Sizing a dump truck: payload, body volume and material density

“Dump truck, 20 cubic metres” describes a body, not a truck. Buyers who specify by body volume alone regularly end up with a machine that is either overloaded or wasting half its legal payload. This guide explains the relationship between payload, body volume and material density, and how to turn your tonnage requirement into a truck and fleet specification.

Payload versus body volume

• Payload (rated in tonnes or kilograms) is set by the chassis: axle ratings, suspension, frame and tyres. It is a legal and structural limit — exceeding it is not a performance question, it is a safety and compliance one.
• Body volume (in cubic metres, struck or heaped) is a geometric property of the tipper body. How many tonnes that volume actually carries depends entirely on the material.

A body correctly matched to light material will be far too large for dense material: the truck hits its payload limit at a third of a load. The correct sequence is to start from the tonnage you need to move and the material you are moving, then size the body.

Material density does the maths

Typical loose (bank or stockpile) densities for common construction materials sit in ranges like these — published engineering ranges, not a quotation:

Material	Typical loose density (t/m³)
Dry topsoil / loose fill	1.2 – 1.5
Sand, dry	1.4 – 1.7
Gravel, crushed stone	1.5 – 1.9
Wet clay / heavy soil	1.8 – 2.1
Broken rock / hard quarry rock	1.6 – 2.0

Two caveats matter in practice. First, moisture content moves density significantly — the same sand can be a different material after rain. Second, “struck” (level) and “heaped” (with the load piled above the sides) volumes differ by roughly 10-25% depending on body shape, and quotes must state which one they use. If your project works to tonnes per shift, send the material and the tonnage; if it works to loads per shift, send both loads and material.

Matching the truck to the loader

On loader-fed sites the pair has to work as a unit:

• Three to five passes of the loader bucket per truck load is the usual planning range. More passes means the loader is undersized; fewer means it is oversized.
• The loader must reach over the truck body at full height without the operator straining the machine.
• Truck size, body height and the loader’s lift height and dump clearance are one specification, not two.

From cycle time to fleet size

Truck numbers follow from arithmetic, not preference:

1. Tonnage per hour needed — your production target.
2. Cycle time — load time, haul time at the site speed limit, tipping, and return. Gradients, road condition and traffic control all change this.
3. Trucks required = tonnage per hour needed × cycle time ÷ payload per truck, adjusted for availability (a truck in maintenance or stuck in traffic is not moving material).

Under-trucking a shovel or loader is as wasteful as under-loading a truck: the excavator waits, and the whole chain runs at the speed of its scarcest unit. Over-trucking just moves the queue to the loading point.

Road-going or site-only?

Before comparing models, settle what the trucks must legally be:

• On-road trucks are constrained by axle-load limits, dimensions, braking and lighting rules that differ by country and region. Road registration and any homologation paperwork belong in the inquiry from the start.
• Site-only or in-mine trucks can be built for heavier payloads and rougher conditions, but they cannot simply be driven onto public roads.

A truck that is excellent for a quarry loop can be illegal to drive to it.

What to send with your inquiry

1. Material and its density (or material type and moisture conditions).
2. Target tonnage per hour or per shift.
3. Haul distance, gradients and road surface.
4. Loading method: loader, excavator, or conveyor feed.
5. Body type needed: rear dump, and whether a flat deck or other body configuration fits the work.
6. Destination country and any road or emission requirements that apply.

An honest word about this guide

The density ranges above are general engineering guidance, not measured data for your site. Rated payloads, body volumes and legally available configurations differ by model, market and order — they are confirmed in the quotation, per order, against the machines that can genuinely be supplied.

Send us the six items above and we will size the truck and body configuration we can actually offer for your material and route.