Flatbed Weight Limits: Axle Configurations & Bridge Formula
Weight distribution on a flatbed trailer is more complex than with enclosed trailers because freight placement is visible and variable. Unlike a dry van where freight is evenly distributed by pallets, flatbed loads often involve concentrated heavy items like steel coils, machinery, or lumber bundles that can overload specific axles. Understanding axle weight limits and the bridge formula keeps you legal, safe, and out of the weigh station penalty box.
80,000 lbs
Federal GVW Limit
12,000 lbs
Steer Axle Limit
34,000 lbs
Tandem Axle Limit
~48,000 lbs
Max Flatbed Payload
O Trucking Editorial Team
Trucking Industry Experts
Fact-Checked by O Trucking Dispatch Team
5+ years managing flatbed loads, weight compliance, and permit coordination
This article was written by the O Trucking editorial team with 9+ years of combined trucking industry experience. Learn more about us.
O TruckingFlatbed Weight Limits by Axle: Bridge Formula (2026)
Federal Weight Limits
The Federal Highway Administration (FHWA) sets baseline weight limits for commercial vehicles on the Interstate Highway System. These are the maximums unless a state has received an exemption for higher limits on specific routes.
| Weight Category | Federal Limit | Notes |
|---|---|---|
| Gross Vehicle Weight (GVW) | 80,000 lbs | Total weight of truck + trailer + freight |
| Single Axle | 20,000 lbs | One axle with single or dual tires |
| Tandem Axle (2 axles) | 34,000 lbs | Two consecutive axles spaced 40-96 inches apart |
| Steer Axle (practical limit) | 12,000-14,000 lbs | Limited by tire rating, not federal law specifically |
GVW vs Axle Limits
Axle Configurations Explained
Flatbed trailers come in several axle configurations, each with different weight capacities and applications:
Single Axle Flatbed
A flatbed trailer with one axle. Single axle flatbeds are relatively rare in OTR trucking and more common in local delivery and agriculture. The single axle limits the trailer to approximately 20,000 lbs on that axle, resulting in a maximum payload of roughly 25,000-30,000 lbs depending on tractor weight.
Common use: Local delivery, farm equipment, light construction materials.
Tandem Axle Flatbed (Most Common)
The standard OTR flatbed configuration with two axles. Tandem axle flatbeds are allowed 34,000 lbs on the trailer tandems, providing approximately 45,000-48,000 lbs of payload capacity within the 80,000 GVW limit. The tandems are typically slidable, allowing the driver to redistribute weight between the drive axles and trailer axles.
Common use: The vast majority of flatbed freight: lumber, steel, pipe, machinery, building materials.
Tridem Axle Flatbed (Spread Axle / Tri-Axle)
A flatbed trailer with three axles. Tridem configurations increase the legal weight capacity on the trailer to approximately 42,000-50,000 lbs on the trailer axle group (varies by state), allowing gross weights up to 90,000-105,500 lbs with the proper permits in some states. The additional axle distributes weight over a larger area, reducing the stress on bridges and roads.
Common use: Heavy haul flatbed work: heavy machinery, large steel fabrications, concrete products, overweight loads requiring extra axles instead of permits.
Spread Axle Configuration
When axles are spaced more than 10 feet apart (typically on a step deck or RGN), each axle is treated as a single axle for weight calculations instead of a tandem. This allows 20,000 lbs per axle, totaling 40,000 lbs for two spread axles — 6,000 lbs more than the 34,000-lb tandem limit. Spread axle configurations are popular for heavy flatbed loads.
Common use: Heavy flatbed and step deck loads that need extra payload capacity without adding a third axle.
Bridge Formula Breakdown
The Federal Bridge Formula determines the maximum weight allowed on any group of consecutive axles based on the number of axles and the distance between them. The formula exists to protect highway bridges from concentrated loads that could cause structural damage.
