Seat Depth Explained: Why The Correct Depth Is Crucial For Comfort

As covered in previous blogposts, seat sizing is fundamental to good posture in seating.

Seat depth is the distance between the front of the seat cushion and the backrest, usually measured in inches for specialist seating. A standard seat depth is usually between 18 and 22 inches, with a finger-width gap between the front of the seat and the back of the knee, with the person’s feet resting flat on the floor or footplate.

In this article we take a closer look at seat depth and why it is such a crucial metric in seat sizing.

Jump straight to…

• • How important is seat depth?
  • How to measure seat depth
  • What other qualities are important for comfort?
  • How to choose a chair with the right seat depth
  • Frequently Asked Questions (FAQs)

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.

This can often be the case with sofas that are too deep, making standing up harder and leaving the lower back unsupported. Extra pillows and cushions may be used to try to remedy this, but not support the user or distribute pressure properly.

A rise recliner chair or sofa that is made-to-measure will make sitting and standing up from the chair so much easier for an older person, than a deep sofa they ‘sink into’ and may struggle to get out of.

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.

How to choose a chair with the right seat depth

To make sure you get the right seat depth in your chair, it’s recommended to speak to a seating specialist who can measure you up and provide a chair with the correct seat dimensions.

Another option, and one provided by many council loan stores, is seating that can be adjusted to different sizes using toolless adjustment mechanisms, such as our Lento seating range. Your OT or seating specialist can set this to the right dimensions for you on delivery, with instructions on how to adjust in the future if needs change.

The great advantage of adjustable chairs like the Lento range is that they are fully adjustable to suit the largest range of users possible, cutting down on cost and duplication within hospitals and community loan services by being able to reuse and resize the chair for each individual person.

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.

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.