Start from a common rig
Axles, front to rear
Up to 13 axles. Positions must increase front to rear; the calculator refuses to compute on impossible geometry rather than returning a number.
State limits
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What this answers, and where the answer stops
A weight verdict is not a route clearance. The three facts below are the whole boundary.
The federal bridge formula on every group of two or more consecutive axles, plus the flat federal 20,000 lb single-axle, 34,000 lb tandem and 80,000 lb gross limits — and, for the 32 states with a jurisdiction file, that state's own published single-axle, tandem and gross figures with the document behind each one.
Seasonal (spring thaw) restrictions, which are posted road by road; local bridge postings; toll, bridge and city authorities that issue their own permit inside the same state; and permit fees. Any one of them can make a rig that passes here illegal on a specific route. A state with no jurisdiction file is checked against the federal limits only, and the result says so.
Nothing, and no account. Every input is in the request and every limit is compiled in, so the page renders and the endpoint answers with the database unreachable, and neither calls anything billable.
Three checks, in order
Describe the rig
Position is the distance in feet from the steer axle, measured centre to centre; weight is what that axle actually carries, not its rating. Start from one of 4 real configurations and edit from there.
Every group gets enumerated
Each single axle, then every group of two or more consecutive axles against the bridge formula — all N(N−1)/2 of them, not the obvious three — then the whole vehicle against the federal gross limit. The count is returned so you can see it rather than take it on trust.
Add a state, and read the citations
Pick a state and three more lines appear: heaviest single axle, heaviest tandem group and gross, each against that state's own published figure, each linking to the document and carrying that document's revision date.
What the verdict lines actually mean
The measurement is derived, not typed
Each state line compares one measurement from your rig against that state's published limit, and the measurement is computed rather than asked for. The heaviest single axle is the heaviest one you entered; the heaviest tandem group is the heaviest group spanning 8 ft or less — the span that makes a group a tandem under federal law.
The headroom column is the one to read. A pass/fail says nothing about whether shifting a thousand pounds of freight breaks the rig, and the group with the least headroom is the one that decides.
- States with a jurisdiction file
- 32
- State limits checked per rig
- 3
- Tandem span, federal
- 8 ft or less
Two dates on every line, not one
Every limit links to the document it came from and carries two dates: the revision date the document itself states, and the date we retrieved it. They are different facts, and a single "last updated" stamp would hide the difference — a schedule downloaded this morning can still be five years old.
Where two of a state's own documents disagree, the line shows both readings with their citations and the verdict reads "cannot tell". That is the honest answer, and the one that sends the question to the permit office rather than to a coin toss.
- Federal single axle
- 20,000 lb
- Federal tandem axle
- 34,000 lb
- Federal gross weight
- 80,000 lb
Questions
What is different from the bridge formula calculator?
This one brings a state's own limits into the answer. Pick one of the 32 covered states and the heaviest single axle, the heaviest tandem group and the gross are checked against that state's published figures, each verdict line carrying the rule and its revision date.
Why does a state limit sometimes say "sources disagree"?
Because two of that state's own official documents give different figures and both are in effect. Neither has been adopted here — the line shows both with their citations and the verdict reads "cannot tell", which is the honest answer and the one that sends the question to the permit office rather than to a coin toss.
What does the headroom column tell me?
How much more that group could carry before it is over. A pass/fail says nothing about whether shifting a thousand pounds of freight breaks the rig, and the group with the least headroom is the one that decides how the load can be re-secured.
Does a state pass mean the whole route is legal?
No. Seasonal weight restrictions are posted road by road and can make a legal axle group illegal on a specific route in March, and local bridge postings are not in any statewide figure. Both are named in the "what this does not answer" list on the result.