The Answer is Resounding: Why Size is Non-Negotiable
A correctly sized riser chair ensures that the user maintains the optimum seated posture, often referred to as the 90-90-90 rule (90-degree angles at the ankles, knees, and hips). Deviations from this rule place unnecessary strain on the body.
Health and Postural Risks of an Incorrect Fit
Incorrect Dimension: Seat Height Too High
Health and Safety Impact: Feet dangle; weight is unevenly distributed through the buttocks and thighs, risking pressure sores and reducing standing safety.
Incorrect Dimension: Seat Depth Too Deep
Health and Safety Impact: Pressure behind the knee crease restricts blood flow; user is encouraged to slouch forward, losing back support.
Incorrect Dimension: Seat Width Too Wide
Health and Safety Impact: User tends to lean or slump to one side, compromising spinal alignment and the chair's lateral support.
Incorrect Dimension: Seat Width Too Narrow
Health and Safety Impact: Constriction and rubbing against the hips, which can cause discomfort and pressure injury risk.
Incorrect Dimension: Backrest Too Low
Health and Safety Impact: Insufficient neck and head support, leading to tension and poor posture when reclining.
The Five Critical Dimensions for a Perfect Fit
When selecting a riser chair, the internal dimensions—those which interact directly with the user’s body—are far more important than the chair’s overall width or depth in the room.
Seat Height: The Foundation of Standing Safety
The seat height is the distance from the floor to the top of the seat cushion.
How it Should Fit: When sitting with your bottom firmly against the backrest, your feet should be planted completely flat on the floor, and your knees should form a right angle (90°).
Why it Matters: The correct height makes standing up easier, as it positions your centre of gravity correctly. If the seat is too low, you lose the leverage needed to stand; if it is too high, the rising function becomes unsafe as your feet cannot gain purchase.
Seat Depth: Protecting Circulation and Posture
Seat depth is the distance from the backrest to the front edge of the seat cushion.
How it Should Fit: Your thighs should be fully supported, but you must be able to comfortably fit two fingers between the front edge of the seat and the back of your knee crease.
Why it Matters: This gap is essential to prevent pressure on the main arteries and nerves that run behind the knee. Too little depth causes the user to perch on the edge of the seat, losing essential lumbar support.
Seat Width: Balancing Comfort and Lateral Support
Seat width is the distance between the inside of the armrests.
How it Should Fit: The seat should be wide enough for comfort (typically an inch or two wider than your hips while seated) but narrow enough that you can easily and naturally rest both forearms on the armrests without leaning.
Why it Matters: The armrests provide crucial side (lateral) support. If the seat is too wide, the user has to stretch their arms out, causing shoulder tension and the loss of side support that prevents slumping.
Backrest and Head Support: Securing the Spine
This refers to the height of the backrest from the seat cushion up to the top of the headrest.
How it Should Fit: The backrest must support your entire spine and, ideally, the back of your head when you are sitting fully back.
Why it Matters: When the chair is reclined, your head and neck must be supported to avoid muscle strain. For users who intend to nap or sleep in the chair, proper head support is non-negotiable.
Armrest Height: Aiding Entry and Exit
How it Should Fit: When sitting, your forearms should rest naturally on the armrests with your shoulders in a neutral, relaxed position.
Why it Matters: The armrests are the primary point of contact for assisting with standing and sitting. If they are too low, they cannot be used effectively to push up; if they are too high, they push the shoulders into a painful, hunched position.
Matching the Chair to the User: Beyond Standard Sizes
Due to the critical nature of the five dimensions, a single "Standard" size simply cannot cater to everyone. Reputable UK manufacturers offer a range of sizes to suit different body types.
The Range of Options
Petite: Designed for shorter individuals, featuring a lower seat height and shallower seat depth.
Standard: Suits the average-sized person, with dimensions that fall within the most common range.
Grande or Large: Provides greater width and depth for taller and larger users.
Bariatric: These chairs feature reinforced frames and motors to safely accommodate higher user weights, often exceeding 25 stone (159 kg), ensuring the motor mechanism does not fail under strain.
Made-to-Measure vs. Off-the-Shelf
While many people fit one of the off-the-shelf sizes, those who are particularly tall, small, or have unique postural requirements often benefit from a made-to-measure chair. Although this process takes longer and requires precise measurements, it guarantees a truly bespoke fit that optimises therapeutic benefits and long-term comfort.
Fitting the Chair to the Home: The Room Check
In addition to fitting the user, the chair must fit the home's practical dimensions.
Overall Footprint
Always measure the chair’s total width and depth. Some large chairs may not fit through standard UK doorways or corridors.
Recline Space
The chair will require significant clear space behind it to recline fully. If space is limited, ask about a Wallhugger or Near-to-Wall mechanism, which profiles the seat forward as it reclines backward, requiring less space behind the chair (sometimes as little as 15 centimetres). Failure to account for this can prevent the chair from achieving the vital therapeutic recline positions.