The Bridge Formula
W = 500 x [(LN / (N-1)) + 12N + 36]
- W = Maximum weight in pounds on a group of axles
- L = Distance in feet between the first and last axle in the group
- N = Number of axles in the group
Here is what the bridge formula allows for common flatbed axle configurations:
| Axle Group | Axle Spacing | Max Weight (Bridge Formula) | Max Weight (Federal Cap) |
|---|---|---|---|
| 2 axles (tandem) | 4 ft | 34,000 lbs | 34,000 lbs |
| 2 axles (spread) | 10+ ft | 38,000-40,000 lbs | 40,000 lbs |
| 3 axles (tridem) | 8-10 ft | 42,000-50,000 lbs | Varies by state |
| 5 axles (full rig, steer to trailer) | 51 ft | 80,000 lbs | 80,000 lbs |
The 51-Foot Rule
State Weight Limit Differences
While 80,000 lbs GVW is the federal standard on Interstate highways, many states have different limits on non-Interstate roads. Some states allow higher weights with permits or on specific routes. Here are notable variations:
| State | GVW Limit (Interstate) | GVW Limit (Non-Interstate) | Notes |
|---|---|---|---|
| Michigan | 80,000 lbs | 164,000 lbs | Highest in US (on designated routes with proper axle config) |
| Nevada | 80,000 lbs | 129,000 lbs | With additional axles on state routes |
| Utah | 80,000 lbs | 129,000 lbs | On designated routes with proper permits |
| Texas | 80,000 lbs | 84,000 lbs | On non-Interstate roads with permit |
| Most States | 80,000 lbs | 80,000 lbs | Same on all roads; overweight permits available |
Permits Do Not Override Safety
Weight Distribution for Flatbed Loads
Proper weight distribution is critical for flatbed loads because the freight placement is entirely in the driver's control. Here are the key principles:
Center of gravity placement — Position the heaviest items between the drive axles and the trailer tandems. The center of the load should be slightly forward of center on the trailer. This distributes weight evenly between drive axles and trailer tandems, keeping both under their respective limits.
Slide tandems to balance — If your drive axles are heavy, slide trailer tandems forward to shift weight off the drives and onto the trailer axles. If trailer tandems are heavy, slide them rearward. Each hole you slide the tandems moves approximately 300-500 lbs between the axle groups.
Avoid concentrated point loads — Heavy items should distribute their weight across as much of the trailer deck as possible. Use dunnage and blocking to spread the load. A 40,000-lb steel coil sitting on a 3-foot section of deck creates a massive concentrated load that can exceed axle limits even when total weight is legal.
Check steer axle weight — Flatbed drivers sometimes overlook steer axle weight. Loading heavy freight too close to the front of the trailer increases steer axle weight. Your steer axle tires are typically rated for 12,000-14,000 lbs. Exceeding this rating causes tire failure and unsafe steering response.
Side-to-side balance — Flatbed loads must also be balanced left to right. An unbalanced side-to-side load increases the risk of rollover on curves and ramps. When loading multiple items, alternate placement to keep weight centered. Use a level or visual inspection to verify the trailer is sitting even.
Common Violations & Penalties
Overweight violations are among the most common and expensive citations for flatbed drivers. Here are the violations that get flatbed drivers in trouble:
Axle Overweight ($100-$10,000+ per axle group)
The most common flatbed violation. Individual axle groups exceed their limit even though total GVW may be legal. Penalties are assessed per pound over the limit, and the driver is typically held at the weigh station until weight is removed or redistributed. Repeat violations in some states lead to CDL points and potential license suspension.
Gross Overweight ($250-$15,000+)
Total vehicle weight exceeds 80,000 lbs (or the state limit) without an overweight permit. Fines escalate rapidly with the amount over. Some states fine per-mile over the limit from the point of origin to the weigh station. Being 10,000+ lbs overweight is considered a serious violation with severe penalties.
Bridge Formula Violation ($200-$5,000+)
Weight between axle groups exceeds the bridge formula allowance, even if individual axle limits and GVW are legal. This violation catches drivers who have their tandems slid too close together or who have a short wheelbase. The fix is usually to slide tandems to increase the distance between axle groups.
Bypassing a Weigh Station ($300-$1,000+)
Driving past an open weigh station without stopping is a separate violation regardless of whether you are overweight. Law enforcement treats weigh station bypass seriously because it suggests the driver knows they are overweight. Fines vary by state but start at $300 and can include impoundment.
