Check Compliance Before You Hit the Scale.
Check truck axle weight compliance against federal limits and the Federal Bridge Formula. Enter axle weights and spacing to instantly see if your 5-axle semi is legal — and get recommendations to fix overweight axles.
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Federal Bridge Law Weight Limits
| Federal gross weight limit | 80,000 lbs | Interstate highways (23 U.S.C. 127) |
| Steer axle limit | 12,000 lbs | single axle, front |
| Drive tandem limit | 34,000 lbs | two axles combined |
| Trailer tandem limit | 34,000 lbs | two axles combined |
| Overweight fine (federal) | Up to $10,000 + $0.04/lb over | per violation |
Sources: Federal Highway Administration Bridge Formula, 23 U.S.C. § 127, FMCSA weight regulations
Quick Answer
The federal gross weight limit is 80,000 lbs — but bridge formula limits based on axle spacing can be more restrictive. A standard 5-axle semi needs at least 51 feet between the steer and rearmost axle to legally carry 80,000 lbs. Enter your configuration and weights below to get an instant federal compliance check.
How the weight rules work, why they exist, and what happens when you break them
Federal axle weight limits are not arbitrary bureaucratic rules — they exist to protect the infrastructure that commerce depends on. A fully loaded 80,000-lb semi truck exerts roughly 9,600 times more stress on a road surface than a passenger car. Bridges built to handle typical traffic loads can fail catastrophically if overloaded. The Federal Bridge Formula was developed specifically to spread that load across enough distance so no concentrated weight cluster exceeds what the underlying structure can handle.
Every commercial vehicle operating on the Interstate Highway System must simultaneously pass three separate compliance tests. Understanding all three — and how they interact — is essential for any driver running near legal weight.
Test 1: Individual Axle and Axle Group Limits
Federal law caps individual axle and axle group weights regardless of the truck's total gross weight. A single axle can carry no more than 20,000 lbs. A tandem axle group (two axles spaced 40-96 inches apart) can carry no more than 34,000 lbs. Your steer axle is capped at 12,000 lbs federally, though some states allow steer axle weights up to 14,600 lbs based on tire load ratings.
These per-axle limits exist because road damage is not proportional to total weight — it's more related to the load per axle. A truck with two 34,000-lb tandem groups does less road damage than the same weight concentrated on fewer axles spaced close together.
You can be under 80,000 lbs gross weight and still be in violation if one axle group is overloaded. This is the scenario that surprises most drivers who get hit with a ticket — they were under gross but ran a heavy trailer tandem.
Test 2: Gross Vehicle Weight
The federal GVW cap is 80,000 lbs for all vehicles operating on the Interstate Highway System. This is the simple sum of all axle weights on your scale ticket. Steer + drive tandem + trailer tandem must not exceed 80,000 lbs. This is the most widely understood limit, but it's not the only one that matters.
Test 3: The Federal Bridge Formula
This is the most nuanced of the three tests and the one most drivers don't fully understand. The bridge formula calculates a maximum allowable weight based on the number of axles and the distance between the extreme axles of a group. The formula is:
W = 500 × [(L × N) / (N − 1) + 12N + 36]
Where W is the maximum weight in pounds, L is the distance in feet between extreme axles, and N is the number of axles in the group. For a standard 5-axle semi with a 51-foot outer bridge, this works out to approximately 79,875 lbs — just under the 80,000-lb federal cap. With a shorter 48-foot outer bridge, the bridge formula allows only about 78,000 lbs gross, meaning your effective weight limit is 2,000 lbs below the statutory maximum.
The practical implication: a driver running a short trailer or a compressed axle configuration may be weight-legal on individual axles and under 80,000 gross weight, but still in violation of the bridge formula.
Fixed weigh stations use WIM (Weigh-in-Motion) sensors embedded in the pavement approach to capture your approximate weight before you reach the scale. If WIM shows you're potentially heavy, you're directed to pull into the scale. PrePass and Drivewyze electronic screening bypass systems let compliant carriers skip many fixed scales — but only after their historical compliance record clears automated review.
If you're flagged for inspection, the portable scales measure each axle group individually. The enforcement officer will check all three compliance tests: individual axle limits, gross weight, and the bridge formula based on your measured axle spacing. A CSA (Compliance, Safety, Accountability) overweight violation not only generates a fine but adds points to your safety score, affecting your ability to clear PrePass screens in the future.
A CAT scale ticket shows three or four numbers depending on your configuration. For a standard 5-axle: the first number is your steer axle weight, the second is your drive tandem, the third is your trailer tandem, and the bottom number is your gross vehicle weight (which should equal the sum of the three above). The ticket also shows your outer bridge measurement — the distance from center of steer axle to center of rearmost axle. This is the L value you need for the bridge formula calculation.
