Picking an excavator? Don’t overlook digging depth

When picking an excavator, people usually focus on things like engine power, size, or how big the bucket is. But one important detail that’s often missed is how deep it can dig.

If the machine can’t reach the right depth, you could run into problems, like unfinished work, extra costs, or needing to bring in another machine.

In this article, we’ll look at why digging depth matters, what affects it, and how to choose the right excavator for the job based on what’s really needed, not just what’s written in the specs.

What is digging depth and why does it matter?

Digging depth refers to the maximum vertical distance the excavator bucket can reach below the ground surface. It’s a core performance metric, particularly in applications like trenching for utilities, foundation excavation, basement construction and drainage installation.

Inadequate reach can result in unfinished trenches, sloped excavation (not vertical) and multiple repositionings of the machine.

On the flip side, over-specifying depth can lead to higher costs and underutilization of machine capability. Therefore, understanding what influences an excavator’s digging depth is essential for selecting the right machine and optimizing its performance on the job site.

Key factors affecting an excavator's digging depth

Several technical and mechanical elements determine how deep an excavator can dig. These must be carefully assessed before selection or purchase.

1. Boom and arm configuration

The boom and arm (also called dipper or stick) determine the geometry of the digging arc. Long-reach arms provide extended digging depth but reduce lifting capacity.

• Standard boom + short arm: Better for lifting, faster cycle times.

• Long boom + long arm: Ideal for deep trenching, canals, or marine applications.

For instance, The Kobelco SK350LC-10 medium excavator has a maximum digging depth of 7.56 meters when equipped with the standard 6.5-meter boom and a standard arm. This depth is suitable for medium to large-scale excavation tasks, such as foundation work, utility trenching, and road construction. 

2. Machine size class

Excavators are broadly classified as:

• Mini excavators (1–6 tons): max depth: 1.5m to 4m

• Midi or compact excavators (6–10 tons): max depth: 3.5m to 5.5m

• Standard/medium excavators (10–40 tons): max depth: 5.5m to 7.5m

• Large excavators (40+ tons): max depth: 7.5m to 10m+

• Long-reach or specialty excavators: custom setups can dig over 15m

Selecting the wrong machine size can lead to poor performance or unnecessary costs. For example, the Volvo EC550EL is a powerful, large excavator, perfect for major earthworks or deep trenching, but too large and heavy for small-scale jobs like residential sewer lines. 

In those cases, a Cat 303E or Cat 305.5E2 mini excavator would be a better fit due to their compact size and maneuverability.

3. Undercarriage stability and counterweight

Digging depth is only effective if the machine remains stable. Long-arm setups require heavier counterweights and reinforced undercarriage.

Machines like the Volvo EC550EL are built for deep excavation with reinforced undercarriages and heavy counterweights that ensure stability, even with long-reach arms or under full load conditions.

4. Hydraulic system pressure and flow

Even if the geometry allows deep digging, the hydraulic system must support the force required to cut and lift material at full reach. Systems must maintain power at maximum extension, especially in hard soil.

How to evaluate the right digging depth for your project?

Before selecting a machine on makana.com or anywhere else, contractors typically assess project-specific factors. Here’s what they look at:

1. Project type and excavation design

A trench for telecom cables may need just 1.2 meters depth, while a commercial building foundation could require 5 meters or more. Always match machine capability with the approved excavation drawings.

2. Soil conditions

Soft clay is easier to dig through than compacted rock or frozen ground. The harder the soil, the more power is required at depth.

Tip: Use certified +70 points inspection reports available on makana.com to check if the machine’s hydraulics have been tested under full load.

3. Space constraints on site

Urban sites often have tight access, restricting swing radius and positioning. Mini excavators with lesser depth might be more productive due to maneuverability.

For example, a Cat 303E mini excavator digs up to 2.6 meters, making it a great fit for tight urban jobs where space is limited. In contrast, a Volvo EC550EL can reach over 7.5 meters, but needs much more room to operate due to its size and swing radius.

4. Slope or bench requirements

If the ground isn’t strong enough to dig straight down, workers need to dig in steps or layers (benches) instead, kind of like stairs. Because of this, the excavator arm might need to reach further to dig deep enough from a safe distance. This consideration highlights the importance of distinguishing between two key concepts in excavation operations: the digging depth and digging reach?

What is the difference between digging depth and digging reach?

Digging depth and digging reach are often confused, but they mean different things, and both matter when choosing the right excavator.

• Digging depth is how far down the bucket can go from ground level when fully extended. For example, the Volvo EC550EL can dig over 7.5 meters deep, making it ideal for large foundations or deep trenching. The Kobelco SK350LC-10 also offers solid depth, around 7.3 meters, suited for general construction.

• Digging reach is how far the bucket can stretch out horizontally from the center of the machine. This is important when you can’t reposition the excavator easily, like working next to a road, a building, or inside narrow sites. A Cat 303E mini excavator has a smaller reach but works well in tight urban spaces where maneuverability matters more than depth.

Here’s a tip: always check both depth and reach against your site plan before choosing a machine.

Which excavator has the deepest digging depth in the world?

When it comes to extreme digging performance, the Type Es 3750 bucket-chain excavator, developed by TAKRAF, holds the record for the deepest digging depth among all machines, reaching up to 31.2 meters. 

This machine isn’t used in conventional construction, but rather in open-pit mining where ultra-deep excavation is required.

For more recognizable equipment types, the Bagger 288, a bucket-wheel excavator and one of the world’s largest heavy machinery, offers a digging depth of around 30 meters, though it operates on a different excavation principle.

In the category of hydraulic long-reach excavators, commonly seen in construction and marine works, the SANY SY265C Long Reach delivers a maximum digging depth of over 13 meters, placing it among the top-performing machines in its class for reach-focused applications.

These extremes highlight the vast range of excavator configurations and underscore why specifying depth correctly matters; overestimating or underestimating can drastically affect productivity, fuel use, and even site safety.

How to inspect used excavators for digging depth capability?

When buying a used excavator, it’s important to verify that the machine’s digging depth specs are still valid. Key checks include:

• Cylinder stroke test: Fully extend the boom and arm; check for smooth operation without jerks.

• Linkage play: Excess movement in bucket linkages can reduce effective digging depth.

• Hydraulic pressure test: Confirms the machine can maintain force at full extension.

• Undercarriage balance: Worn tracks or uneven sprockets can destabilize the unit during deep trenching.

Conclusion

Digging depth is not just a number, it’s a performance boundary that defines what an excavator can achieve on-site. Evaluating it goes far beyond brochures. Contractors need to consider geometry, hydraulics, attachments, site conditions, and real-world machine condition.

When browsing machines on makana.com, use certified inspection reports or book a virtual tour to ensure that the machine's configuration and condition meet your digging depth requirements, saving you both time and costly missteps.