Federal Bridge Formula & Axle Weight Calculator
Enter axle count and spacing to get the maximum legal weight for that axle group under the federal bridge formula, alongside the federal single, tandem and gross limits.
100% free · no signup · nothing to install
The federal bridge formula (23 CFR 658.17) limits the weight any group of axles can carry based on how far apart they are: W = 500 × (LN ÷ (N−1) + 12N + 36). Federal limits also cap single axles at 20,000 lb, tandems at 34,000 lb and gross vehicle weight at 80,000 lb on the Interstate.
- • Formula result: 79,500 lb
- • Federal Interstate gross cap: 80,000 lb
- • Single axle: 20,000 lb · Tandem axle: 34,000 lb
State limits on non-Interstate routes and grandfathered corridors can differ. Anything above these limits needs an oversize/overweight permit for every state you cross.
Over the limit? You need permits, not luck.
We handle oversize/overweight permits, apportioned plates and state authorities across every state you run, so a heavy load doesn't turn into a fine and a delayed delivery.