Truck axle weight limits: single, tandem, gross and the bridge formula
Four limits govern legal weight on the Interstate system. Miss any one of them and you're overweight — even if the other three pass.
The federal limits
| Limit | Maximum | Applies to |
|---|---|---|
| Single axle | 20,000 lb | Any one axle (e.g. the steer) |
| Tandem axle group | 34,000 lb | Two axles spaced 40–96 inches apart |
| Gross vehicle weight | 80,000 lb | The whole rig |
| Bridge formula | varies | Every group of 2+ consecutive axles |
The first three are easy to remember. The fourth — the Federal Bridge Formula — depends on your axle spacing and is the one that surprises people, because a truck at 80,000 lb gross with a short wheelbase can fail it.
Steer axle reality
Although 20,000 lb is the federal single-axle limit, your steer axle is usually limited lower by its tires: steer tire load ratings commonly cap it around 12,000–13,000 lb. Check the rating on the sidewall — enforcement can, too.
Where state limits differ
Federal limits apply on the Interstate. Off the Interstate, states set their own rules — some allow more on certain roads, many allow less, and permit regimes for oversize/overweight vary widely. If you run the same lanes regularly, learn those states' rules; if your lanes change constantly, use software that tracks per-jurisdiction limits (that's exactly what the LoadLegit platform does).
It's about distribution, not just totals
A 45,000 lb load can be perfectly legal or badly illegal depending on where its weight sits in the trailer. The load's centre of gravity determines how weight splits between your drive and trailer tandems — see weight distribution in a 53′ trailer. To check a scale ticket right now, use the free calculator.
Our axle weight calculator runs the exact Federal Bridge Formula in your browser. The full platform predicts axle loads before you load, computes the slide-to-legal fix, and tracks state limits.
Try the free calculator