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ost people rate comfort as the most important requirement of a chair. Style, appearance, and sturdy joinery are also undeniable key elements, but if any of these criteria results in an uncomfortable chair, the product may end up being used as little more than an attractive showpiece.
Uncomfortable chairs give rise to a familiar litany of complaints: cutting off circulation to the legs; straining neck, shoulder, and back muscles; and squeezing the legs together. Each of these problems stems from the fact that, although very few people share the same size and shape, most chair designs are inspired by the “one size Fits all” philosophy. Some chairs, like those found in fast – food restaurants for example, are actually intended to be uncomfortable to discourage users from sitting in them for lengthy periods.
The standard dimensions for various types of chairs presented in the chart
below derive from the statistical sciences of anthropometry and ergonomics, which deal with measuring human bodies and tailoring what is made to the human form. The measurements provide good starting points for designing chairs, but following these guidelines slavishly will yield pieces that are only well suited for people of average build. Standard-size chairs can be uncomfortable for individuals who do not fit the mold: children; pregnant women; or people who are taller, shorter, or heavier than the average. But as a woodworker, you have the opportunity to fine-tune the design of your chairs to fit the individual user.
There are a few basic principles to follow. Seats that slope back slightly, for example, help position body weight more comfortably. Positioning a seat so that the user’s feet will be firmly planted on the floor will not cut off circulation to the legs. Armrests that are properly
located will minimize muscle tension in the shoulders. If the whole chair is to be angled back, the seat must also tilt backward to keep the user from sliding forward and prevent the front of the seat from cutting off circulation to the legs.
Well-designed backrests that conform to the shape of the human spine are crucial. For instance, a backrest should be concave to wrap around the back of the rib cage, shoulders, and waist. It should also curve from bottom to top, rather than be made perfectly straight, in order to support the vertebrae forming the reverse curve of the spinal column. Whatever its style, function, or design, a chair must support the lower five vertebrae in the small of the back, known as the lumbar region. And for a reclining chair, which places the head behind the center of gravity, the backrest must be high enough to also support the spine’s upper section, known as the dorsal region.
STANDARD CHAIR DIMENSIONS
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CUSTOM-FITTING A CHAIR
Like a tailored suit, a custom-built chair should be made to follow the contours of a particular user’s body. To design such a chair, have the person sit upright on a flat bench and take the measurements listed at right. Using your measurements along with the anatomy illustration shown above and the standard dimensions in the chart on page 14, you can make a mockup chair from a light material like corrugated cardboard, laminated to whatever thickness of stock you need with thinned white glue. This mockup can help you design the chair and make the templates you will need to size its parts.
• For seat width, measure across the hips.
• For seat height, measure from the floor to the underside of the user’s knee.
• For maximum seat depth, measure from the crook of the knee to the lower back.
• For arm rest height, measure from the seat to the elbow.
• To determine where lumbar support is needed, measure from the seat to the waist.
• For minimum backrest height for a dining chair, measure from the seat to the armpit.
