A factory tandem-axle dump body is typically 14 to 16 ft long inside, 96 in (8 ft) wide, and 48 in tall at the sides, producing 10 to 16 cu yd of struck capacity; tandem chassis in 10-wheeler configuration are legal for 12 to 16 tons of gravel or asphalt under typical GVWR envelopes [S2][S4].
Tonnage, not yardage, is the binding limit: a 15 cu yd steel body of wet gravel can exceed 22 tons loaded, which sits at or above a 33,000 lb GVWR tandem chassis on most state bridge-formula checks, so length is chosen for payload weight first and volume second [S4]. Operators frequently use the dump truck capacity chart as a baseline when sizing a body against a known chassis rating.
Inside length: 14 to 16 ft is the volume sweet spot
Load King's 16 to 18 ft tri-axle dump ships as 16 to 19 cu yd at 88 in inside width and 48 in side height, which is the geometric baseline most tandem bodies are scaled down from [S2]. A common tandem length cited by working fleets is 14 to 15 ft inside, paired with a 96 in body, hitting roughly 10 to 12 cu yd struck before side boards [S7].
Heritage Truck Equipment offers steel dump bodies in any length from 9 ft to 24 ft, with material thickness from 4 mm up to 3/8 in AR-450, so a 14 to 16 ft body is a stock build with no custom surcharge [S3]. For heavier stone and riprap work, fleet spec sheets list 16 to 18 ft as the volume ceiling before bridge law forces a tri-axle reconfiguration [S2][S4].
Width, side height, and the cubic-yard geometry
Standard inside width on a tandem body is 88 to 96 in (7.3 to 8.0 ft). The Load King spec is 88 in inside / 84 in overall height with a 48 in side and a 54 in tailgate, which drops to roughly 16 cu yd on a 16 ft body when filled to the side wall (struck, not heaped) [S2]. Downeaster's XD class 6 to 8 dump lists 96 in body width across 119.5 in Lx86 in W x 24 to 30 in H variants, yielding 5.4 to 8.7 cu yd on a shorter body [S8].
Volume is calculated as inside length x inside width x inside height in feet, divided by 27 to convert cubic feet to cubic yards. A representative 15 ft x 8 ft x 4 ft body equals 480 cu ft, or about 17.8 cu yd gross; deduct 0.5 cu yd for the hoist well and another 0.5 cu yd if a curved-front radius is used, landing the realistic struck capacity near 16.8 cu yd [S1]. The same math, applied to a 14 ft x 96 in x 48 in body, yields 14.0 cu yd gross, which is the published target for most Class 8 tandem chassis.
Material thickness, steel grade, and structural ceiling
AR-450 is the working-industry floor steel for tandem bodies: Heritage's Model SP uses 3/16 in Hardox AR-450 floor, 5/32 in sides and bulkhead, and 3/16 in tailgate, while the Model HD steps every panel up by one gauge to 1/4 in floor, 3/16 in sides, and 1/4 in tailgate [S3]. Load King fits 1/4 in AR-450 across the floor, side sheet, front doghouse, and tailgate as standard on its 16 to 18 ft unit, which is the typical Class 8 / tandem ceiling for impact-loaded aggregate hauling [S2].
Floor thickness governs payload rating more than any other spec. A 3/16 in AR-450 floor handles roughly 12 to 14 tons of crushed stone in daily-cycle service; stepping to 1/4 in AR-450 (Model HD) extends service life into the 16 to 18 ton range before plate fatigue and impact denting become limiting factors [S3]. Hardox 450 in 3/16 in (4.8 mm) offers a Brinell hardness around 450 HBW and yield strength near 1,200 MPa, which is the working envelope most fleets accept for daily tandem use.
Side height, side boards, and effective volume
Standard side height on a tandem-class body is 36 to 48 in. Load King uses 48 in sides with a 54 in tailgate, giving 6 in of additional tailgate height to contain heaped asphalt without spillage [S2]. Most fixed-side contractor and landscape bodies sit at 12 to 30 in side height for Class 3 to 5 chassis; a 12 to 16 in side on a 9 to 12 ft drop-side body yields only 2.5 to 6 cu yd, which is well below tandem-class scale and is not a valid comparison point [S5].
