Dump truck capacity (cubic yards and tons): which limit hits first
Steve Woods · Lead Dispatcher, TruckSprint
Steve Woods leads the TruckSprint dispatch desk and reviews every guide we publish. How we research and update guides.
Updated October 2026
Quick answer
A dump truck's capacity is the smaller of two numbers: the volume its body holds (inside length x width x height / 27 = cubic yards) and the weight it can legally carry (legal gross minus empty weight). With heavy materials like gravel at about 1.42 tons per cubic yard, the weight limit usually hits first, well before the body is full.
Source: NM EMNRD conversion factors; 23 CFR 658.17 · checked 2026-10
Every dump truck owner learns this the expensive way: a "20-yard truck" doesn't haul 20 yards of gravel. It hauls what the scale allows. Here's how to work out both numbers for your own truck, and which one decides.
Cubic yards: measure the body yourself
Struck capacity is simple geometry. Measure the inside of the body in feet:
Struck cubic yards = inside length x inside width x side height / 27
| EXAMPLE body (inside) | Struck capacity |
|---|---|
| 10 ft x 7 ft x 2.5 ft | 6.5 yd³ |
| 14 ft x 7.5 ft x 3.5 ft | 13.6 yd³ |
| 16 ft x 7.5 ft x 4.5 ft | 20.0 yd³ |
| 18 ft x 7.5 ft x 5 ft | 25.0 yd³ |
These are example dimensions, not a manufacturer's ratings. Tapered or rounded bodies hold a little less than the box math; the body maker's spec sheet gives the rated number.
Heaped capacity adds the mound above the sides. How much depends on the material's angle of repose and the loader, so it isn't a fixed percentage. Use the maker's heaped rating if you have it, or your own estimate.
Tons: the legal payload decides
Legal payload = legal gross weight - empty weight.
Legal gross depends on your axles, the distance between them and the road. On the Interstate System, federal law caps any one axle at 20,000 lb, a tandem at 34,000 lb, and the whole truck at the Bridge Formula's limit for its axle count and spread, up to 80,000 lb.
Source: 23 CFR 658.17 (FHWA) · checked 2026-10
That's why short dump trucks run out of legal weight early. A 3-axle tandem dump with about 20 ft between its steer and rear axles is held to 51,000 lb gross by the Bridge Formula on the Interstate, however strong its frame. Off the Interstate, your state's limits apply, and many states allow dump trucks more under their own rules or grandfather provisions. Check yours with the Bridge Formula calculator and your state DOT.
Empty weight comes from a scale ticket with full fuel and the driver aboard. Don't trust the spec sheet; bodies, liners and tarps add up.
Converting yards to tons
Materials weigh different amounts per loose cubic yard. Published conversion factors give a starting point:
| Material | Tons per loose cubic yard | Source |
|---|---|---|
| Gravel (1/4 to 2 in) | 1.42 | NM EMNRD |
| Sand | 1.45 | NM EMNRD |
| Base course | 1.25 | NM EMNRD |
| Loose aggregate (estimating) | 1.4 | Missouri DOT |
| Topsoil | 0.8 | NM EMNRD |
| Fill dirt | 0.8 | NM EMNRD |
Source: New Mexico EMNRD, Mining and Minerals Division, conversion factors · checked 2026-10
Source: Missouri DOT Engineering Policy Guide, estimate factors · checked 2026-10
Moisture and gradation move these numbers, sometimes a lot. Wet sand and clay can be much heavier. The scale ticket is the real answer; use the table to plan, then confirm on the first load.
Which limit hits first? Run your truck
Put in your body's inside dimensions, the material and your truck's numbers. The calculator shows the struck and heaped yards, what that much material would weigh, and the most you can legally haul.
Dump truck capacity calculator
- Struck capacity
- 20.0 yd³
- Heaped (+10%)
- 22.0 yd³
- Heaped load would weigh
- 31.2 tons
- Legal payload
- 12.0 tons
- Most you can haul legally
- 12.0 t · 8.5 yd³
Weight hits first: stop at about 8.5 yd³ of this material, even though the body holds more.
Densities: published conversion factors (NM EMNRD, MoDOT), checked 2026-10. Moisture changes them; the scale ticket is the real answer. Check your axle limits and state rules too.
Worked example: a 20-yard tandem hauling gravel
| EXAMPLE | |
|---|---|
| Body, inside | 16 x 7.5 x 4.5 ft = 20 yd³ struck |
| Heaped (+10% estimate) | 22 yd³ |
| 22 yd³ of gravel would weigh | about 31 tons |
| Legal gross (Interstate, 3 axles over 20 ft) | 51,000 lb |
| Empty weight (scale ticket) | 27,000 lb |
| Legal payload | 24,000 lb = 12 tons |
| Most gravel you can haul legally | about 8.5 yd³ |
The body could hold more than twice what the truck can legally carry. With topsoil at about 0.8 tons per yard, the same truck still reaches 12 tons at 15 yards. Only very light material, like mulch, fills the body before the scale says stop.
What it means for your day
Capacity per load sets your loads per day, and loads per day set what you earn on per-ton or per-load work. If you're paid by the hour, capacity matters less to your pay but still decides how many trucks a contractor needs. Either way, overloading to stretch a load is the fastest way to lose a day: a scale ticket over the limit means fines, a forced unload and sometimes an out-of-service order. Quote and load to the legal number.