Axle weight calculator
Enter the steer, drive and trailer weights from your scale ticket and choose single, tandem or spread axles. The calculator checks each group and the gross against the federal Interstate limits, shows how many pounds you have to spare or are over, and points to the group to fix first.
By RonaldUpdated October 2026
How the calculator works
A truck scale ticket breaks your weight into groups: the steer axle, the drive axles and the trailer axles. The calculator checks each one against its federal limit for the Interstate System:
- Single axle: 20,000 lb.
- Tandem (two axles more than 40 inches and no more than 96 inches apart): 34,000 lb.
- Spread pair (two axles more than 96 inches apart): each counts as a single, and the pair is capped by the Bridge Formula at its spacing. At 10 feet that works out to 40,000 lb.
- Gross: 80,000 lb.
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
For each group it shows the weight, the limit and the pounds to spare or over. The bars under the result show each group as a share of its limit, so you can see at a glance which one is tight. The steer limit shown is the federal single-axle figure; your steer axle may also be limited by its manufacturer rating, so check the door label.
Worked example
- Steer
- 11,800 lb
- Drives (tandem)
- 33,600 lb
- Trailer (tandem)
- 33,900 lb
- Gross
- 79,300 lb
- Tightest group
- Trailer, 100 lb spare
- Verdict
- Legal
This ticket is legal, but the trailer tandem has only 100 lb to spare and the drives 400 lb. A slightly heavier load, a different fuel level or a pallet in the wrong place would tip one of them over. Switch the trailer to a spread pair at 10 feet and the trailer group gets 6,100 lb of room, which is why spread-axle flatbeds and step decks are popular for heavy, concentrated freight.
Reading a scale ticket
Most certified truck scales have separate platforms for the steer, drives and trailer, and print each weight on the ticket with the gross. Pull on with all axle groups on their platforms, stay still until the reading settles, and keep the ticket with the load paperwork. Some scales offer a reweigh at a reduced price after you adjust, which is the moment to use this calculator: put in the first ticket, decide which way to slide, then reweigh. Write the final ticket numbers on the load paperwork too: if you're stopped later, a ticket from the shipper's area showing every group legal is the best record you can have.
If you're weighing a hotshot or a box truck, the same idea applies with fewer groups. A box truck is a steer axle and a single or tandem drive with no trailer. A hotshot is usually a single steer, a single drive and a tandem gooseneck trailer.
What to do when a group is over
If the gross is legal but one group is over, the fix is shifting weight, not removing it:
- Drives over, trailer has room: slide the trailer tandems forward.
- Trailer over, drives have room: slide the trailer tandems back.
- Steer heavy, drives have room: slide the fifth wheel back.
- Drives heavy, steer has room: slide the fifth wheel forward.
Our tandem slide and fifth wheel weight shift calculator estimates how far to move. If the gross is over, the load has to change, or, for a nondivisible load, you need a permit from each state on the route.
On an open deck, how the freight sits on the trailer decides most of this before you ever reach the scale. Heavy pieces belong over the axles, not at the ends. Our guide to flatbed dimensions and weight capacity covers deck loading, and the federal legal truck size limits chart lists the other limits. For a full Bridge Formula check on every axle group, use the truck weight limit checker.
Calculator questions
Note 01What are the legal axle weights for a semi?
On the Interstate System, a single axle may carry 20,000 lb, a tandem 34,000 lb, and the whole truck 80,000 lb gross, subject to the Bridge Formula. A typical five-axle tractor-trailer has about 12,000 lb on the steer and up to 34,000 lb each on the drives and the trailer tandem.
Note 02Why is my steer axle so heavy?
Usually the fifth wheel is set too far forward, which pushes trailer weight onto the steer and drives. A full fuel load adds weight forward too. Sliding the fifth wheel back moves weight from the steer to the drives; check the drives still have room before you do it.
Note 03How do I fix overweight drives?
Slide the trailer tandems toward the front of the trailer to move weight onto the trailer axles, or slide the fifth wheel forward to move some onto the steer. Each step shifts a few hundred pounds, depending on the trailer and the load. If both groups are full, the load itself is too heavy.
Note 04What is a spread axle?
A pair of trailer axles set more than 96 inches apart, common on flatbeds and step decks. Because they're too far apart to count as a tandem, each counts as a single axle, and together they're limited by the Bridge Formula at their spacing, about 40,000 lb at 10 feet instead of 34,000 lb.
Note 05Do states allow heavier axle weights?
Some do, off the Interstate or under limits grandfathered from before the federal rules, and states issue permits for nondivisible loads. Others post lower limits on certain roads or in spring thaw. The federal numbers are the baseline for the Interstate; check the states on your route for anything else.
Every load matched to your axles before you hook up
We check weight against your setup so the scale is never the surprise.