Backfill Calculator
How much fill a trench needs once the pipe or structure is in, in loose volume, tonnes and truck loads.
Results
Volume still to fill
16.7000
m³
Volume dug out
19.2000
m³
Loose volume to order
20.8750
m³
Mass of the fill
30,060.0
kg
The same in tonnes
30.060
t
Loads to bring in
3
Surplus to take away
3.1250
m³
Share of the trench it takes
13.02
%
Cross-section of the trench
0.9600
m²
What this tool does
Dug soil does not go back in the same hole: it comes out loose and takes up more room than it did in the ground. The ratio between the two is the bulking factor, and forgetting it is why deliveries come up short. This page takes the structure out of the trench volume first, then applies the bulking factor to what is actually left to fill.
Formula
volume to fill = excavation − structure · loose material = volume to fill × bulking factor · loads = ⌈loose ÷ capacity⌉
Variables
| Symbol | Meaning | Unit |
|---|---|---|
len | Trench length | m |
wid | Trench width | m |
dep | Trench depth | m |
vs | Volume of what is already in it | m³ |
bf | Bulking factor, loose over in place | — |
rho | Density of the material | kg/m³ |
tc | Capacity of one load | m³ |
VB | Volume still to fill | m³ |
VE | Volume dug out | m³ |
VL | Loose volume to order | m³ |
MA | Mass of the fill | kg |
TO | The same in tonnes | t |
NT | Loads to bring in | — |
SU | Surplus to take away | m³ |
PC | Share of the trench it takes | % |
SE | Cross-section of the trench | m² |
Worked example
- Trench length20 m
- Trench width0.8 m
- Trench depth1.2 m
- Volume of what is already in it2.5 m³
- Bulking factor, loose over in place1.25
- Density of the material1800 kg/m³
- Capacity of one load8 m³
- Volume still to fill16.7000 m³
- Volume dug out19.2000 m³
- Loose volume to order20.8750 m³
- Mass of the fill30,060.0 kg
- The same in tonnes30.060 t
- Loads to bring in3
- Surplus to take away3.1250 m³
- Share of the trench it takes13.02 %
- Cross-section of the trench0.9600 m²
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.
- Mixing units is the most common source of error. Convert every input to the units shown next to each field before calculating.