To find the comfort level of a chair is virtually impossible without actually sitting in it. Attempting to meet all variables and possible conditions for the billions of human configurations that exist can be challenging. However, once you've determined the end user then specifications should be based on the skeletal make up. I've decided that my chair will be constructed for an average size adult, however, some components will be slightly larger to exaggerate special features of the design. There are established formulas / criteria that have been predetermined by chair experts that designers can follow to ensure that the intended user will find some degree of comfort based on the human's skeletal system. In my research I've found that based on the average adult I should consider the following when dimensioning my chair for comfort:
"
First,
the seat
A)
For the occupant's feet to rest flat on the floor with a knee angle of 90–100°,
locate the seat 16–18" above the floor. If the chair will have a cushion,
account for its compressed thickness in the seat height by subtracting half the
cushion's thickness.
B)
To allow clearance between the seat's front edge and the occupant's legs, make
the seat 15–18" deep.
C)
Aim for a seat width of 16–20". Depending on the chair's style and your
preference, you can taper the seat 2–3" from front to back (1–1-1/2"
per side). A wider front provides more leg room while a narrower back allows a
little more elbow room.
D)
For added comfort, particularly when the chair will not have a cushion, slope
the seat 5–8° from front to back. This also helps keep the occupant from
sliding forward. For an office or desk chair, though, it's best to forget the
slope as a flat seat facilitates leaning forward.
Now,
the back
E)
To give lower-back support without interfering with the shoulders, plan for a
back height of 12–16" above the seat for a casual chair and 20"
(typical) for a formal chair.
F)
Slant the back up to 5° for a formal chair and up to 15° for a casual chair.
Keep in mind, though, that as the back angle increases, you need to up the seat
angle (to maintain the seat-to-back angle between 90° and 100°) to prevent
forward sliding and lower the seat height to keep the front edge of the seat
from contacting the back of the legs.
G)
To give "rear" clearance for hind parts, leave 3" of open space
between the top of the seat and bottom of the lower backrest, or curve out the
lower 4–8" of the backrest.
Finally,
the armrests
H)
For the armrests to support the forearms without elevating the shoulders,
position them 7–9" above the seat. Be sure to check the table-apron height
when determining the armrest height so the arms will slide under the apron.
I,
J, K) Make armrests a minimum of 8" long, 2" wide, and spaced
approximately 19" apart."
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