Axle Weight Calculator

Calculate the load on the steer axle, the drive tandem and the trailer tandem of a five-axle tractor-semitrailer from the empty weights of the vehicle and the weight and position of the cargo, and check each against the federal limits on the Interstate System.

Source 23 CFR 658.17Figures verified against the published regulation on November 1, 2026

Tractor, Trailer and Cargo

Tractor, Empty

Steer axle weight lb Drive tandem weight lb From a scale ticket of the tractor alone, fueled and with its driver. Steer axle to drive tandem center in Drive tandem spread in Fifth wheel ahead of drive tandem center in

Cargo

Cargo weight lb Center of the cargo from the front wall in For cargo spread evenly from the front wall, half the length it occupies.

Semitrailer

Empty weight lb Kingpin to trailer tandem center in Trailer tandem spread in Front wall to kingpin in

Within the limits76,000 lb gross · 18 limits checked · Least margin 1,947 lb, Tandem Axle, Trailer Tandem

Axle Loads

Axle Group	Load	Limit	Margin
Steer Axle	12,327 lb	20,000 lb	+7,673
Drive Tandem	31,620 lb	34,000 lb	+2,380
Trailer Tandem	32,053 lb	34,000 lb	+1,947
Gross Combination Weight	76,000 lb	80,000 lb	+4,000

Compliance Checks

18 checked, 0 exceeded

Rule	Applies To	Actual	Limit	Margin	Reference
Tandem AxleAxle spacing 49 in falls in band 40 < d ≤ 96 in (23 CFR 658.5).	Trailer Tandem	32,053 lb	34,000 lb	+1,947	23 CFR 658.17(d)
Bridge Formula	Trailer 1 to Trailer 2 (2 axles, 4 ft)	32,053 lb	34,000 lb	+1,947	23 CFR 658.17(e)
Tandem AxleAxle spacing 54 in falls in band 40 < d ≤ 96 in (23 CFR 658.5).	Drive Tandem	31,620 lb	34,000 lb	+2,380	23 CFR 658.17(d)
Bridge Formula	Drive 1 to Drive 2 (2 axles, 4 ft)	31,620 lb	34,000 lb	+2,380	23 CFR 658.17(e)
Single Axle	Trailer 1	16,026 lb	20,000 lb	+3,974	23 CFR 658.17(c)
Single Axle	Trailer 2	16,026 lb	20,000 lb	+3,974	23 CFR 658.17(c)
Gross Vehicle Weight	Whole vehicle	76,000 lb	80,000 lb	+4,000	23 CFR 658.17(b)
Bridge Formula	Steer to Trailer 2 (5 axles, 53 ft)	76,000 lb	80,000 lb	+4,000	23 CFR 658.17(e)
Single Axle	Drive 1	15,810 lb	20,000 lb	+4,190	23 CFR 658.17(c)
Single Axle	Drive 2	15,810 lb	20,000 lb	+4,190	23 CFR 658.17(c)
Bridge Formula	Steer to Drive 2 (3 axles, 17 ft)	43,947 lb	48,500 lb	+4,553	23 CFR 658.17(e)
Bridge Formula	Drive 1 to Trailer 2 (4 axles, 41 ft)	63,673 lb	69,500 lb	+5,827	23 CFR 658.17(e)
Single Axle	Steer	12,327 lb	20,000 lb	+7,673	23 CFR 658.17(c)
Bridge Formula	Steer to Drive 1 (2 axles, 12 ft)	28,137 lb	42,000 lb	+13,863	23 CFR 658.17(e)
Bridge Formula	Steer to Trailer 1 (4 axles, 49 ft)	59,974 lb	74,500 lb	+14,526	23 CFR 658.17(e)
Bridge Formula	Drive 2 to Trailer 2 (3 axles, 36 ft)	47,863 lb	63,000 lb	+15,137	23 CFR 658.17(e)
Bridge Formula	Drive 1 to Trailer 1 (3 axles, 37 ft)	47,647 lb	63,500 lb	+15,853	23 CFR 658.17(e)
Bridge Formula	Drive 2 to Trailer 1 (2 axles, 32 ft)	31,837 lb	62,000 lb	+30,163	23 CFR 658.17(e)

How the axle weights are calculated

The semitrailer rests on the kingpin at the front and on its tandem at the rear. Taking moments about the center of the trailer tandem gives the weight carried by the kingpin, and the remainder of the weight of the trailer and its cargo is carried by the trailer tandem. The tractor rests on its steer axle and its drive tandem, and carries its own weight together with the weight on the kingpin. Taking moments about the center of the drive tandem gives the steer axle weight, and the remainder is carried by the drive tandem.

Cargo placed further forward therefore adds weight to the steer axle and the drive tandem, and cargo placed further back adds weight to the trailer tandem. The weight within a tandem is divided equally between its axles.

Adjusting the axle weights

Sliding the trailer tandem rearward moves weight from the trailer tandem to the kingpin, and so to the drive tandem. Sliding the fifth wheel forward moves weight from the drive tandem to the steer axle. Moving the cargo has the greatest effect, and the load planner positions the cargo and the trailer tandem so that every limit is met.

Assumptions

The calculator treats the vehicle as standing on level ground. The empty weight of the semitrailer is taken to act at the point it acts on the planner's 53 ft van, and the cargo as a single weight at its center. The empty weights of the tractor are best taken from a scale ticket of the tractor alone, with fuel and driver. The weights recorded on a certified scale are authoritative.