Trucks per excavator calculator
- Trucks needed
- 4.75
- Passes per truck
- 5
- Loading time
- 2.0 min
- Truck cycle time
- 9.5 min
| Trucks | Match factor | Loads per hour | m³ loose per hour |
|---|---|---|---|
| 3 | 0.63 | 18.9 | 284 |
| 4 | 0.84 | 25.3 | 379 |
| 5 | 1.05 | 30.0 | 450 |
| 6 | 1.26 | 30.0 | 450 |
Passes are rounded up to whole buckets, and the rates are theoretical. Real production is lower, so allow for job efficiency.
The basic idea
An excavator loads one truck at a time. While it's loading one, every other truck is hauling, dumping, coming back or waiting. You need enough trucks to keep the excavator loading, but not so many that they pile up behind it.
- Trucks needed = truck cycle time ÷ loading time
The worked example below follows one excavator loading one fleet of trucks.
Step 1: Loading time
- Passes per truck = truck load ÷ loose volume per bucket
- Loading time = passes per truck × excavator cycle time
Say the excavator carries 3.0 m³ loose per bucket and the trucks carry 15 m³ loose. That's 15 ÷ 3.0 = 5 passes. At 24 seconds per pass, loading takes 5 × 24 = 120 seconds, or 2.0 minutes.
Passes are whole numbers, so round to what actually happens: an extra pass, or a slightly light load. Check the load against the truck's rated payload too. With heavy material, the truck can reach its weight limit before it's full.
Step 2: Truck cycle time
A truck's cycle is everything from the start of one load to the start of the next.
| Part of the cycle | Working | Minutes |
|---|---|---|
| Load | From step 1 | 2.0 |
| Haul (loaded) | 1.2 km at 20 km/h | 3.6 |
| Dump and turn | Allowance | 1.0 |
| Return (empty) | 1.2 km at 30 km/h | 2.4 |
| Spot at the excavator | Allowance | 0.5 |
| Cycle time | 9.5 |
Travel time in minutes is distance ÷ speed × 60. Use average speeds that allow for accelerating, braking, corners, grades and the haul road surface, not the truck's top speed.
Step 3: Number of trucks
9.5 ÷ 2.0 = 4.75. On paper, the right fleet is between 4 and 5 trucks. To choose between them, use the match factor.
Step 4: The match factor
- Match factor = (number of trucks × loading time) ÷ (number of excavators × truck cycle time)
A match factor of 1 is balanced in theory. Below 1, the excavator waits for trucks. Above 1, trucks wait for the excavator.
- 4 trucks: 4 × 2.0 ÷ 9.5 = 0.84. The excavator waits about 16% of the time.
- 5 trucks: 5 × 2.0 ÷ 9.5 = 1.05. The trucks wait a little.
Step 5: Production
The excavator can't load more than 60 ÷ 2.0 = 30 loads an hour. The trucks can't carry more than trucks × 60 ÷ cycle time. Production is whichever is lower.
| Trucks | Match factor | Loads per hour | m³ loose per hour |
|---|---|---|---|
| 3 | 0.63 | 18.9 | 284 |
| 4 | 0.84 | 25.3 | 379 |
| 5 | 1.05 | 30.0 | 450 |
| 6 | 1.26 | 30.0 | 450 |
The fifth truck lifts production from 25.3 to 30 loads an hour, about 19% more for 25% more trucks. A sixth adds nothing: the excavator is already flat out. Whether the fifth truck pays depends on what a truck-hour costs compared with an hour of excavator and operator standing idle.
These are theoretical rates. Real production is lower, so allow for job efficiency (a 50-minute working hour is a common starting point), and convert loose volume to bank or compacted volume using the material's swell and shrinkage.
Why the calculation only gets you close
The calculation uses averages, and an earthworks site isn't average.
- Cycle times vary. A truck waits at the gate, one driver is slower than the others, and the loading position moves.
- Trucks bunch. Even with a match factor below 1, trucks arrive together and queue, then the excavator sits idle waiting for the next one. Averages hide this.
- The haul changes. As the cut and fill areas move, the haul gets longer or shorter, and so does the cycle time.
- Conditions change. Rain slows the haul road, and a breakdown takes a truck out of the cycle.
Treat the calculation as a starting point, and check it against how the job actually runs on site.