Idaho Truck Weight and Size Limits
Legal limits for a truck in Idaho without a permit: Interstate axle and gross weights, height, width, and semitrailer length, each with its official source.
Idaho limits at a glance
| Limit | Idaho | Source |
|---|---|---|
| Interstate gross weight | 80,000 lb | 23 CFR 658.17, Weight (eCFR) |
| Interstate single axle | 20,000 lb | 23 CFR 658.17, Weight (eCFR) |
| Interstate tandem axle | 34,000 lb | 23 CFR 658.17, Weight (eCFR) |
| Width (National Network) | 102 in | 23 CFR 658.15, Width (eCFR) |
| Height | 14 ft | Idaho Code § 49-1010(2) |
| Semitrailer length | 48 ft; 53 ft on National Network routes, access routes within one road mile of them, and approved state highways | Idaho Code § 49-1010(3)(b) |
| Grandfathered semitrailer length | 48 ft | 23 CFR part 658, Appendix B, Grandfathered Semitrailer Lengths (eCFR) |
Interstate weight limits
Federal law sets the Interstate limits at 20,000 lb on a single axle, 34,000 lb on a tandem, and 80,000 lb gross, with the bridge formula on every axle group (23 CFR 658.17). States may keep higher limits they had before the federal limits took effect ("grandfather rights").
Grandfathered: up to 105,500 lb GVW on all National Network routes.
FHWA on Idaho: Idaho has a grandfather provision under Federal law (23 CFR Part 658, Appendix C) to allow vehicles to operate up to 105,500 lbs. GVW on all NN routes in the State, which includes the Interstate system. See the Routes section for a full description of the routes to which this grandfather provision applies.
Bridge formula check with Idaho limits
A 5-axle tractor-trailer is filled in. Change the spacings and weights to match your rig; the limits for single axles, tandems, and gross are Idaho's Interstate limits.
Your result
Idaho limits off the Interstate
FHWA's summary of Idaho law for trucks in regular operation (no permit), including non-Interstate highways. It reflects state law as of October 1, 2012; check the state for later changes.
- Single axle
- 20,000 lbs.
- Tandem axle
- 34,000 lbs.
- Tridem axle
- Per State weight table
- Gross weight
- 80,000 lbs.
- Other
- 10,000 lbs. per wheel
Where Idaho allows more than federal limits
- Idaho allows a maximum of 37,800 lbs. for tandem axles when gross weight does not exceed 79,000 lbs. GVW on the Interstate with certain exempt commodities.
- Vehicles hauling agricultural products are allowed an additional 2,000-pound tolerance on any axle, bridge, or GVW limit on non-Interstate highways.
- Authorities with jurisdiction are authorized to designate special routes on highways that allow vehicles carrying logs, poles, piling, and mining material at weights in excess of State limits.
Height, width, and length
- Width: 102 inches. States may not set a width limit of more or less than 102 inches on the National Network (23 CFR 658.15(a)). Permits can allow wider loads.
- Height: 14 ft. There is no federal height limit; each state sets its own.
- Semitrailer length: 48 ft; 53 ft on National Network routes, access routes within one road mile of them, and approved state highways
- Grandfathered semitrailer length: 48 ft. The minimum semitrailer length the state must allow in a tractor-semitrailer combination on the National Network, based on lengths legal in the state on December 1, 1982. Federal law also requires at least 48 ft (23 CFR 658.13(b)(1)).
Over these limits you need a permit. Idaho oversize/overweight permits (800-662-7133).
Idaho compared with neighboring states
| State | Gross | Single | Tandem | Height | Semitrailer |
|---|---|---|---|---|---|
| Idaho | 80,000 lb | 20,000 lb | 34,000 lb | 14 ft | 48 ft |
| Montana | 80,000 lb | 20,000 lb | 34,000 lb | 14 ft | 53 ft |
| Nevada | 80,000 lb | 20,000 lb | 34,000 lb | 14 ft | Pending |
| Oregon | 80,000 lb | 20,000 lb | 34,000 lb | 14 ft | Pending |
| Utah | 80,000 lb | 20,000 lb | 34,000 lb | 14 ft | 53 ft |
| Washington | 80,000 lb | 20,000 lb | 34,000 lb | 14 ft | 53 ft |
Sources
Source: 23 CFR 658.17, Weight (eCFR) · Last verified Sep 28, 2026
Source: FHWA, Compilation of Existing State Truck Size and Weight Limit Laws (Report to Congress, May 2015), Appendix A: Idaho · Effective Oct 1, 2012 · Last verified Sep 28, 2026
Source: FHWA, Compilation of Existing State Truck Size and Weight Limit Laws (Report to Congress, May 2015), Appendix B: Summary of State Exceptions to Federal Truck Weight Limits · Effective Oct 1, 2012 · Last verified Sep 28, 2026
Source: 23 CFR 658.15, Width (eCFR) · Last verified Sep 28, 2026
Source: 23 CFR part 658, Appendix B, Grandfathered Semitrailer Lengths (eCFR) · Last verified Sep 28, 2026
Source: Idaho Code § 49-1010(3)(b) · Last verified Sep 28, 2026
Source: FHWA, Oversize/Overweight Load Permits: State permit contacts · Last verified Sep 28, 2026
Limits change, and cities, counties, and posted bridges can set lower ones. Check with Idaho before you run a load near the limits. Page data last verified Sep 28, 2026.