing, and sometimes escorts. See state DOT limits.
Double Drop
A deck that drops to a low well in the middle, between a raised front deck and the rear axles — for the tallest freight that still moves on standard equipment.
| Well length | 24–30′ |
|---|---|
| Deck width | 8′6" (102") |
| Well floor height | 18–24" |
| Max freight height | ~11′6″–12′ in the well |
| Cargo payload | ~40,000 lb (up to 44,000) |
The center well sits low to the ground, so tall freight rides under the legal ceiling. Freight is loaded into the well by crane or forklift; very tall/wide loads may still need a permit.
RGN (Removable Gooseneck)
A double drop whose front gooseneck detaches and lowers the deck to the ground as a ramp — so heavy machinery can drive or roll straight on.
| Well length | 26–30′ |
|---|---|
| Deck width | 8′6" (102") |
| Well floor height | 18–24" |
| Max freight height | ~12′ (144") in the well |
| Cargo payload | 40,000–44,000 lb (more with added axles) |
The detachable front lets the deck drop to ground level so equipment drives on under its own power. With extra axles (flip/jeep), RGNs carry far heavier loads, but those move under permit.
Spec sheets
Specialty & flexible equipment
Purpose-built options for weather-protected open freight, tight urban deliveries, and moves where you bring your own trailer.
Conestoga
A flatbed or step deck fitted with a retractable rolling tarp on a frame — open-deck loading with the weather protection of a van.
| Length | 48–53′ |
|---|---|
| Width | 8′6" (102") |
| Usable height | 96–102″ (up to ~110″ on a step-deck base) |
| Cargo payload | 42,000–44,000 lb |
The rolling "wagon-top" tarp opens from either side or retracts fully for crane/forklift loading, then seals the freight from weather — no tarping by hand. The frame costs a little capacity versus a bare flatbed.
Straight / Box Truck
Cab and cargo box on a single chassis (no separate trailer) — smaller and far more maneuverable than a semi for city and limited-access deliveries.
| Box length | 12–26′ |
|---|---|
| Box width | 8′ (96") |
| Box height | 8–9′ (96–108") |
| GVWR | 26,000–33,000 lb |
| Cargo payload | ~10,000–12,000 lb |
Heads up: the headline weight on box trucks is usually GVWR, not payload — a 26′ non-CDL truck is ~26,000 lb GVWR but only carries ~10,000 lb of freight. One unit also means a tighter turning radius and easy access to lifts and tight streets; often paired with a liftgate where there's no dock.
Power Only
Just the tractor — you supply the trailer or container. For drop-and-hook moves, repositioning equipment, or pulling your own assets.
| Equipment | Tractor unit only |
|---|---|
| Cab types | Day cab or sleeper |
| Pulls | Your van, reefer, flatbed, or container chassis |
| Typical use | Drop-and-hook, container drayage |
There's no trailer to spec — capacity and dimensions are whatever equipment you provide. Confirm the tractor's fifth-wheel/kingpin and any required endorsements match your trailer.
Heavy haul in depth
How heavy-haul trailers work
Heavy haul is a height problem and a weight-per-axle problem. Trailers drop to clear the legal height; axles get added and spread to stay within axle limits and the bridge formula; past a point, states call it a superload.
Watch
Specialized trailers explained, in 13 minutes
Lowboys and RGNs, how a gooseneck comes off, where a load's weight goes, the bridge formula, spread axles, and what makes a load oversize, overweight or a superload. The sections below follow the same order.
Specialized trailers explained (12:33). Chapters and transcript
Goosenecks
How a removable gooseneck works
Lowboy names the shape: a double drop with a low well between the neck and the rear axles. Fixed, mechanical and hydraulic name the neck. An RGN is a lowboy whose neck comes off, so a machine can drive straight on from the front.
Park the tractor and trailer in a straight line on firm, level ground.
The most common in heavy haul. Cylinders raise and lower the deck, powered by the tractor's own hydraulics (a wet kit) or a small engine in the neck (a pony motor).
Ground-bearing or not
You'll see “non-ground-bearing” on spec sheets. It says how the neck gets its lift.
Capacity
What a 55-ton rating means
On a normal road, less than you'd think. The rating tells you what the frame can hold. The road limit decides what it can carry without a permit.
A strength rating, measured with the weight concentrated in a 12 or 13 ft span of the deck, depending on the builder. It describes the frame, not what the road allows.
Everything above that takes permits and more axles. Added axles don't make the trailer stronger. They make the load legal by spreading it over more of the road.
Weight distribution
Where the weight goes
Think of the trailer as a beam with two supports: the kingpin at the front, which sits on the tractor, and the trailer's axles at the back. A load is shared between them by distance. The closer it sits to one end, the more that end carries.
At 18 ft the drive axles carry 45,338 lb, over their 34,000 lb limit, and the trailer axles carry 38,750 lb. The total is 97,000 lb wherever the machine sits, so no spot on the deck makes this load legal. It needs a permit and more axles.
- Excavator 55,000 lb.
- 40 ft from the kingpin to the center of the trailer axles.
- Tractor wheelbase 20 ft, fifth wheel 1 ft ahead of the drive axles, so 95% of the kingpin load goes to the drives.
- Tractor empty 20,000 lb: 11,000 on the steer, 9,000 on the drives.
- Trailer empty 22,000 lb: 8,000 on the kingpin, 14,000 on its axles.
- Trailer axle limit: 3 axles 9 ft first to last, 42,500 lb by the bridge formula.
In this example the drives drop under 34,000 lb only once the machine sits about 26.7 ft back, and by then the trailer axles carry about 50,700 lb.
