Chair Dimensions

I want to design my furniture so that it meets the specifications of an average adult i.e. height, width and depth so that it is comfortable to sit on. I have been searching around to get a better understanding of what the guidelines are to designing seating and I stumbled across:

Brezlin: Custom Furniture and Cabinetry:
http://www.brezlin.com/design/chairguidelines.html

Their dimensions are in imperial units however, but these will be easily converted to metric when I need to. Brezlin state:

Chair Design Guidelines

1. The occupant should be able to sit in and get up from the chair without difficulty. The feet should rest flat on the floor without the knees projecting above the upper leg. A seat height of 16 to 18 inches fits the bill for most adults. Arm rests should support the forearms without raising the shoulders (7" to 9" above seat). Half arm rests enable the chair to be drawn up close to a table.
2. The depth of the seat should allow clearance from the front edge of the seat to the back of the occupant's leg. A seat that is too deep will press against the back of the legs forcing the occupant to slouch forward. A seat that is too shallow may be unstable and feel precarious. A seat depth of 15 to 18 inches is recommended for most adults.
3. The width of the seat often tapers by 2" to 3" from the front to the rear to allow clearance for legs and clothes in front while allowing elbow room in back. Many chairs have seats that are about 15" wide in the rear and 18" wide in the front.
4. For relaxed seating, the seat should slant slightly toward the back (about 5° to 8°) to keep the occupant from slipping out of the chair. However, an office desk or typist's chair often has a flat seat to facilitate leaning forward.
5. The back of the chair is often slanted backwards for comfort - up to 5° for a dining chair and 10° to 15° for a more casual chair. As the chair back angle increases, the seat should be tilted further backward to prevent forward sliding and lowered to prevent the front edge of the seat from pressing against the back of the legs.
6. The seat back should support the lumbar region without being so high as to interfere with the shoulder blades. A back height of about 12" to 16" above the seat is ideal for most adults. Note that this guideline is often ignored for formal "high-backed" dining chairs.
7. The lower portion of the seat back (first 4"-8") should curve out or be left open to allow room for the buttocks.

Chair Dimensions For Average-Sized Adults

The following dimensions apply to chairs designed for average-sized adults sitting in an upright or alert posture.

• Seat width 16"-20"
• Seat depth 15"-18"
• Seat height from floor 16"-18"
• Slope of seat front to rear 5° to 8° (3/4" to 1" drop)
• Arm rest height above seat 7"-9"
• Arm rest length (full arm rest) 8" minimum
• Arm rest width 2" average
• Set back of arm rest from front 2"-3"
• Seat back height 12"-16" above seat
• Seat back recline angle 0°-5° (formal); 10°-15° (casual)

Wood Selection for Chairs

• Use hardwoods for pieces where shocks, abrasions, and other stresses will occur.
• Use softwoods in larger thicknesses to enable greater penetration of hardwood pieces (e.g., spindles).
• Do not join softwood to softwood.
• For bent chair parts, select woods such as white oak or ash that can be steam-bent without fracturing.
• Legs: The legs of a chair are subject to extreme stresses and abrasive forces. Select a wood such as hard maple that is hard, resists impression, and does not splinter.
• Stretchers: Abrasion resistance is less of an issue but a hard wood such as maple is recommended. Bending strength may be important (e.g., feet placed on the stretcher), so consider white oak or hickory.
• Seat: Many woods will suffice, but soft woods such as pine or poplar are much easier to sculpt if you are intending to use hand tools (early craftsmen typically chose soft woods for this reason).
• Back: Use hard woods such as maple, oak or ash for spindles. For longer spindles, select a resilient wood that allows for movement - hickory is ideal.
• Softwoods in thicker dimensions may be used for arms and rails.