# Is there a procedure or equation to calculate optimal height of a seat based on a given person?

I have a really bad back, and I find that sitting on hard surfaces is preferable to soft surfaces. I'd like to figure out what the optimal height is for a seat for me so that I am not cutting off circulation by having my legs dangle, or exacerbating the bad back condition by having my feet too positively engaged to the floor.

Is there a commonly accepted wisdom with regards to seating height? Is there a universal standard or is it something that can be calculated based on the situation? I would assume the ergonomics of a person varies by that person.

• The best advice I've seen is to build mockups out of plywood and scrap and rebuild them until they fit your body... or, as with the fancy ergo office chairs, make the chair itself highly adjustable. Commented Jun 3, 2015 at 14:17
• I know this doesn't help you with your design, but on a few occasions I've switched to a folding chair when my office chair was bugging me.
– rob
Commented Jun 3, 2015 at 17:53
• I have an Aeron here at my desk which is supposed to be the pinnacle of back pain comfort. It's not too bad, but some of the other chairs in the house downstairs aren't quite so comfortable, so I was thinking of making a simple bench. I just wanted to figure out optimal height for comfort. Commented Jun 4, 2015 at 13:06

As TX Turner said there may not be a particularly good formula for coming up with that height, but this should work as a procedure:

• Take an old chair and make a back rest adjuster to bring you to the same back angle of the new chair.
• Cut the legs off shorter than you think you'll need
• Fortunately, it's easy to make them shorter if needed
• Cut a stack of plywood squares just larger than the base of the chair
• Put a couple of pieces of plywood under the legs and sit down* **
• if the chair is too low, add another piece of plywood
• if the chair is too high, take one out.

*Use care when sitting because the chair could slide off the plywood.
**Different thicknesses of plywood will make the fitting process quicker (thick pieces) and more accurate (thin pieces).

This is similar to getting a custom bike fitting where they use a purpose-designed, very adjustable bike frame to get exact measurements to either set up a factory-built bike or build a custom frame. One style looks like this:

(source: next-fit.com)
Image linked from R + E Cycles

There is a book by Jeff Miller on chair design cleverly named Chairmaking & Design which is chock full of information on chair design and issues regarding wood, such as shrinkage and joint construction. One of his projects is to make an adjustable jig that holds dowels horizontally, so different shaped profiles can be tried and tested very quickly. When you find a shape you like, you can construct something similar that is more permanent. The rest of the book is a good read as well, with many other design approaches.

On the other end of the spectrum is anthropometrics and ergonomics, which contain a wealth of data but are not aimed at woodworkers. This example is short and readable and may lead to more interesting reading: http://www.allsteeloffice.com/SynergyDocuments/ErgonomicsAndDesignReferenceGuideWhitePaper.pdf

The field of ergonomics is filled with opinions, which leads to some weird chair designs- remember this?

or..

Or..

That being said, there are some actually good ergonomic chairs, but I've seen wildly different results with different people and the same chair. I'm not sure that the science of ergonomics is advanced enough to synthesize a rule that applies to more than a subset of people at once.

• Could you please give credit to the obstetrics supply catalog you got those images from? =)
– null
Commented Jun 3, 2015 at 21:01