It is important that the measurements you take are consistent, accurate and clearly communicated.

Be clear whether the measurements you are providing are that of the client or the chair you require.

Use inches or centimetres but be consistent and communicate them very clearly to the provider. If you are using a material measure make sure that the measurements are ‘straight line’ rather than being shaped around the client as this will give you a different result.

Check that the client is wearing their usual footwear during measurement. For example, if they normally wear slippers then assessing and measuring them whilst wearing heeled boots would make a big difference to the result.

For more information about measurement see pages 14 and 15 of our Clinical Posture Guide which also contains a wealth of other information on client assessment.  If the person you are measuring is Plus Sized Posture Guide leaflet.


Width (A)

Measure the width of the bottom in a seated position so that you take into account any spread. An inch (2.5cm) should then be added to this measurement to indicate the appropriate seat width requirement. This is to ensure that the skin is not compromised by repeated friction during sitting or standing transfer.

Depth (B)

Ensure that the measurement is taken from the rear most point of the bottom to the Popliteal Fossa and that the client’s bottom is as far back in the chair as possible. Typically the chair needs to be an inch less than this measurement to support good posture, but this depends on body shape. As a general rule there should be space here to place 2 fingers between the back of the knee and the chair.

Height (C)

Measure from the floor to the Popliteal Fossa. This measurement is critical as it supports the pelvic angle. The thighs should be horizontal to the seat base and at no point should the knees be higher than the pelvis.

Lumbar support (D)

Firstly, it is important to determine whether there is a spinal abnormality that is fixed or flexible. If flexible or partly correctable you may be able to alter the posture using features of the chair’s additional postural support systems. This will support better long-term posture and minimise deterioration in function and/or skin integrity. In a normal spine a lumbar support would be measured from the seat crease behind the knee vertically to the mid-lumbar curve.

Backrest height (E)

This will depend on what the client’s support requirements are. Be clear whether the measurement is for the back (base of spine to top of the shoulders) or includes the head height.  If using a waterfall back cushion to support posture for example, it is important that the provider knows what the measurements incorporate so that they can differentiate between back and head/neck support.

Armrest height (F & G)

(F) represents the armrest height from the seat base (cushion) to the forearm when in a 90º flexed position from the humerus.

(G) represents the armrest height from the floor so that in conjunction with (F) the armrest height can be verified. In the absence of contractures or deformities (G) = (C) + (F).

Shoulder width (H)

This measurement ensures that the chair is suitably supporting the upper body, particularly if the client requires lateral support. Too much width allows the client to lean, impacting negatively on posture. The client should be well supported without being constrained.

Plus Sized Measurement

Measuring a chair correctly is critical in all cases but, made more complex when assessing for a plus sized person.   Tissue often inhibits the ability to feel or see prominences as well as the impact of weight and force of gravity which encourages problematic posture.  It may be advisable to use two people to ensure that the measurements are accurate.  Please refer to our Plus Sized Seating Review for further details.