Side boards (also called side extensions or boards) are common on tandems: 2 in x 8 in rough-cut lumber on top of the steel side adds 7 to 8 in of effective height, which can lift a 15 ft x 8 ft x 4 ft body from 14 cu yd to roughly 17 cu yd without changing the steel structure. Standard 2x8 boards are common because they match the Load King factory option list and do not require a re-rated hoist [S2].
Weight, tonnage, and why tandem bodies stop at 16 ft
A tandem (10-wheeler) chassis is typically legal for 12 to 16 tons of payload under state bridge laws, and that range, not yardage, is why the 14 to 16 ft body length is the upper limit for Class 8 tandems before tri-axle is required [S4]. Tri-axle chassis in 16 to 18 ft configuration are legal for 18 to 22 tons of asphalt or 20 to 25 tons of gravel, which is why fleet spec sheets for stone and riprap work default to tri-axle at 16 ft and above [S2][S4].
For reference: 1 cu yd of hot-mix asphalt weighs roughly 2 tons, so a 14 ft x 8 ft x 4 ft body at 14 cu yd struck is approximately 28 tons of asphalt, exceeding a tandem's legal envelope by 12 tons; the same body in dry mulch at 400 to 800 lb/yd³ would only weigh 2.8 to 5.6 tons, illustrating why material density, not body size, is the gating parameter for tandem trucks [S4]. Operators cross-check body length against chassis ratings with the mining dump truck reference when scaling up to articulated off-road units.
Side-by-side sizing comparison for tandem-class bodies
The three most common tandem-class bodies on the North American market, scaled against four decision criteria: [S5]
Load King 16 to 18 ft (tri-axle reference, applicable geometry to large tandems): 16 to 19 cu yd, 88 in inside width, 48 in side, 1/4 in AR-450 floor; the working choice for paving and stone contractors who can run tri-axle [S2].
Heritage Model HD 14 to 16 ft steel: 10 to 14 cu yd at 96 in width, 48 in side, 1/4 in AR-450 floor and 3/16 in sides; the working choice for tandem chassis running daily-cycle crushed stone at 14 to 16 tons [S3].
Downeaster XD 119.5 in body (about 10 ft): 5.4 to 8.7 cu yd, 96 in width, 24 to 30 in sides, 17 to 23 ton hoist capacity; this is the Class 6 to 7 lighter tandem / medium-duty choice, not a Class 8 tandem at 33,000 lb GVWR [S8].
The sizing takeaway: tandem bodies stop at 16 ft not because of steel strength but because of bridge law, with the 14 to 15 ft body on a 96 in x 48 in template being the most common Class 8 tandem build for 12 to 16 ton daily payload work [S3][S4].
Hoist, tailgate, and matching sub-components to body length
Body length drives hoist selection: a 14 to 16 ft tandem body typically uses a heavy-duty 6.5 in 4-stage trunnion-mounted telescopic hoist, rated for 17 to 23 tons of lift, which is the Load King factory fit and the Heritage standard trunnion or pin-to-pin option [S2][S3][S8]. The hoist well at the front of the body consumes about 0.5 cu yd of struck volume, which is a fixed loss independent of body length and should be subtracted from gross yardage before quoting a load [S1].
Tailgate options for tandem bodies fall into three buckets: air-release over-center (Load King standard), high-lift air-operated (for sticky clays and asphalt), and side-swing (for spreading aggregate in windrows). High-lift and side-swing tailgates add 100 to 250 lb to body weight and require the heavier-duty hoist option, so they are usually paired with the 1/4 in AR-450 floor of a Model HD-equivalent build [S2][S3]. Operators spec-ing concrete mixer truck chassis for comparison note the same hoist-class scaling logic applies when the drum support frame replaces the dump body.
Track the next two signals for tandem body sizing: (1) state DOT bridge-formula revisions affecting 33,000 to 40,000 lb GVWR tandem envelopes, which would shift the legal length ceiling; (2) AR-450 / Hardox 450 plate price index movements, since the 1/4 in floor option on a 16 ft body is the single largest material cost in a tandem-class build.
For related coverage, see Cupola Coke Bed Height: Spec for a Stable Combustion Zone.