Height is measured from the road, not the deck. A 10 ft tall crate on a 5 ft flatbed is 15 ft: over legal in every state. Here are the limits and the trailer math.
31 states set legal height at 13 ft 6 in. 20 allow 14 ft (Alaska, Arizona, Arkansas, California, Colorado, Idaho, Kansas, Missouri, Montana, Nebraska, Nevada, New Mexico, North Carolina, North Dakota, Oregon, South Dakota, Texas, Utah, Washington, Wyoming). Above the limit the load needs a permit, and above about 13 ft 8 in to 15 ft most states add a pole car; above 16 ft, a route survey.
| Trailer | Deck height | Tallest legal load at 13 ft 6 in |
|---|---|---|
| Flatbed | about 5 ft | 8 ft 6 in |
| Step deck | about 3 ft 6 in | 10 ft |
| Double drop / lowboy | about 2 ft | 11 ft 6 in |
| RGN low profile | about 1 ft 2 in | 12 ft 4 in |
So: a flatbed carries a legal load up to 8 ft 6 in tall. A 13 ft 6 in tall load is over height on every trailer made; it needs a permit even on the lowest RGN. The job is picking the deck that keeps the load out of the pole-car and survey tiers, because each tier adds a car for the whole trip, or a survey.
Legal is about the total. Brokers who quote a 10 ft crate on a flatbed because "it fits" end up with a 15 ft load that needs a permit, a pole car in most states, and a route survey in several. The same crate on a step deck is 13 ft 6 in and legal in 51 of 51 jurisdictions. FreightDeck's Truck Builder picks the cheapest trailer that keeps a load legal, and says why. Try it on your load.
FreightDeck estimates permits, escorts, police, route surveys, engineering and the truck rate for your exact load and route, across 50 states and Canada.
Price a load free →13 ft 6 in in most states; 14 ft in 20 (Alaska, Arizona, Arkansas, California, Colorado, Idaho, Kansas, Missouri, Montana, Nebraska, Nevada, New Mexico, North Carolina, North Dakota, Oregon, South Dakota, Texas, Utah, Washington, Wyoming). There is no federal height limit.
About 10 ft to stay legal at 13 ft 6 in, since a step deck's rear deck sits around 3 ft 6 in off the ground.
Most states require a high-pole escort somewhere between 14 ft and 16 ft loaded height; 14 ft 6 in is the most common trigger.