Federal Bridge Formula Weight Calculator

Truck / Axle-Group Presets

Axle Group Inputs

Number of axles in group (N) Whole number, 2–12

Span (L) — outer axle to outer axle Feet, measured to the nearest foot per 23 CFR 658.17

51.0 ft

Drag to explore — inputs above stay in sync

Result

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MAX LEGAL WEIGHT, THIS AXLE GROUP

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L = — ft N = — axles

Formula used (23 CFR 658.17)

W = 500 × ( (L × N) / (N − 1) + 12N + 36 )

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Reference Table — Common Axle Spacings (2-axle groups)

Illustrative subset for a 2-axle group at common spacings, computed live from the same formula above. Full official table (all axle counts, 4–96 ft) is in the FHWA pamphlet linked below.

Span L (ft)	Axles N	Max weight (lb)	Notes

Source: Federal Bridge Gross Weight Formula — 23 CFR § 658.17 and FHWA's "Bridge Formula Weights" pamphlet. Federal single-axle (20,000 lb), tandem-axle (34,000 lb), and gross vehicle weight (80,000 lb) limits are set by 23 U.S.C. § 127.

How this tool works

Federal Bridge Formula Weight Calculator runs entirely in your browser. Inputs are evaluated with rules and constants taken from 23 CFR 658.17 (Freight & logistics). Nothing is uploaded to a server for the calculation itself.

Enter the values that match your load, vehicle, or scenario.
Results update live — treat them as a cited reference, not legal or professional advice.
Open the primary source linked at the top of this page before you rely on a number for compliance.

Use Copy link to share this page (including query parameters when the tool supports them) or Print for a dock/packet copy.

FAQ

What is the Federal Bridge Formula?

It is a federal weight rule (23 CFR 658.17) that limits axle-group weights based on spacing so bridges are not overloaded. States may be stricter.

Does this replace my state’s max weight?

No. Use this as a federal bridge check, then confirm state permits, seasonal postings, and carrier authority limits.

Can I cite this in a claim or customer email?

You can share the link and the underlying public source. Do not present the tool as legal, medical, or insurance advice.