Federal size and weight limits, and the one there isn't
Gross, single and tandem weights, the bridge formula, width and length on the National Network — and the dimension the federal government does not regulate at all.
- Author
- Relay Dispatch Desk
- Published
- 18 Aug 2026
- Verified
- 15 Aug 2026
- Re-checked
- annually
Key takeaways
- 80,000 lb gross, 20,000 lb on a single axle, 34,000 lb on a tandem — all subject to the bridge formula.
- 102 inches wide on the National Network, and states must allow a 48 ft semitrailer as a floor, not a cap.
- Twin trailers are 28 ft each.
- There is no federal height limit at all. Height is a state number every single time.
Four numbers cover most of what a driver needs, and the fifth thing worth knowing is which dimension has no federal number behind it at all.
Weight is capped twice
The axle and gross limits are one cap. The bridge formula is the other, and it is the one that catches people: it relates the weight carried on a group of axles to the distance between them, so a legal gross weight can still be an illegal distribution. FHWA publishes the formula with worked examples.
Dimensions
| Dimension | Federal position | What it means for you |
|---|---|---|
| Width | 102 in on the National Network | A ceiling, uniform across states |
| Semitrailer length | States must allow at least 48 ft | A floor — many states allow more |
| Twin trailers | 28 ft each | A floor, same logic |
| Overall combination length | No federal limit for tractor-semitrailer | Set by the state |
| Height | No federal requirement whatsoever | Entirely state law — check before you route |
Sources
- FHWA · Bridge Formula Weights (FHWA-HOP-19-028) · FHWA-HOP-19-028 · accessed 15 Aug 2026
- FHWA · Federal Size Regulations for Commercial Motor Vehicles (FHWA-HOP-04-022) · FHWA-HOP-04-022 · accessed 15 Aug 2026
Re-verified annually. Educational summary — the regulation controls. Not legal advice.
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