How much load is on each axle? Axle load calculator for trucks and semi-trailers

What it calculates

The calculator has two modes. Rigid truck: from the wheelbase, the tare on the front axle and on the rear axle or axle group, the weight of the load and how far its centre sits behind the front axle, it works out the weight on the front axle and on the rear axle, or on a tandem or tridem rear group and on each of its axles. Tractor and semi-trailer: from the tractor’s wheelbase, the position of the fifth wheel, the tare of both vehicles, the distance from the kingpin to the semi-trailer’s axles and where the load sits, it works out the load on the kingpin, on the front axle, on the drive axle or group and on the semi-trailer’s axle or group. Every axle and group is checked against the chosen country’s limit; the result shows any excess and links the provision behind the limit with its source.

Formula

Rigid truck

The axles share the load like a lever:

• Rear axle or group = tare on the rear axle or group + load × x ÷ wheelbase
• Front axle = tare on the front axle + load − load × x ÷ wheelbase
• x: distance of the load’s centre of gravity behind the front axle (m). With a tandem or tridem the wheelbase runs to the centre of the group.
• Each axle of a group = group load ÷ number of axles.

Tractor and semi-trailer

The semi-trailer is a lever between the kingpin and its axles; the kingpin load then rests on the tractor’s fifth wheel, a second lever:

• Kingpin = semi-trailer tare on the kingpin + load × (a − x) ÷ a
• Semi-trailer axle or group = semi-trailer tare on its axles + load × x ÷ a
• Drive axle or group = tractor tare on it + kingpin load × (wheelbase − f) ÷ wheelbase
• Front axle = tractor tare on the front axle + kingpin load × f ÷ wheelbase
• a: kingpin to the centre of the semi-trailer’s axle or group (m); x: distance of the load’s centre behind the kingpin (m); f: how far the fifth wheel sits ahead of the drive axle or group centre (m). The wheelbase runs from the front axle to the drive axle or group centre.

Single-axle limits

• Turkey: KTY Art. 128, 10 tonnes on a single non-driving axle and 11.5 tonnes on a single driving axle. The calculator treats the front axle and a semi-trailer’s single axle as non-driving, and the rear axle of a truck or tractor as driving.
• EU: Directive 96/53/EC, 10 and 11.5 tonnes; the same figures in Germany, Austria, Switzerland, Poland, the UK and Ireland. Spain allows 12 tonnes on a single driving axle; Italy 12 tonnes on any axle.
• Russia: Decree No. 2060. The limit depends on the road’s axle-load class and on the tyres: on a 10-tonne road 9 tonnes on a single-tyred axle and 10 on a twin-tyred one; on an 11.5-tonne road 10.5 and 11.5 tonnes. These are permit thresholds.
• Eurasian Economic Union and Kazakhstan: 10.5 tonnes on a single-tyred axle and 11.5 on a twin-tyred one (roads of the Eurasian transport corridors).
• United States: 23 CFR 658.17(c), 20,000 lb on any single axle (9,072 kg with NIST’s pound).
• Mexico: NOM-012-SCT-2-2017, Tabla A-2, by road type. On an ET/A road 6.5 tonnes on a single axle with two tyres and 12.5 tonnes on a single driving axle with four tyres; a semi-trailer’s single axle counts as a non-driving axle with four tyres, 11 tonnes.

Tandem and tridem limits

A group’s limit is picked by the spacing between its axles, by whether the group belongs to a motor vehicle (the rear group of a truck, the drive group of a tractor) or to a semi-trailer, and in Russia, the EAEU and Kazakhstan by road class and tyres. A limit the law writes for any vehicle is used for both. The tridem choice is offered only where the data has a tri-axle limit for that kind of vehicle. Where no bracket covers the spacing, the result shows the load with “no limit for this group in the data” and puts no figure in its place.

