Must-have measurements for comfortable seating
Thinking about designing a chair but struggling with determining the dimensions and angles that will guarantee maximum comfort? Then let us introduce you to the guidelines established by the furniture industries. Keep in mind that they apply to an average-size 5' 10" adult sitting in an upright position. You may need to adjust the dimensions and angles slightly depending on the intended user's size and shape.
Also, to help with your visual understanding of chair design, we letter-keyed the guidelines for the seat, back, and armrest dimensions and angles to the drawings above and right. Now, try them out for a chair that looks right and feels great.
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 (1–11⁄2 " 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, and K .Make armrests a minimum of 8" long, 2" wide, and spaced approximately 19" apart.