Education in Motion / Clinical Corner / August 2017 / Understanding Seating Sizing

Understanding Seating Sizing

Getting the right fit is important in seating and mobility. The fit of the seating system can affect comfort, function, posture, and skin integrity. This month, Clinical Corner will focus on how to understand seating sizing for cushions, back supports and head supports. A few "tricks of the trade" will be shared so that clinicians can better understand how to request the correct size of seating for an individual.


It is commonly known that cushions are measured in width by depth, but what may not be as well-known is how to measure a cushion. In many cases, a more accurate measurement of a cushion is achieved by turning the cushion upside down and taking a measurement from the undersurface.

Some cushions are designed with cut-out notches at the posterior corners of the cushion. This allows for the cushion to be positioned between the back canes of the wheelchair. The notches help to secure the cushion on the wheelchair and to prevent movement of the cushion during transfers. Having part of the cushion sit between the back canes also provides support if the loading surface of the individual is posterior to the back canes. If growth is anticipated for an individual, the additional depth of the cushion allows for some lengthening in the cushion by moving the cushion forward to accommodate the individual's growth in length.

If a cushion is designed with cut-out notches, it is important to understand how to measure it. This is particularly important if measuring the cushion for a replacement cushion or cover. As the graphic below illustrates, the width measurement is made from the outside edge to the outside edge, represented by "X" on the graphic. The measurement includes the existing cover on the cushion. The depth measurement is taken from the front edge of the rear cut-out to the front bottom edge of the cushion, represented by "Y" on the graphic.

Back Supports

Back supports come in a multitude of heights and contours. When sizing a back support for an individual, it is important to think about the usable space, or contact area, within the back support. Due to the contour, or curve, of the back support, the flatter part of the back support where the posterior aspect of the individual's trunk makes contact with the support needs to be wide enough to provide the support required. Otherwise, an individual may not be getting the full support of the back support and may feel as though they are being pushed forward in the back support.

The graphic and chart below represents an example of a back support and is not to be used with all models of back supports for sizing. The graphic is a representative view of a back support, looking down from above. The graphic illustrates that even a back support with minimal contour (2.2 inches in this case) will not allow an individual to sit fully into the back support if it is not sized appropriately.

To obtain the correct size of back support for an individual, the anatomical measurement must be taken of the widest part of the individual's trunk that will be supported by the back support. It is important to note that the anatomical measurement of the individual may not be the same as the measurement of the back support, as the above chart illustrates. For example, if a person's trunk measured 16 inches in width and a 16 inch wide back support was ordered in this particular model, the back support would not fit the individual. If in doubt, ask the manufacturer about the actual sizing of their products to ensure the correct fit.

The above chart also illustrates another factor that is important to consider when selecting a back support for an individual. It is important to size the back support for the individual, not the wheelchair. Some models of back supports can fit onto different back cane widths through hardware adjustment. For example, both a 16 inch wide and an 18 inch wide back support can fit onto an 18 inch wide wheelchair. If a 16 inch wide back support is installed on an 18 inch wide wheelchair, but the person requires the 18 inch wide back support, the person will not immerse into the back support and will not have full contact with the back support. Conversely, if an 18 inch wide back support is installed on an 18 inch wide wheelchair, but the person requires a 16 inch wide back support due to a narrow trunk and wider hips, the person's trunk will not be adequately supported. Sizing the back support for the individual and not the wheelchair allows for the proper postural support for the individual.

Head Supports

Just like back supports have useable space, head supports have useable space as well. A single pad head support is curved. The longer the single pad, the greater the contour to provide the head with support is needed.

The graphics below represent examples of single pad head supports and are not to be used with all models of head supports for sizing. Head supports are measured along the posterior aspect of the pad; that is, taking a cloth tape measure and following the outer curve of the pad. The graphic pairing below on the left represents an 8 inch pad. There is one inch of depth contour within the 8 inch pad, with 5.5 inches of useable contact space within the pad. The graphic pairing on the right represents a pad that measures 14 inches along the outer perimeter of the pad. The depth of contour of the pad has increased to 2.5 inches with 4 inches of width being available at the narrowest part of the curve. Understanding these measurements helps to ensure the correct fit for the size of the client's head and taking into account the need for lateral support.


This month, Clinical Corner has looked at the sizing of cushions, back supports and head support pads. By understanding how a manufacturer sizes seating products, the correct fit for an individual can be obtained. The correct fit is vital for comfort, function, posture, and skin integrity.

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