Trucking · scale ticket check
Axle weight and bridge formula checker.
List each axle from the front with its distance from the front axle and its weight. Every consecutive axle group is tested against the federal limits.
Axles
Result
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How it works
For every pair of axles (i, j) in order, the tool takes N = j − i + 1 axles and L = the distance in feet between axle i and axle j, then compares the actual weight on that group with W = 500(LN/(N−1) + 12N + 36) to the nearest 500 lb. It also checks each axle against 20,000 lb, each tandem (axles more than 40 and not more than 96 inches apart) against 34,000 lb, and the total against 80,000 lb. The tandem exception is applied when four consecutive axles form two tandems and the outer axles are at least 36 ft apart: then each tandem may carry 34,000 lb. Worked example, the FHWA five-axle vehicle: axle weights of 12,000 and then 17,000 lb on each of four axles total 80,000 lb. With axles 2 to 5 spread over 35 ft, the group carries 68,000 lb against a 65,500 lb limit, so it fails; at 36 ft or more with two tandems it passes at 68,000 lb.
What this does not decide
This checks the federal limits only. It does not model steer-axle tire ratings, state-specific limits, permits, weight tolerances or enforcement practice, and it takes axle positions you enter at face value. Axle weights from a scale can differ from true weights. This is general information, not legal or compliance advice.
Sources (each retrieved 2026-10-16): FHWA, Bridge Formula Weights (formula, tandem 40 to 96 inch definition, 36 ft exception, five-axle worked examples); 23 CFR 658.17 Weight (20,000 lb single axle, 34,000 lb tandem, 80,000 lb gross).
FAQ
How do I check axle weights against the bridge formula?
Measure the distance between each axle and the front axle, weigh each axle, and compare each consecutive group of axles with W = 500(LN/(N-1) + 12N + 36). This tool does every group for you.
What is the legal weight for a tandem axle?
Federal rules limit tandem axles, spaced more than 40 and not more than 96 inches apart, to 34,000 lb, and a single axle to 20,000 lb.
Why can a truck at 80,000 lb still fail?
The total can be legal while a group of axles carries too much for its spacing. FHWA shows a five-axle truck at 80,000 lb whose rear four axles carry 68,000 lb over 35 ft, above the 65,500 lb allowed.
What does the 36 foot exception mean?
Two consecutive sets of tandems may each carry 34,000 lb if the first and last axle of the group are at least 36 feet apart.
How can I fix a failing axle group?
Move load toward lighter axles, slide the trailer tandem to increase spacing, or reduce the load. FHWA lists removing weight, adding axles or increasing spacing.