Trucker Tools
Axle Weight Calculator and DOT Weight Limits per Axle
Federal limits on the Interstate are 20,000 lb on any one axle, 34,000 lb on a tandem and 80,000 lb gross, and every group of axles must also pass the bridge formula (23 CFR 658.17). There is no federal 12,000 lb steer limit. 23 CFR 658.17(f) only stops states from setting a steering-axle cap below 20,000 lb or the axle manufacturer's rating, whichever is lower. Tires also may not be loaded past the load rating on the sidewall (49 CFR 393.75(g)).
Assumptions
- Federal Interstate limits only. State limits, permits and grandfather rights vary; see FHWA's state compilation.
- Each tandem's ticket weight is split evenly between its two axles for the bridge groups. Your scale ticket only shows group totals.
- Bridge groups use L rounded down to the whole foot (FHWA's table is in whole feet; no official fractional-foot rule was found). The result at the exact length is shown too.
- The formula result is rounded to the nearest 500 lb, an exact half rounds down, and it is capped at 80,000.
- The federal single-axle screen stays at 20,000 lb. An entered steer rating is a separate equipment check, not a state legal cap. Tire loads are not calculated from group weights: check each tire against its sidewall load rating (49 CFR 393.75(g)). A passing screen is not a finding that the truck is legal.
- No auxiliary power unit (APU) allowance is added. 23 CFR 658.17(n) covers it; check your state.
The rules
| Rule | Limit | Source |
|---|---|---|
| Gross vehicle weight | 80,000 lb, unless the bridge formula sets a lower number | 23 CFR 658.17(b) |
| Any one axle, including any axle in a group | 20,000 lb | 23 CFR 658.17(c) |
| Tandem axle | 34,000 lb | 23 CFR 658.17(d) |
| Single vs tandem | Axles 40 in or less apart count as one axle; over 40 in and up to 96 in apart are a tandem | FHWA Bridge Formula Weights; 23 CFR 658.5 |
| Any group of 2 or more consecutive axles | Bridge formula W = 500 x (LN/(N-1) + 12N + 36), to the nearest 500 lb | 23 CFR 658.17(e) |
| Two tandems 36 ft or more apart (first to last axle) | 34,000 lb each | 23 CFR 658.17(e) |
| Steering axle | States may not set a limit below 20,000 lb or the axle manufacturer rating, whichever is lower | 23 CFR 658.17(f) |
| Tolerances | Limits include all tolerances; only a portable-scale allowance, never over 5%, is allowed | 23 CFR 658.17(g) |
Worked example (FHWA)
FHWA's own example truck carries 12,000 lb on the steer and 17,000 lb on each of the other four axles: 80,000 gross.
- Axles 1-3: 46,000 lb actual. L = 20 ft, N = 3: W = 500 x (20 x 3 / 2 + 36 + 36) = 51,000. OK.
- Axles 1-5: 80,000 lb actual. L = 51 ft, N = 5: 500 x (63.75 + 60 + 36) = 79,875, which rounds to 80,000. OK.
- Axles 2-5: 68,000 lb actual. L = 35 ft, N = 4: 500 x (46.67 + 48 + 36) = 65,333, which rounds to 65,500. Over by 2,500 lb. Spreading axles 2 to 5 to 36 ft or more would let both tandems carry 34,000 each.
Heavy on the drives or the trailer tandem? The slide helper works out how many holes to move from your own tickets.
FAQ
What is the legal weight per axle?
On the Interstate, federal limits are 20,000 lb on a single axle, 34,000 lb on a tandem and 80,000 lb gross, and every group of axles must also pass the bridge formula (23 CFR 658.17). States can allow different weights off the Interstate and under grandfather rights, so check your state's rules for the roads you run.
What is the steer axle weight limit?
There is no federal 12,000 lb steer limit. Under 23 CFR 658.17(f), states may not set a steering-axle cap below 20,000 lb or the axle manufacturer's rating, whichever is lower. Tires also may not carry more than the load rating marked on the sidewall (49 CFR 393.75(g)). Read both the axle tag and the tire.
What is the legal weight for a 53 ft trailer per axle?
Federally, the trailer tandem can carry up to 34,000 lb, each axle in it no more than 20,000 lb, and the whole truck 80,000 lb. The bridge formula can lower those numbers depending on axle spacing, and state limits off the Interstate can differ, so check the spacing as well as the weight (23 CFR 658.17).
What counts as a tandem axle?
A tandem is two or more consecutive axles whose centers are more than 40 inches and not more than 96 inches apart, and it is limited to 34,000 lb. Axles 40 inches or less apart count as one single axle at 20,000 lb. Axles more than 96 inches apart are checked with the bridge formula (FHWA; 23 CFR 658.5).
Can the drives and trailer tandem both carry 34,000 lb?
Yes, if the first axle of the drive tandem and the last axle of the trailer tandem are 36 feet or more apart. That exception in 23 CFR 658.17(e) lets two consecutive tandems carry 34,000 lb each even though the bridge formula alone would allow about 66,000 lb at 36 feet. The gross still cannot exceed 80,000.
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Sources
- 23 CFR 658.17, Weight (eCFR)
- 23 CFR 658.5, Definitions (eCFR)
- FHWA, Bridge Formula Weights (FHWA-HOP-19-028)
- FHWA, state truck size and weight laws (Appendix B)
- 49 CFR 393.75, Tires (eCFR)
Disclaimer: For general information. Federal limits from 23 CFR 658 and 49 CFR; state limits, permits and enforcement vary. Check your state's CDL manual and DOT before you rely on a number. Not legal or tax advice.
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