Axle limits
Axle limits and the bridge formula
On the Interstate, three numbers set the baseline. Congress set them in 1975 and added the bridge formula at the same time, because a bridge feels how much weight is packed into each foot of truck, not just the total.
- W
- the most weight the group of axles may carry, to the nearest 500 lb
- L
- feet between the first and last axles of the group
- N
- the number of axles in the group
A standard five-axle tractor-trailer needs about 51 ft from the steer axle to the last trailer axle to carry the full 80,000 lb. One exception: two tandems in a row may carry 34,000 lb each when their first and last axles are at least 36 ft apart, where the formula alone gives 66,000.
Adding axles
Spread axles, jeeps, boosters and flip axles
To carry more legally, add axles or spread them out. Build a combination and see how each axle group is held.
| Group | Axles | Spacing | Limit | Why |
|---|---|---|---|---|
| Steer | 1 | one axle | set by state | No federal 12,000 lb limit; states cap it at 20,000 lb or the axle rating |
| Drive axles | 2 | 4 ft 4 in | 34,000 lb | tandem, 52 in apart |
| Trailer axles | 2 | 4 ft 1 in | 34,000 lb | tandem, 49 in apart |
Without a permit the gross stays at 80,000 lb on the Interstate, however many axles. Above that takes an overweight permit from each state on the route.
Why spread axles carry more
Push two axles more than 96 in apart and they stop being a tandem. Each becomes a single axle, good for 20,000 lb, and the pair answers to the bridge formula: 40,000 lb at 10 ft apart, against 34,000 on a closed tandem. Just past 8 ft it is only about 38,000.
- The 36 ft tandem exception doesn't apply to a spread, so a spread-axle trailer passes the formula on its own numbers.
- Spread axles scrub their tires in tight turns.
- Many states limit the distance from the kingpin to the rear axle. California, for example, holds trailers over 48 ft to 40 ft from the kingpin to the rearmost axle.
- States set their own spread rules too, so check every state on the route.
Jeeps, boosters, stingers and flip axles
- Jeep
- An axle group between the tractor and the trailer. The gooseneck hooks to a fifth wheel on the jeep, which takes part of the kingpin weight off the tractor's drive axles.
- Booster, or stinger
- An axle group pinned to the back of the trailer; the name changes by region and builder. Many hold their share with nitrogen: cylinders press against a nitrogen-charged accumulator that acts like a spring, so the axles keep their set load as the road rises and dips.
- Flip axle
- A single axle pinned to the rear that flips up onto the trailer when it's empty, keeping the rig short and the tires off the road.
- Steerable axles
- On long trailers the rear axles can steer, on their own or with hydraulics, so a long combination makes a corner without dragging its tires.
- Not the same thing
- A stinger-steered car hauler is a federal term for a car carrier whose hitch sits behind and below the tractor's rear axle.
Michigan has allowed up to 11 axles and 164,000 lb since 1967, because what wears out a road is the load on each axle, not just the total.
Permits
Oversize, overweight and superloads
A load needs a permit from each state on the route where it passes any of these. Routine permits are often issued online the same day.
Each state sets its own line. Three examples:
160 ft long
201,000 lb gross
135 ft long
17 ft high
over 254,300 lb
gross
Superloads can need route surveys and bridge engineering reviews, and take weeks to approve.
- around 12 ft wide1 pilot car
- around 14 ft wide2 pilot cars
- around 16 ft widepolice escort
Common thresholds; they vary by state. Most states also limit oversize moves to daylight, and many restrict weekends, holidays and rush hours.
Each state's legal limitsThe far end
The biggest rigs
Past the multi-axle lowboy, the trailer starts to wrap around the load.
Simplified models; the green block is the load.
- 294 tons
- the whole superload
- 213 ft
- long, taking two lanes
- ~400 mi
- mostly on I-80, mostly at night
The load: an empty steel tank from a decommissioned prototype reactor.
How to choose
Picking the right trailer
All three are open decks that sit progressively lower so taller freight clears 13′6″. Choose by how tall the load is and how it loads:
- Step deck: up to ~10′ tall, forklift- or ramp-loaded. The everyday choice for freight a flatbed can't clear.
- Double drop (lowboy): ~11′6″–12′ in the low well; crane- or forklift-loaded. For the tallest standard freight.
- RGN: a lowboy whose gooseneck detaches, so the deck becomes a ramp and machinery drives on. For excavators, dozers, and rolling equipment.
The enclosed-vs-open decision comes down to protection, loading, and temperature:
- Dry van — palletized or boxed freight that needs weather protection and loads at a dock.
- Flatbed — oversized or awkward freight loaded by crane/forklift from the side or top; must be tarped and secured.
- Reefer — anything that has to stay cold, frozen, or within a set temperature band.
Not sure? Run the trailer finder or compare LTL vs. truckload.
Regulatory
Legal weight, width & height limits
Trailer choice is mostly about keeping a load legal. Stay inside the limits below and any carrier can haul it; cross a line and you're into permits, escorts, and specialized equipment.
Federal cap on tractor + trailer + freight. A lighter empty weight (or extra axles) leaves more for cargo.
Anything wider needs an over-dimensional permit and, often, escort vehicles.
No federal height limit. Most of the East and Midwest cap at 13′6″, much of the West and the Plains allow 14′ (Arizona stays at 13′6″), Colorado and Nebraska 14′6″, and Alaska 15′. A lower deck buys load height under this line.
A load becomes over-dimensional or overweight when it exceeds any legal limit — too wide, too tall, too long, or too heavy. Permits are issued per state (often $15–$100 each for routine moves; superloads cost more) and may require escorts, daylight-only travel, or specific routing. Picking the right low-deck or multi-axle trailer often keeps a load legal and avoids permits entirely. See your state DOT limits and permit rules for specifics.
FAQ
Frequently asked questions
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