• EU, Directive 96/53/EC, Annex I:
  • tandem axles of trailers and semi-trailers (3.2): 11 tonnes below 1.0 m, 16 tonnes from 1.0 m to below 1.3 m, 18 tonnes from 1.3 m to below 1.8 m and 20 tonnes from 1.8 m;
  • tri-axles of trailers and semi-trailers (3.3): 21 tonnes up to 1.3 m and 24 tonnes over 1.3 m up to 1.4 m;
  • tandem axles of motor vehicles (3.5): 11.5 tonnes below 1.0 m, 16 tonnes from 1.0 m to below 1.3 m and 18 tonnes from 1.3 m to below 1.8 m, or 19 tonnes in that last bracket under conditions.
• Turkey and Germany: the EU brackets; their tri-axle limits (21 and 24 tonnes) are written for any vehicle, so they hold for a truck’s tridem as well.
• Austria: the EU brackets; KFG 1967 § 4 (8) writes the tri-axle limits for trailers and semi-trailers only.
• Switzerland: VRV Art. 67, the EU brackets for tandems, and tri-axles of any vehicle: 21 tonnes up to 1.3 m, 24 tonnes over 1.3 m up to 1.4 m and 27 tonnes over 1.4 m.
• Poland: Dz.U. 2024 poz. 502, § 5 ust. 1: the EU brackets, except that a motor vehicle’s tandem keeps 18 or 19 tonnes up to and including 1.8 m; tri-axles of motor vehicles and trailers alike: 21 and 24 tonnes, and 27 tonnes over 1.4 m up to 1.8 m. Beside these the calculator shows two higher figures, each with its condition:
  • pkt 8a, a motor vehicle’s tri-axle “w której co najmniej dwie osie składowe są osiami napędowymi” (in which at least two of the axles are driven): 24 tonnes up to 1.3 m and 27 tonnes over 1.3 m up to 1.8 m. The limit shown first stays that of a tri-axle with one driven axle (pkt 8).
  • § 4 ust. 2: for “pojazdów zarejestrowanych po raz pierwszy przed dniem 13 marca 2003 r.”, vehicles first registered before 13 March 2003, the axles of a group may be up to 2.00 m apart instead of 1.80 m. Over 1.8 m up to 2.0 m a motor vehicle’s tandem then keeps 18 tonnes, or 19 tonnes under conditions (pkt 6 c and 7 c), and a tri-axle 27 tonnes (pkt 3 c and 8 c); pkt 8a has no such extension. For later vehicles the calculator shows no limit there.
• Spain: RGV Annex IX: 12 tonnes for a motor vehicle’s tandem below 1.0 m, and tri-axles of trailers and semi-trailers 21 tonnes up to 1.3 m and 27 tonnes over 1.3 m up to 1.4 m; otherwise the EU figures.
• United Kingdom: AW Regulations 1998, Schedule 3: a driving tandem 18 tonnes, or 19 tonnes with twin tyres and road friendly suspension or with twin tyres and no axle over 9,500 kg; below 1.3 m Table 6 lowers it to 11.5 tonnes (below 1 m) and 16 tonnes. A non-driving tandem 20 tonnes, lowered below 1.8 m to 11, 16 and 18 tonnes; a tri-axle 24 tonnes, 21 tonnes up to 1.3 m.
• Ireland: a tandem 11.5, 16 and 18 tonnes by the same brackets, 19 tonnes for a motor vehicle’s under conditions and 20 tonnes for a trailer’s from 1.8 m; a tri-axle 21 tonnes below 1.3 m and 24 tonnes from 1.3 m.
• Italy: CdS art. 62, for any vehicle: 12 tonnes below 1.0 m, 16 tonnes from 1.0 m to below 1.3 m and 20 tonnes from 1.3 m to below 2.0 m; the data has no tri-axle limit.
• Russia: Decree No. 2060, by road class and by spacing: up to 1.0 m, over 1.0 to 1.3 m, over 1.3 to 1.8 m and over 1.8 to 2.5 m. With twin tyres a tandem may carry 11, 14, 16 and 18 tonnes on a 10-tonne road and 12.5, 16, 18 and 20 tonnes on an 11.5-tonne road; a tri-axle 16.5, 19.5, 22.5 and 23 tonnes, and 18, 21, 24 and 26 tonnes.
• Eurasian Economic Union and Kazakhstan: with twin tyres a tandem 12.5, 16, 18 and 20 tonnes and a tri-axle 18, 21, 24 and 26 tonnes, by the same spacings.
• Mexico: Tabla A-2 sets group limits by tyres, not by spacing. On an ET/A road 21 tonnes for a driving tandem with eight tyres, 19 tonnes for a non-driving tandem with eight tyres and 26.5 tonnes for a tri-axle with twelve tyres; for a type D road the table has no tri-axle figure.
• United States: the bridge formula below.

Three points of the directive, in its own words

• No tri-axle limit for motor vehicles. Point 3.3 is headed “Tri-axles of trailers and semi-trailers”, and no point of Annex I 3 sets a tri-axle limit for a motor vehicle. For an EU rigid truck the tridem choice is not offered.
• No motor-vehicle tandem limit from 1.8 m. Point 3.5, “Tandem axles of motor vehicles”, ends with the bracket “1,3 m or greater but less than 1,8 m”; for trailers, point 3.2.4 goes on to “1,8 m or more” with 20 tonnes. Annex I gives no tandem limit for a motor vehicle whose axles are 1.8 m or more apart, and the calculator shows no limit there.
• 19 tonnes only under conditions. Point 3.5.3 allows 19 tonnes instead of 18 “where the driving axle is fitted with twin tyres and air suspension or suspension recognized as being equivalent within the Community as defined in Annex II, or where each driving axle is fitted with twin tyres and where the maximum weight for each axle does not exceed 9,5 tonnes”. The calculator shows both figures; which one applies depends on the vehicle.

