As covered in previous blogposts, seat sizing is fundamental to good posture in seating.
In this article we take a closer look at seat depth and why it is such a crucial metric in seat sizing. For clarity, when referring to seat depth we mean the distance between the front of the seat cushion and the backrest.
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How important is seat depth?
The correct seat depth ensures your back stays supported while your legs rest comfortably in the chair. The way to get the correct seat depth measurement is to ensure that the seat supports the entire upper leg all the way to the knee without putting pressure on the back of the calves. You should be able to get a finger’s width between the chair and the back of the knee.
It is crucially important to correctly measure seat height and depth when specifying specialist seating solutions.
Having a seat that is too shallow or too deep can cause discomfort in the following ways:
Too short
A seat that is too shallow pushes the user forward out of the chair, with their legs hanging over the front edge of the seat. This creates more pressure on the upper thighs and buttocks, which can potentially lead to pressure injuries. It can also reduce trunk control, with the user leaning forward or sideways to steady themselves, without adequate support in the seat base.
They may also slant their legs to the side to secure themselves in the chair, creating a ‘windswept leg’ posture and decentralising the pelvis.
Too deep
If the seat is too deep, this will encourage slouching, with the person’s sacrum positioned further from the backrest.
Pressure can build up in the coccyx area and on the back of the calves if the seat is too deep.
How to measure seat depth
For the correct seat depth, measure from the bottom of the spine (sacrum) to the back of the knee, while the person is sat upright in a chair with their lumbar region against the backrest. Allow at least a finger’s width between the chair and back of the knee.
What is the depth of a typical seat?
A seat depth of 20 – 22 inches is normal for average-height people between 5’4” and 5’10”. People six feet or more would have a seat depth of 23 to 24 inches.
What other qualities are important for comfort?
Of course, without the correct seat width and height, the seat would still be uncomfortable for the user, so all these metrics are important to get right and form the base of a comfortable chair.
Next, we can look at whether the client needs extra cushioning or support, such as in the lumbar section, headrest, armrests or legrest, depending on how much they use the chair and how sensitive they are to skin pressure.
They may need extra lumbar support to support their upper body, which a soft lumbar cushion works well for and can be repositioned to make the user more comfortable.
Lateral backrest – Lento Care Chair
How to choose a chair with the right seat depth
The great advantage of our Lento range is that the seat depth is adjustable, which is why the Lento was created in the first place, to provide a chair that was fully adjustable to suit the largest range of users possible, with easy toolless adjustment.
If you are looking for a made-to-measure armchair or riser recliner, we have published guides like our Seat Sizing Guide, which OTs and therapists alike find extremely useful when conducting seating assessments.
Book a Seating Assessment
If you go for an adjustable Lento chair such as the Lento care chair or riser recliner, you can find the correct seat depth for you anywhere between 14 and 22 inches and lock it in at this measurement for your own bespoke seat size.
Explore the Lento Range
Frequently Asked Questions (FAQs)
Q: Why is the correct seat depth so important?
A: A seat that’s too shallow forces you forward and increases pressure on the thighs and pelvis. A seat that’s too deep encourages slouching and puts strain on the coccyx.
Q: What is the typical seat depth for most people?
A: For adults between 5’4″ and 5’10”, a seat depth of about 20–22 inches works well. Taller users, around six feet or more, often need 23–24 inches.
Q: What if more than one person uses the same chair?
A: An adjustable seat depth is the best solution. Chairs like the Lento range allow you to slide the seat forward or backward – typically between 14 and 22 inches – so each user can lock in a custom fit.
Q: Are other chair dimensions just as important?
A: Yes. Seat width, seat height, and features such as lumbar support, armrests, and cushioning all play a role in overall comfort and posture.
Ralph has many years' experience in the healthcare sector. In a previous life he worked in finance, and his spreadsheet skills come in handy for all the analysis and research he does as he investigates topics and solutions for some of the world's most complex healthcare conditions and challenges. Aside from writing in-depth articles and organising webinars and interviews with top healthcare professionals, Ralph also administrates Vivid's "Healthcare Pioneers Board", a large group of healthcare specialists with multiple disciplines, who are working together to improve care for years to come.
