Flatbed trailer dimensions and weight limits

Before you book any flatbed load, two questions decide whether it is legal: does it fit, and is it too heavy? This guide gives the flatbed trailer dimensions for the open-deck trailers we dispatch, the federal size and weight limits with their sources, and a simple way to work out your legal payload.

Dimensions by trailer type

Figures are typical and vary by maker, model and load. Two current step deck examples: a 2026 Utility 4000AE listing shows an 11 ft upper deck at 59-5/8 in and a lower deck at 40-1/4 in (Truck Paper), and a Trail King TK85 listing shows a 36 in loaded lower deck (AutoTrader.ca). A standard flatbed deck sits at about the same height as a step deck's upper deck. Conestoga figures are from Inbound Logistics.

Measure your own deck height loaded and empty, and use your numbers when you check a load.

Legal size limits

Width. 102 in on the National Network (23 CFR 658.15). Anything wider is oversize.

Length. States must allow semitrailers of at least 48 ft in a tractor-semitrailer combination on the National Network, and they cannot cap the overall length of that combination (23 CFR 658.13). 53 ft trailers are widely allowed, but kingpin-to-axle rules vary by state, so check yours.

Height. There is no federal height limit. States set it, most commonly at 13 ft 6 in, with some allowing 14 ft or more. Plan to the lowest limit on your route.

Overhang. States set rear and front overhang limits. Federally, a load projecting more than 4 in past either side or more than 4 ft past the rear must carry red or orange fluorescent flags at least 18 in square at its extremities (49 CFR 393.87).

Weight limits and the payload formula

On the Interstate system the federal limits are (23 CFR 658.17):

• 80,000 lb gross vehicle weight.
• 20,000 lb on a single axle.
• 34,000 lb on a tandem axle group.
• The bridge formula, which limits weight on any group of axles based on how far apart they are.

Your legal payload is simple:

Legal payload = 80,000 lb - (empty tractor + empty trailer + fuel + driver + gear)

EXAMPLE. A tractor at 19,000 lb, a flatbed at 10,500 lb, and 3,500 lb of fuel, gear, tarps and driver come to 33,000 lb. Legal payload: 80,000 - 33,000 = 47,000 lb. Weigh your truck empty with full fuel and your normal gear for the real figure.

Flatbed trailer weight distribution

Hitting 80,000 lb gross is not enough; each axle group has to stay legal too. With a heavy, short load like a steel coil, where you place it on the deck decides how the weight splits between your drives and the trailer tandem. Too far forward overloads the drives; too far back overloads the trailer axles.

Practical habits:

• Ask the shipper for the exact weight of each piece and where it will sit.
• Know roughly how your truck splits weight at different positions, and slide the trailer tandem if you have one.
• Scale the load at the first certified scale and adjust before you go far.

When you need a permit

You need state oversize or overweight permits when a load:

• Is wider than 102 in.
• Is taller than the height limit of any state on the route.
• Is longer than the state allows or overhangs past its limits.
• Pushes gross or axle weights over the legal limits.

Permits are issued per state and per trip or by annual permit, and they come with routing, travel-time and escort rules. Many oversize flatbed loads can avoid permits altogether on a step deck, because of the lower deck height.

Put the numbers to work

When a load is posted, check it against this guide, then run the rate. The flatbed rate calculator shows what a load really pays per mile, and our flatbed rates guide gives current averages. New to open deck? Start with what flatbed trucking is, see where flatbed loads come from, and read how to start a flatbed business for the gear and setup checklist.