United States: the bridge formula

23 CFR 658.17 sets three caps on the Interstate System: “The maximum gross weight upon any one axle, including any one axle of a group of axles, or a vehicle is 20,000 pounds” (c); “The maximum gross weight on tandem axles is 34,000 pounds” (d); and 80,000 lb gross (b). Paragraph (e) adds that no vehicle may be moved “when the gross weight on two or more consecutive axles exceeds the limitations prescribed by the following formula, referred to as the Bridge Gross Weight Formula”:

• W = 500 × (L × N ÷ (N − 1) + 12 × N + 36)
• W: “overall gross weight on any group of two or more consecutive axles to the nearest five hundred pounds” (23 U.S.C. 127(a)(2)); L: distance in feet between the outer axles of the group; N: number of axles in the group.

A tandem with its axles 4 ft apart gives 500 × (4 × 2 ÷ 1 + 24 + 36) = 34,000 lb, the tandem cap; five axles spread over 51 ft give 500 × (63.75 + 60 + 36) = 79,875 lb, which rounds to 80,000 lb. Paragraph (e) goes on: “except that two consecutive sets of tandem axles may carry a gross load of 34,000 pounds each if the overall distance between the first and last axle is 36 feet or more. In no case shall the total gross weight of a vehicle exceed 80,000 pounds.”

For the US the calculator shows the formula’s result next to the 20,000 lb single-axle and 34,000 lb tandem caps for each group (for a tridem the formula alone); for the whole vehicle the 80,000 lb cap and the formula over all its axles; and for a tractor with a drive tandem and a semi-trailer tandem the formula over those four axles, or 2 × 34,000 lb when they span 36 ft or more. Metres become feet at 0.3048 m to the foot.

Examples

Rigid truck. A truck with a 4.5 m wheelbase carries 4,500 kg of tare on the front axle and 2,500 kg on the rear; the centre of a 9,000 kg load sits 3 m behind the front axle. The rear axle carries 2,500 + 9,000 × 3 ÷ 4.5 = 8,500 kg and the front axle 4,500 + 9,000 − 6,000 = 7,500 kg; 16,000 kg in total. Both axles are within Turkey’s 10- and 11.5-tonne limits, and the total is below the 18 tonnes KTY Art. 128 sets for a two-axle motor vehicle. The calculator opens on this example.

Tractor and semi-trailer. A tractor with a 3.6 m wheelbase has its fifth wheel 0.45 m ahead of the drive axle, and 5,000 kg of tare on the front axle and 2,500 kg on the drive axle. The centre of the semi-trailer’s tri-axle, its axles 1.31 m apart, is 8 m behind the kingpin; the semi-trailer’s tare is 2,000 kg on the kingpin and 4,500 kg on the axles, and the centre of a 24,000 kg load sits 6 m behind the kingpin. The kingpin carries 2,000 + 24,000 × (8 − 6) ÷ 8 = 8,000 kg and the tri-axle 4,500 + 24,000 × 6 ÷ 8 = 22,500 kg, 7,500 kg per axle. On the tractor the drive axle carries 2,500 + 8,000 × (3.6 − 0.45) ÷ 3.6 = 9,500 kg and the front axle 5,000 + 8,000 × 0.45 ÷ 3.6 = 6,000 kg; 38,000 kg in all. Under Directive 96/53/EC a tri-axle with its axles over 1.3 m and up to 1.4 m apart may carry 24 tonnes (Annex I 3.3.2) and the drive axle 11.5 tonnes. The tractor and semi-trailer mode opens on this example.

Assumptions and limits

• Within a tandem or tridem the load is shared equally between the axles; on a real vehicle the suspension and the spacing decide the split, so one axle of a group may carry more.
• One spacing is used between all the axles of a group, and the group’s centre is the middle of its outer axles.
• The load counts as if it were concentrated at its centre of gravity.
• How the tare splits between the axles and the kingpin is the user’s input.
• Where the limit depends on the tyres (Russia, the EAEU, Kazakhstan, Mexico), single tyres are taken on the front axle and twin tyres on every other axle.
• For the US the bridge formula is applied to each group, to the whole vehicle and to the two tandems of a tractor and semi-trailer; other runs of consecutive axles, such as the front axle with the drive group, are not checked.
• A truck with a drawbar trailer, the gross weight limits and the drive axle’s minimum share of the total weight are not worked out here.
• Some limits carry conditions (in Ireland, for example, 11.5 tonnes on a driving axle needs twin tyres and air suspension); the linked provision sets them out.
• The tyres limit the load as well; the tyre load index calculator gives what the tyres of an axle can carry.

Source notes

The axle and group limits come from each country’s legislation, with the provision (listed under Sources); the provision and source of each limit shown are linked under the result. The directive is quoted from its consolidated text on EUR-Lex, the US rules from 23 CFR 658.17 on eCFR and from 23 U.S.C. 127 on govinfo. US figures in pounds are converted with NIST’s pound. For gross weight limits there is the payload calculator, and for axle layouts the site’s article on axle configurations.