Est. 1998 — 27 years of woodworking knowledge
Chair seat height question
Barry Irby
I asked this in the thread below but I thought I would sort it out and ask it on it's own.
For a chair I normally make the seat 18" off the floor. the chairs I am working on will have padded seats. So, what thickness of foam do you use? Is there a density rating? and do you take the foam into account? Like maybe the top of the foam is 19" off the floor and when you sit on it it compresses?
Let your tush be the judge
Re: Chair seat height question
Philip F Duffy
We ole folks like a higher seat as our knees don't handle the load so well any more. Push it up to 20 in at least, please. P
Re: Chair seat height question
Ellis Walentine
According to my go-to book of anthropometric data for furniture and architecture, Human Dimension and Interior Space (Panero and Zelnik, 1979), ideal seat height is based on the "popliteal height" of the sitter, which ranges between 15 1/2 - 19.3 in. for men and 14 - 17 1/2 in. for women, and varies also with age, with the accepted universal height usually pegged between 16 and 17 inches from the floor. Seat height is calculated at the front edge of the seat, as most seats slant backward by some amount, depending on the design of the chair/seat. These numbers represent the average popliteal heights of people at the 5th and 95th percentile of height, so if these chairs are for a particular client or family, it would be good to know if they are of average stature, or taller or shorter, and vary the height accordingly.
Other things to consider are the table height (typically 29 - 30 in.) and the space between the seat and the apron rail of the table (minimum 7 1/2 in.). For taller tables, I'd increase the seat height, with the understanding that if seat height exceeds the popliteal height of the sitter, it will result in more pressure and possible discomfort at the back of the thigh. You don't want the legs of shorter diners falling asleep because you've designed the chairs for taller diners. 
Foam "durometer" is a relative measurement of the hardness or compressibility of an elastic material such as foam rubber and has no absolute value. The important thing for you to know when designing with foam rubber -- especially in a seat-height calculation -- is what the actual compression will be when your customer sits on the chair, and even that isn't going to be a vital consideration, as there is no ideal seat height that fits everyone.
Ain't furniture design grand?
Ellis
Re: Chair seat height question
Philip F Duffy
It would be interesting to know the publication date of your reference since the size of the average American has grown significantly over the past 100 years. Consequently the height of the chair may have to be adjusted accordingly. P.
Re: Chair seat height question
David Weaver
CDC did a comparison of average height 2012 vs. 1912 (curious to me as I'm right around the current average in height and have often heard claims of average heights for males of 5'2" or something 100 years ago).
Male heights (Adults) are up slightly over 1.5" over 100 years (average height, not median), and female heights are up about 0.5".
https://ahundredyearsago.com/2012/02/06/average-height-for-males-and-females-in-1912-and-2012/
more interesting is the disparity in child height - it's greater and then the gap closes at later ages (underfed children?).
proportional chair height increase would be about 1/2 inch.
The aged population is probably significantly higher in proportion now, though, too, so maybe a little more.
Re: Chair seat height question
Jesse Cloud
And to make it even more complicated, most of us lose some height as we age.
Re: Chair seat height question
Paul Leuba
It appears that we need a design for a chair with adjustable leg lengths.
Paul in Hunt Valley, MD
Re: Chair seat height question
Gary Focht
Based on my dining table and other tables, chair height needs to be set such that knees fit comfortably under the table aprons. Height of the person sitting in the chair is secondary.
Re: Chair seat height question
Sgian Dubh
It appears that we need a design for a chair with adjustable leg lengths.
Such chairs are quite common and available. Office chairs frequently include height adjustment on a metal leg affixed to a five footed base on castors. Of course, their versatility for use outside an office environment are probably a bit limited, ha, ha. Slainte.