How to Weigh Properly at CAT Scales
Weighing at a CAT scale before hitting a weigh station is the best way to avoid overweight violations. Here is the proper process for flatbed loads:
Position your axles correctly — Pull slowly onto the scale. Place your steer axle on the first platform, drive axles on the second, and trailer tandems on the third. Make sure your axles are centered on each platform. If you straddle two platforms, the readings will be inaccurate.
Read each axle group separately — The CAT scale printout shows steer, drive, and trailer axle weights individually plus the total. Check each number against the legal limit. Being under 80,000 total but over 34,000 on your drives is still a violation.
Adjust and reweigh — If any axle group is overweight, slide your tandems to redistribute weight. Sliding tandems forward shifts weight from the trailer axles to the drive axles. Sliding them back does the opposite. After adjusting, reweigh to confirm all axle groups are legal. CAT scales offer a free reweigh if done within the same visit.
Keep your scale ticket — A CAT scale ticket showing you are legal on all axles is your best defense if a weigh station shows a slightly different reading. The CAT scale "weigh my truck" guarantee means they will pay any overweight fine if their scale was wrong. Always weigh at a CAT scale before a known weigh station.
Use the Weigh My Truck App
The Bottom Line
Weight compliance is a daily responsibility for flatbed drivers. Unlike dry van loads where weight is typically pre-calculated by the shipper, flatbed drivers must actively manage weight distribution based on freight placement, tandem position, and the bridge formula.
The cost of an overweight violation — $500 to $10,000+ in fines, potential CDL points, hours of delay at the weigh station, and possible out-of-service orders — far exceeds the $15 cost of a CAT scale weigh. Weigh every heavy load before your first weigh station, and know how to slide tandems to redistribute weight when needed.
For more on flatbed operations, see our flatbed load securement guide, sliding tandems guide, and how to avoid overweight violations.
Flatbed Weight Limits FAQ
Common questions about flatbed weight limits, bridge formula, and axle weights
How much weight can a standard flatbed trailer carry?
A standard 48-foot or 53-foot flatbed trailer with a tandem axle configuration can carry approximately 48,000 pounds of freight while staying under the federal 80,000-pound gross vehicle weight limit. The tractor typically weighs 17,000 to 20,000 pounds and the empty trailer weighs 12,000 to 15,000 pounds, leaving 45,000 to 48,000 pounds of payload capacity. However, the actual legal payload depends on axle weight limits and the bridge formula, not just gross weight. Improperly distributed freight can put you over axle limits even when your total weight is under 80,000 pounds.
What is the bridge formula and how does it apply to flatbed loads?
The Federal Bridge Formula (also called Bridge Weight Formula or Formula B) calculates the maximum weight allowed on any group of two or more consecutive axles based on the number of axles and the distance between the first and last axle in the group. The formula is W = 500 times the quantity (LN divided by N minus 1 plus 12N plus 36), where W is maximum weight in pounds, L is distance in feet between outer axles, and N is number of axles. For flatbed drivers, this means you must consider not just total weight but how it is distributed across the distance between axles. A concentrated load in the center of the trailer might exceed the bridge formula even if total weight is under 80,000 pounds.
What are the penalties for an overweight flatbed truck?
Overweight penalties vary by state but generally include fines ranging from $100 for being 1,000 pounds over to $10,000 or more for extreme overweight violations. Many states fine on a per-pound-over basis, typically $0.05 to $0.20 per pound over the limit. Being 5,000 pounds overweight in a strict state could cost $500 to $1,000 in fines. Some states also add points to your CDL, charge for the overweight inspection time, and can impound the truck until weight is removed. Repeat offenders face increased fines and potential loss of operating authority. The driver, carrier, and sometimes the shipper can all be held liable.
How do I properly weigh a flatbed load at a CAT scale?
At a CAT scale, pull onto the scale platform slowly and position your steer axles on the first platform, drive axles on the second, and trailer tandems on the third. Stop when directed by the scale display or operator. The scale reads each axle group separately, which is critical for flatbed loads because weight distribution matters as much as total weight. If any axle group is overweight, you need to slide your tandems to redistribute weight before proceeding. After weighing, check the printout for steer, drive, and tandem weights individually. If the drive axles are heavy, slide your trailer tandems forward. If trailer tandems are heavy, slide them rearward. Get a reweigh after adjusting to confirm you are legal on all axles.
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