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Truck Axle Weight Calculator

Free truck axle weight calculator covering all 48 US states. Run any axle layout against state-specific axle weight limits, gross vehicle weight caps, the Federal Bridge Formula, and the lowest permit class that clears your load. Built for owner-operators, dispatchers, and permit specialists who need real answers fast.

Configuration

Truck Configuration

5 axlesTotal: 72,000 lb
TANDEM 4.33 ft · 30.0kTANDEM 4.33 ft · 30.0k2112.0kSTEER4215.0k4315.0k4415.0k4515.0k19.0 ft4.3 ft42.0 ft4.3 ft🔒Wheelbase: 69.7 ft · 5 axles · drag any non-steer wheel to reposition
Axles
1steer
2
3
4
5
Spacing
= 228 in
= 52 in
🔒 locked — click button to unlock
= 52 in
# Tires
Tire width (in)
Axle Weight (lbs)
Role
drive / trailer
drive / trailer
drive / trailer
drive / trailer

Axle Group Thresholds

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Compliance Result

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Axle weight limits, the Federal Bridge Formula, and your truck

Federal axle weight limits cap a single axle at 20,000 lbs, a tandem axle group at 34,000 lbs, and gross vehicle weight at 80,000 lbs on the interstate. Most states follow these legal limits but stack their own rules on top: tridem caps, spacing-scaled tandem limits, tiered annual permits, axle-count-conditional GVW caps, group-balance requirements, and outer-bridge minimums. Every consecutive axle subgroup also has to clear the Federal Bridge Formula, which limits how much weight can sit over a short wheelbase.

This calculator runs the full check at once. Enter axle weights, spacings, and tire widths. Pick a state, road class (interstate or non-interstate), and permit class. The tool evaluates per-axle single-axle limits, steer-axle caps, tandem axle weight limits, tridem and quad group caps, the Federal Bridge Formula on every consecutive subgroup, tire-factor checks by inch or wheel-load, and gross vehicle weight. Every result updates in real time as you edit the truck.

Permit-specific rules are encoded too. Idaho color permits with scaled K-constants, New York Type 24C group-balance, Florida FDOT outer-bridge minimums, Maine's 6-axle grandfather, Oklahoma OL-1 per-position config groups, Vermont's lookup table, and Ohio's spacing-scaled tandem all apply when the relevant permit is selected.

Results show the full check ladder so you can see which constraint binds and by how much. The permit ladder tells you at a glance whether legal clears the load, or which annual or single-trip permit you need. Use this tool to confirm legal compliance before a haul, plan permit-class selection for an oversize or overweight move, or compare per-state axle weight limits across a multi-state route.

Frequently asked questions

What is gross vehicle weight (GVW)?
Gross vehicle weight is the total weight of a fully loaded truck, including the vehicle itself, the trailer, fuel, driver, and cargo. Federal law caps GVW at 80,000 lbs on the interstate without a permit. Most states match this limit on interstate highways but enforce different caps on non-interstate roads. Permits raise the cap for specific routes when the load and axle configuration qualify.
What is gross axle weight rating (GAWR)?
GAWR is the maximum weight a single axle can carry, set by the truck or trailer manufacturer and stamped on the federal certification label inside the driver-side door jamb. GAWR is a structural limit (what the equipment is rated to handle), separate from the legal axle weight limit set by federal and state law. A load must clear both: whichever number is lower applies.
What is the Federal Bridge Formula?
The Federal Bridge Formula is W = 500 × ((L × N) / (N − 1) + 12N + 36). W is the maximum allowed group weight, in pounds. L is the wheelbase of the axle group (first axle to last axle, measured in feet). N is how many axles the group contains. The formula caps how much weight can sit over a short wheelbase, which is what damages bridges. Every consecutive subgroup of axles on the truck has to clear the formula independently, not just the outermost group. A handful of states use a scaled K-constant or a published lookup table for permitted loads, but for legal interstate travel the federal version governs.
What is the federal axle weight limit?
Federal limits cap a single axle at 20,000 lbs and a tandem axle group (two axles spaced 40 to 96 inches apart) at 34,000 lbs on the interstate. Tridem (three-axle) and larger groups are governed by the Federal Bridge Formula plus any state-specific group cap. Most states publish their own per-axle and group limits that match or sit close to federal numbers, with separate non-interstate rules. Steer-axle limits are usually 12,000 to 20,000 lbs depending on tire size and state.
What is a tandem axle?
A tandem axle is a pair of axles spaced 40 to 96 inches apart, treated as a single group for weight-limit purposes. The federal cap for a tandem axle group is 34,000 lbs. Tandems are standard on tractor drive units and on most trailers. Some states (Ohio non-interstate, for example) reduce the tandem cap when the spacing falls below 4 feet, scaling the limit linearly with span.
What is a tridem axle?
A tridem is a group of three consecutive axles, typically used to spread heavier loads across more contact points. Federal law does not set a flat tridem cap; weight is governed by the Federal Bridge Formula plus any state-specific tridem rule. Most states publish caps in the 42,000 to 60,000 lb range depending on spacing. Tridems are common on heavy-haul trailers, lowboys, and dump trucks operating under permit.
What permits do I need for an overweight or oversize load?
It depends on which limit you exceed. Overweight loads (over 80,000 GVW or over the per-axle/group caps) require an overweight permit from each state on the route. Oversize loads (wider than 8’6”, taller than 13’6”, longer than the state’s legal maximum, or with overhangs) require an oversize permit. Many states issue both as a single OS/OW permit. Annual permits cover repeat moves; single-trip permits cover specific origin-destination routes. The permit ladder in this calculator shows which permit class clears your specific load.
How do I calculate axle weight on a truck?
Axle weight is determined by where the load sits over the wheels and how the truck distributes weight to each axle group. The simplest field method is to weigh the truck on a CAT scale or DOT scale: each pad reads one axle group. If you do not have access to a scale, use the manufacturer’s GAWR plus your bill of lading and load placement to estimate. This calculator runs the inverse: given an axle layout and weights, it tells you whether the resulting per-axle and group weights clear federal limits, the state rule book, and the Federal Bridge Formula on every consecutive subgroup.