## How to Calculate The Bulking Volume Of Excavated Spoil

We show you how to calculate the true value of excavation when digging earthworks projects.

Article By: Tom Ayre | Last Update: November 2020

Calculating bulking factors are an important element in earthworks / excavations projects big and small.

Having removed a small amount of earth in my garden I was surprised at how much volume the soil bulked out to. I had to hire a grab lorry as the volume would have been too much for a skip! When working on a large earth moving project it is even more critical to calculate this correctly.

Fun fact, the deepest hole ever dug was 7.5 miles into the earth, that’s a lot of soil!

Knowing the volume of material after an excavation has taken place is important because:

- Calculating accurate costs for removing material (muck away).
- Working out how and where to store the material.
- Factoring in the right amount of time to deal with the material.

In this blog article I will explain how bulking factors work, how to calculate by hand and give you a free to use calculator tool that will help with:

- Calculating bulking factor volume.
- Calculating how many trips to remove the material (muck away).
- Calculating how much storage you need.

Let’s get started!

### Table of Contents

### What Are Bulking Factors?

A bulking factor is a number that is multiplied by the volume of material to get a true reflection of the uncompacted volume.

Having removed a small amount of earth in my garden I was surprised at how much volume the soil bulked out to. I had to hire a grab lorry as the volume would have been too much for a skip! When working on a large earth moving project it is even more critical to calculate this correctly.

To use a bulking factor number you have to multiply the bulking factor number by the excavated volume size.

For instance, a bulking factor for Clay and Gravel is typically 1.15

If your excavation was 15 m3.

Your volume size would be 1.15 x 15 = 17.25 m3

You must consider the bulking factor of the material you are digging to ensure you correctly plan for the removal costs and time to do it in.

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### What Are Diggability Factors?

Each material that you excavate will have different properties in terms of how easy they are to dig.

The most common way of categorising a soils digability or ease of digging is:

- E = Easy digging – Loose free-running soils eg sands, fine gravels.
- M = Medium – Denser cohesive soils eg clayey gravel, low PI clays
- M-H = Medium to Hard – eg broken rock, wet heavy clay, gravel with boulders
- H = Hard – material requiring blasting and hard high PI clays

In our calculator below, you will see the materials digability using the “E”, “M”, “M-H”,”H” format.

### Calculate Spoil Bulking Volume

Use this tool to:

- Calculate bulked out / excavation volume
- Calculate how many trips to remove (muck away) the material.
- Calculate how many storage units to store the material.

### How To Calculate Volume Size

When calculating your volume size you will need accurate measurements. Depending on the size of the project it might be worth hiring a topographical survey company to measure the area / volume precisely.

**Rectangular Excavation**

Volume = W x H X L

Example = 1.5 x 2 x 8

= 24 m3

**Cutting Excavation**

Volume = ((H * W1) / 2) + (W2 * H) + ((H * W2) / 2)) * L

Example = ((0.5 * 0.3) / 2) + (1.5 * 0.5) + ((0.5 * 0.3) / 2)) * 2.1

= 1.89 m3

For more complicated volumes, use an online calculator such as the one here.