← TRACKS 4 TRUCKERS™Driver Resources

KNOW BEFORE YOU ROLL

Know your limits.
Axle weight & bridge rules.

Choose any state and your equipment. Review its rules, then enter scale weights to check axle groups.

Coverage: State-by-state source guides for all 50 states and DC, with equipment and axle guidance. Automatic weight calculations currently use the federal Interstate baseline or California standard table. Other state tables, exceptions and permit eligibility are explained where researched but are not fully calculated. Read the selected state’s scope before using a result.
1 · Your truck and route

Body style and cab are profile details. Actual axle locations, weights and applicable rules control the calculation. Use the current slider position; a spread preset does not establish truck legality.

Trailer dimensions

Enter dimensions for the state rules review. Kingpin rules may measure to the rear axle or the center of a tandem; enter both when known. Lifting an axle does not automatically change the legal measurement.

2 · Axles, front to back

Enter the scale weight for each axle, not a tandem total. Measure axle spacing center to center. Feet and inches are separate: 10′2″ = 122 inches; 102 inches = 8′6″.

Lift and sliding axle guidance

Sliding: enter the actual spacing and kingpin measurement after moving the slider.

Lift / retractable: mark each lift axle and whether it is raised. A raised axle must have zero road weight and is excluded from weight-bearing groups. Its physical spacing is retained. Reweigh all grounded axles after raising or lowering; this tool does not redistribute loads automatically.

California permits: Caltrans says lift axles do not qualify for extralegal weight and must be raised in that permit context. That statement is not a general instruction to raise a lift axle during ordinary operation. Caltrans permit FAQ ↗

California legal treatment of a particular retractable assembly and its kingpin measurement requires confirmation; no automatic compliance conclusion is issued for lift-axle profiles.

3 · Additional limits, if known

Posted axle/group restrictions, tire-width rules, seasonal limits, permits, manufacturer limits not entered, and route access still require review. Do not substitute a posted axle-group limit for a gross limit.

Rules, sources & coverage

Rules reviewed October 20, 2026. Sources can change; check the official guidance before travel. Results use your entered measurements, not a live inspection or bridge-rating database.

Federal baseline

Ordinary Interstate screening: 20,000 lb single axle, 34,000 lb tandem group and 80,000 lb gross, subject to every consecutive axle group's bridge-formula limit. Closely spaced groups use the applicable single/tandem ceiling. Eligible consecutive tandems with at least 36 ft outer spacing use the 68,000 lb exception. Grandfather rights and special allowances require separate review.

Formula: W = 500 × [L × N ÷ (N − 1) + 12N + 36], rounded to the nearest 500 lb. L is outer-group spacing in feet and N is the number of grounded axles.

FHWA formula, definitions and worked examples ↗
California: spreads, kingpin distance and scope

Standard mode uses Caltrans's CVC 35551 table for groups of 2–6 axles, with distances rounded to the nearest whole foot (six inches rounds up), plus single-axle and gross checks. The alternate CVC 35551.5 method and special exceptions are not evaluated. Groups outside the verified table require review.

A two-axle group at 10′2″ rounds to 10 ft in this table and has a 40,000 lb group ceiling, still limited by each axle, tires, other groups and gross weight. This does not establish trailer-length or route compliance.

For the screened STAA tractor/semitrailer configuration, a trailer over 48 ft and no longer than 53 ft needs a kingpin-to-rearmost-axle distance no greater than 40 ft with two or more rear axles, or 38 ft with one. STAA trailers no longer than 48 ft have no KPRA maximum in Caltrans's quick-guide category. California Legal combinations and local routes need their own access review.

Caltrans weight tables ↗ · California lengths and route networks ↗ · Lift axles and permits ↗

All 50 states: what the state guide does

Select a state and use “Show my state & equipment rules” to see its sourced road scope, standard reference ceilings, bridge method and equipment notes. Reference ceilings must be read with their conditions; they do not replace the state’s complete weight table. Missing or conflicting rules are marked for review. The separate axle-group calculator is explicitly labeled federal baseline or California standard table.

Permits, special commodities, seasonal limits, local bridges and exact route access may need agency confirmation. State guide research checked October 20, 2026; older official publications are identified in their source titles.