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. Armrests should support the forearms without raising the shoulders (7" to 9" above seat). Half armrests 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) Armrest height above seat 7"-9" Armrest length (full armrest) 8" minimum Armrest width 2" average Set back of armrest from front 2"-3" Seat back height 12"-16" above seat Seat back recline angle 0°-5° (formal); 10°-15° (casual) Chair Dimensions for Children The following table presents seat heights for children of various ages. Other chair dimensions can be derived proportionately based on the chair dimensions for adults. For most elementary school age children, a seat width and depth of 12 to 14 inches, a backrest height of 9 to 11 inches, and an armrest height of 5 to 7 inches are good starting points. Child's Age (Years) Seat Height 1 to 4 10"-12" 5 to 7 12"-14" 8 to 10 13"-17" 11 to 13 15"-18" Specifications for Different Types of Seats (Listed dimensions are based on average-sized adults). Dining Chair: The seat height averages 16" to 17", seat width averages about 15-1/2" in back and 18" in front, and average seat depth is 16" to 16-1/2". If armrests are used, they should be 7" to 9" above the seat but able to fit under the table apron. The average width between armrests at the front of the chair is approximately 19". The seat is usually level or has a maximum front to back slope of about 1". The seat back is reclined no more than 5 degrees and ranges in height from 12" to 20" above the seat (or higher in very formal chairs). Desk Chair: Most specifications for a dining chair apply here except that the seat back often protrudes no higher than the middle of the back - about 14" to 16". Easy Chair: Should provide a more relaxed, reclining position than a dining chair - seat height is lower (about 16") with allowance made for compression of seat cushion. The seat is angled backwards about 10 degrees with a seat to back angle of 95 to 120 degrees. For maximum comfort, the seat back should be no more than 14" to 16" above the seat. Armrests are recommended for easy in/out and they average 5" to 8" in height and 2" to 4" in width. Sofa/Loveseat: Seat depth ranges from 18" to 22" and seat height ranges from 14" to 18" (16" average). The seat back typically rises 15" to 18" above the seat and is usually angled backwards at up to 25 degrees. Upholstered seats generally slope 1" from front to back. Armrests generally protrude 4" to 8" above seat. The overall width of a loveseat is about 56" to 60" - 24" per person, plus 4" to 6" for each armrest. A full-size sofa measures about 90" in overall width. Bar Stool: In general, the seat of a bar stool should be 12" to 15" below the top surface of the bar, but never higher than 30". For a normal bar that is 40" to 45" high, a seat height of 28" to 30" is standard. For a 30" high bar (most tables), a seat height of 22" to 24" is standard. The seat back is typically 10" to 14" above the seat. The seat width ranges from 15" to 18" and the seat depth ranges from 12" to 16" (16" to 17" diameter if the seat is round). A rung 20" below the seat provides a comfortable resting spot for the occupant's feet. Rocker: In a stationary position, the seat back should tilt back approximately 25 degrees from the vertical with a seat to seat back angle of about 95 degrees. The seat height in front should be no higher than 16" to 17". Standard seat widths and depths are 18" to 22" and 16" to 18" respectively. The seat back is higher than most chairs - about 40" above the floor. The runners commonly have a horizontal extension of about 30" with a curvature radius of 36" to 38". 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.
