How to Calculate Bulking Factor for Earthworks Projects

We show you how to calculate earthworks bulking factors as well as calculators for removing and storing material.

Article By: Tom Ayre
Last Update: May 2020

Calculating bulking factors are an important element in earthworks projects. Knowing the volume of material after an excavation has taken place is important because:

  • Calculating accurate costs for removing material.
  • 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
  • Calculating how much storage you need.

Let’s get started!

A Brief Introduction to Bulking Factors

Bulking is simply the increase in the volume once the material has been excavated from its location.

When the material is in the ground it is typically tightly compacted together. When exposed and dug from the ground the compactness is relieved and the volume of the material increases.

To calculate this increase in soil volume you can use a bulking factor number, typical values can be easily found however the calculation for it is:

bulking factor = volume after excavation / volume before excavation

For example:

Volume after = 25m3

Volume before = 15 m3

Bulking factor = 25 / 15

= 1.666

How To Calculate Bulking Density By Hand

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.

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.

Earth Movement / Bulking Calculator

Use this form to:

  • Calculate bulked out volume
  • Calculate how many trips to remove the material.
  • Calculate how many storage units to store the material.


How To Calculate Volumes

Rectangular Excavation

Volume = W x H X L
Example = 1.5 x 2 x 8
= 24 m3

rectangular cross section volume calculator

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

Cross section excavation diagram

Hopefully, this explains what a bulking factor is and how important they are in earthworks projects. If you have any questions or queries I can help with then please let me know in the comments section. Happy to assist!


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By |September 11th, 2019|Calculators|0 Comments

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