Are you talking about tops to cut from??Or sewing? Either way your ergonomics would tell you to have a slight bend at your elboy while hands are on the countertops...same w/sewing. Does your kitchen countertops fit you?Are you comfortable at their height?If so, measure them.
Here's a good example of sewing machine position at:
http://www.osha.gov/SLTC/etools/sewi...iondesign.html
also, here's some info w/measurments at:
http://www.lemontreetales.com/lemon_...hen-i-sew.html at the bottom of her page is more info on sewing room ideas, etc