When individual axle groups are near or over limit, tandem sliding is typically the first adjustment to make. Moving your trailer tandems forward (toward the cab) transfers weight from the trailer axle group to the drive axle group. Moving them back transfers weight from drives to trailer axles. Each notch — approximately 6 inches of movement — shifts roughly 350 to 500 lbs between axle groups.
The exact transfer rate depends on cargo distribution, but 400 lbs per notch is a reliable working estimate for most loads. If your trailer tandem reads 34,800 lbs (800 lbs over), sliding the tandems forward two notches should bring you down approximately 800 lbs, putting you around 34,000 lbs or slightly under.
Always re-scale after any adjustment. The weight transfer rate is an approximation — actual results vary with load distribution, trailer geometry, and fifth wheel position. Never assume a calculation puts you in compliance without verifying on a certified scale.
Why the same load can be legal in Texas and illegal in California
The federal limits — 80,000 lbs GVW, 34,000 lbs tandem, 20,000 lbs single axle — apply specifically to the Interstate Highway System. Once you exit the Interstate onto state or local roads, you're operating under state law, and state weight limits vary significantly from the federal baseline.
This creates a compliance challenge that catches experienced drivers off guard: a load that's perfectly legal for your entire highway run can suddenly be out of compliance the moment you turn off the exit ramp toward your delivery.
Michigan is the most notable outlier in American weight law. The state allows significantly higher weights on its state highway system than federal law allows on the Interstates. Under Michigan's "extra-axle" system, a properly configured vehicle with enough axles can legally operate at up to 164,000 lbs — more than twice the federal Interstate limit. Michigan's road system was built with this in mind, and the state's manufacturing economy historically depended on heavy equipment transport.
For drivers operating in Michigan, this means the calculus is entirely different from the rest of the country. Loads that would require an overweight permit on most state highways can move legally in Michigan on certain routes under the right axle configuration.
California is the strictest enforcing state in the country. The California Highway Patrol operates fixed weigh stations at nearly every significant highway corridor and enforces the federal limits with near-zero tolerance. The state also enforces its own more restrictive limits on some state routes. Overweight fines in California escalate steeply with the amount overweight — a 10,000-lb overweight violation can result in fines exceeding $10,000, plus mandatory offload if the violation is significant enough.
Illinois uses weight-based fine schedules that can make a single overweight stop extremely expensive. The state also prosecutes overweight violations more aggressively as cumulative violations — a carrier's second or third violation in a period can trigger enhanced penalties.
Georgia has a mandatory offload policy for vehicles significantly overweight. If you're pulled into a Georgia scale house and found to be substantially over limit, you may be required to stay until you offload enough cargo to come into compliance — regardless of how long that takes or how much it costs in detention.
Some states build a small tolerance into their enforcement policy. Several midwestern agricultural states allow tandem weights up to 36,000 lbs on state highways, which effectively gives drivers a small buffer above the federal 34,000-lb limit when operating on those routes. These tolerances are route-specific and sometimes seasonal — many states temporarily increase weight limits during grain harvest season to accommodate the agricultural transport demand.
Always verify current weight limits for your specific route rather than relying on general state reputation. Weight limits change, and a route that had a tolerance last year may have been modified.
When planning a multi-state route, the most restrictive state's limits govern that portion of your trip. You can't average out your compliance — you need to be legal in every state you cross. A load that's 79,500 lbs gross is fine in most states but would be over the bridge formula limit in a state with short-bridge infrastructure if your axle configuration isn't spread far enough.
The practical approach for regular runs is to know the binding constraint for each lane you operate. If you run a regular Texas-to-California corridor, you need to know California's limits and stay inside them for the entire load, even on portions of the run where Texas limits would allow more.
When you legitimately need to haul more than standard weight limits allow — a construction equipment move, oversized machinery, or a shipper with dense cargo — overweight permits are the legal mechanism. Permits are issued by individual states and typically cost $25 to $500 per state depending on the weight overage, route complexity, and whether a route survey is required.
Critically, an overweight permit authorizes gross weight above the standard limit — but it does not override individual axle group limits. A permit for 95,000 lbs gross doesn't mean you can run 40,000 lbs on a tandem. The per-axle limits are often separately negotiated in the permit terms, and you may need additional axles to distribute the weight legally.
Permit requirements vary significantly: some states issue permits electronically within minutes; others require multi-day processing with route surveys and escort vehicle requirements for very heavy loads.
The single best practice for avoiding overweight violations is to scale your loaded truck before leaving the shipper's facility. Many shipping docks have certified scales on premises, and a few minutes verifying your weight before you leave can save hours of delay at a weigh station, hundreds to thousands of dollars in fines, and the CSA score impact of a weight violation.
If the shipper's scale isn't available, stop at the nearest CAT scale — they're at most major truck stops — before you get on the highway. Knowing your numbers before you hit an enforced weigh station is the only way to handle a potential compliance issue before it becomes a citation.
A weight violation on your CSA record follows you for two years and drives up insurance. Our dispatchers confirm load weight documentation before you ever back into a dock.
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