Truck weight limit checker
Enter the weight on each axle and the distances between them. The checker tests every axle against the 20,000 lb single and 34,000 lb tandem limits, the 80,000 lb gross limit, and every axle group against the federal Bridge Formula, then shows the tightest group.
By RonaldUpdated October 2026
How the checker works
The checker applies the federal weight rules for the Interstate System, written in 23 CFR 658.17. It runs three kinds of checks.
Axle limits. Any single axle may carry up to 20,000 lb. A tandem, meaning two or more consecutive axles more than 40 inches and no more than 96 inches apart, may carry up to 34,000 lb. The checker groups your axles into tandems using that spacing rule.
Gross limit. The whole vehicle may weigh up to 80,000 lb.
Bridge Formula. Every group of two or more consecutive axles is checked against W = 500 × (LN / (N − 1) + 12N + 36), where L is the distance in feet between the outer axles of the group and N is the number of axles. FHWA defines W to the nearest 500 lb; when a result lands exactly on a half, the checker rounds down, the cautious choice. One exception applies: two consecutive tandems may carry 34,000 lb each when the first and last axles are 36 feet or more apart.
Source:23 CFR 658.17, Interstate weight limits: 80,000 lb gross, 20,000 single, 34,000 tandem, Bridge Formula, grandfather rights, permits (2025 edition) · checked 2026-1023 CFR 658.5, definitions: tandem axle = consecutive axles more than 40 in and not more than 96 in apart (2025 edition) · checked 2026-10FHWA, Federal Bridge Formula B: W is the maximum weight on a group of two or more axles, to the nearest 500 pounds · checked 2026-10
The box drawn under the result marks the tightest axle group: the one with the least room left under its limit. That's the group to fix first if you're over.
Worked example
- Axle weights
- 12k / 17k / 17k / 17k / 17k
- Axle 1 to 5
- 58.4 ft
- Gross
- 80,000 lb
- Drive tandem
- 34,000 / 34,000
- Trailer tandem
- 34,000 / 34,000
- Whole truck, bridge
- 80,000 / 80,000
This truck is right at every limit at once, which is legal but leaves no room. Shorten the gap between the drives and the trailer tandem to 20 feet and the four rear axles carry 68,000 lb against a bridge limit of 61,000 lb, a fail even though no single axle is over. That's why a short wheelbase or a tandem slid all the way forward can make a legal-looking load illegal.
Getting accurate axle weights
The checker is only as good as the numbers you put in. A certified truck scale with separate platforms gives you the steer axle, the drive tandem and the trailer tandem in one pass. Weigh loaded, with a full tank if that's how you'll run, because fuel moves weight onto the steer and drive axles. Measure axle spacing center to center with a tape, or take it from the truck and trailer specification sheets. On the open deck, how the freight sits on the trailer moves weight from one tandem to the other.
What good and bad results mean
A pass means the configuration meets the federal limits on the Interstate. It doesn't cover state limits on other roads, special local restrictions, posted bridges or seasonal frost laws, and it assumes your weights are accurate. Scale your truck when you're close.
A fail tells you which rule broke. Axle over: move weight off that axle. Tandem over: slide the fifth wheel or the trailer tandems. Bridge group over: the axles are too close for the weight, so spread them out or carry less. Gross over: the load is too heavy for a legal move without a permit.
States, permits and grandfathered limits
The federal rules set what states must allow on the Interstate. States can still issue permits for nondivisible loads above those limits, and some keep higher weights that were legal under their laws before the federal limits applied. Off the Interstate, each state sets its own limits. Before you route a heavy load, check every state on the way. For the trailer side, see our flatbed dimensions and weight capacity guide and the federal legal truck size limits chart.
To split weight across axles in more detail, use the axle weight calculator. Running mountain routes in winter? Check the chain law checker by state.
Calculator questions
Note 01What is the legal weight limit for a semi truck?
On the Interstate System the federal limits are 80,000 lb gross, 20,000 lb on a single axle and 34,000 lb on a tandem, plus the Bridge Formula for every group of axles. A typical five-axle tractor-trailer needs about 51 feet between its first and last axles to reach 80,000 lb under the formula.
Note 02What is the Bridge Formula?
It limits the weight on any group of two or more consecutive axles based on how many axles there are and how far apart the outer ones sit: W = 500 times (LN divided by N minus 1, plus 12N, plus 36), rounded to the nearest 500 lb. Spreading weight over a longer distance lets you carry more without overloading bridges.
Note 03Do states have different weight limits?
Yes. Federal limits apply on the Interstate and reasonable access to it. Off the Interstate, states set their own limits, and some keep higher limits grandfathered from before the federal rules. A route that leaves the Interstate can face lower or higher limits, so check each state's rules for the roads you'll use.
Note 04What if my load is too heavy?
If the load can be split, it must be: overweight permits are for nondivisible loads, like a single large machine. Otherwise shift weight between axles by moving the fifth wheel or sliding the trailer tandems, or carry less. For a nondivisible load, each state on the route issues its own overweight permit.
Note 05What counts as a tandem axle?
Two or more consecutive axles whose centers sit more than 40 inches and no more than 96 inches apart. Axles farther apart than 96 inches are treated as separate single axles for the axle limits, while the Bridge Formula still applies to them as a group.
Loads that fit your axles, booked before you roll
We check the weight on every load against your truck before it reaches you.