Every conversation about oversize loads starts with the wrong assumption: that "legal" is one number. It is several numbers, they interact through a formula, and the moment you exceed any of them the movement becomes a state-by-state permitting exercise rather than a federal one.
Knowing which limits are federal and which are not is the difference between planning a route and discovering a problem at a scale house.
The federal weight limits on the Interstate System
From 23 CFR 658.17: the maximum gross vehicle weight is 80,000 pounds except where a lower gross weight is dictated by the bridge formula; the maximum gross weight on any one axle, including any one axle of a group, is 20,000 pounds; and the maximum gross weight on tandem axles is 34,000 pounds.
The same section limits what states may do in the other direction. States may not enforce weight limits on the Interstate System below 20,000 pounds on a single axle, 34,000 pounds on a tandem axle, or the weights derived from the bridge formula up to 80,000 pounds, including all enforcement tolerances. Steering axles may not be limited to less than 20,000 pounds or the manufacturer’s rating, whichever is lower.
Two carve-outs are worth knowing. States may issue special permits without regard to axle, gross, or bridge formula requirements for nondivisible vehicles or loads — which is the legal basis for the whole permitting system. And a vehicle using an auxiliary power or idle reduction unit may be allowed up to an additional 400 pounds, subject to written certification of the unit’s weight and proof that it is functional.
The bridge formula, and why five axles is not automatically 80,000
The formula appears in 23 U.S.C. 127(a)(2) as W = 500 ( LN/(N−1) + 12N + 36 ), where W is the maximum weight on a group of consecutive axles, L is the distance in feet between the first and last axle of the group, and N is the number of axles in the group. The regulation adds that two consecutive sets of tandem axles may carry 34,000 pounds each if the overall distance between the first and last axle is 36 feet or more — and that in no case may total gross weight exceed 80,000 pounds.
Worked illustration, computed from the formula: a five-axle combination with 48 feet between the first and last axle yields W = 500 × ( (48 × 5) / 4 + 12 × 5 + 36 ) = 78,000 pounds. Not 80,000. A rig can be under every individual axle limit, under the 80,000-pound cap, and still be illegal because the axle spacing does not support the load. Stretching the wheelbase is what buys the last 2,000 pounds.
This is why "we are under 80,000" is not an answer. The bridge formula governs every group of consecutive axles, and it is the limit that catches short-wheelbase configurations.
What is NOT federal
Two widely repeated "federal limits" do not exist in the regulation.
There is no federal height standard. 23 CFR Part 658 addresses length, width, and weight, and contains no height section. Height limits are set by states, which is why the common figures of 13 feet 6 inches or 14 feet vary by where you are.
There is no federal maximum trailer length. What 23 CFR 658.13 does is set floors that states may not go below — including 48 feet for a semitrailer and 28 feet for each trailer in a twin combination. That is a minimum a state must allow, not a maximum it must impose, which is the opposite of how it is usually described. The frequently cited 53-foot figure is a matter of state law, not a federal cap.
Width is federal on the designated system: 102 inches is the standard, which is where "102-inch legal width" comes from.
Permits are a state matter, and the variation is large
Because permits are issued by states, nearly everything about them varies: fees, validity, permitted routes, curfews and travel-time restrictions, escort and pilot-car requirements, and the threshold at which a load becomes a superload requiring individual engineering review.
The variation is not marginal. Verified superload thresholds range from 200,000 pounds in Washington to 254,300 pounds in Texas. Even the phrase "single-trip permit" means different things: 3 days in Washington, one continuous movement in Texas, ten days in Florida.
The practical consequence for a multi-state move is that you are not buying a permit — you are buying a permit per state, each with its own route approval, and the most restrictive state on the route governs the schedule. Oregon states the timing rule directly: an oversize or overweight vehicle must obtain a variance permit before entry when the operation originates outside Oregon, and before operating when it originates inside.
Frequently asked questions
What is the federal weight limit for trucks?⌄
Why am I overweight if I am under 80,000 pounds?⌄
Is there a federal height limit for trucks?⌄
Is 53 feet the federal trailer length limit?⌄
What is a superload?⌄
Related guides
More in Carrier Credentials & Federal Compliance
Official sources
- 23 CFR 658.17 — weight (eCFR)
- 23 CFR 658.13 — length (eCFR)
- 23 U.S.C. 127 — vehicle weight limitations
- FHWA — bridge formula weights
Agency rules, fees and contacts can change — confirm current requirements with the agency before acting. This guide is general information for truckers, not tax or legal advice.