How to calculate cartage and aggregate delivery costs

1. Start with the actual material quantity

Supply cost is the quantity delivered multiplied by the agreed material rate. Do not increase the purchased quantity just because the truck has spare capacity on its final trip. If the rate is per tonne and the job quantity is in cubic metres, convert the volume using an appropriate material density first.

Tonnes = cubic metres × density in tonnes/m³
Supply cost = actual tonnes × price per tonne

Density varies with material, grading and condition. Check it with the supplier rather than treating a generic conversion as exact. Keep the rate, density and units visible in your working notes.

2. Use the vehicle’s effective payload

A load may be limited by weight or body capacity. Multiply usable cubic metres by density to find the volume-limited weight, then use the smaller of that and the configured weight payload. Confirm the actual vehicle, trailer and route constraints; a quoting calculator does not certify legal loading capacity.

Effective tonnes per load = lower of weight payload and volume capacity × density
Charged trips = round up(actual tonnes ÷ effective tonnes per load)

A final partial load still takes a complete dispatched trip. Charge its full cartage allowance, but only the material quantity actually supplied. For separately carried commodities, calculate each product’s trips separately; do not assume two partial loads can share a vehicle.

3. Include the complete return journey and handling

Estimate return driving time and add loading, unloading and repeatable stop allowances for each load. Keep one-off depot travel or a one-time delay separate, so it is not multiplied by every trip.

Driving hours per trip = complete return kilometres ÷ average km/h
Trip hours = driving hours + loading hours + unloading hours + repeatable allowances
Freight cost = charged trips × trip hours × hourly cartage rate + one-off cartage

If a map provides a reference duration, choose that or a manual allowance; do not count both for the same base journey. Check access, road conditions, queues and stops. A road-map estimate is not necessarily a truck-suitable route.

4. Check a worked example

This fictional example uses one material, a 10.5-tonne effective payload and the same return journey per load. Amounts are illustrative NZD, excluding tax—not a current supplier or freight offer.

The tenth load costs $171.60 in material (5.5 × $31.20), plus the full $160 trip allowance. Total vehicle hours are accumulated operating time, not a promise that multiple trucks will finish in ten elapsed hours.

5. Turn cost into a customer selling price

Margin and markup are different. A 20% margin means cost represents 80% of selling price. Multiplying cost by 1.2 gives a 20% markup, not a 20% margin.

Selling price before tax = estimated cost ÷ (1 − margin percentage ÷ 100)

Here, $4,956 ÷ 0.8 gives $6,195 before tax. Review tax treatment separately for your company and customer; internal supply and cartage calculations remain tax-exclusive.

Before issuing the quote, check quantities, currency, payload, complete return time, repeated versus one-off allowances, price validity and site conditions. Show your customer the selling price and terms, not your private costs and margin. Save a version so later price changes do not rewrite what you offered.

Common quoting questions

Should every value be rounded up?

No. Round dispatched loads up to a whole trip. Keep quantity and cost precision in the calculation; display distances and times in readable units without silently changing the estimate.

Does the final load get cheaper freight?

Not in this per-trip model. A part load still uses the full trip allowance. Only its material cost falls with the smaller quantity. Use a different agreed freight model only when it reflects the actual arrangement.