what is the correct height for a pillow so the neck doesn't hurt?

Hi birkett7,

Thank you for your question! 

The General Medical Officer Manual at Virtual Naval Hospital
(http://www.vnh.org/GMO/ClinicalSection/55Neckpain.html) emphasizes
the importance of selecting the proper pillow.

"Proper pillow selection and use are very helpful since large or firm
pillows force neck flexion and increase pain," the manual reads. "A
soft pillow filling the "hollow" of the neck is beneficial. A pillow
pulled into position when turning onto the side may help avoid painful
and unprotected lateral neck bending."

An article at "Health Common Sense" titled "Sound Sleep and Fresh
Life" offers more specific guidelines for pillow thickness:

"A good pillow must maintain 6~8cm height when it is pressed by the
head. Also, it is recommended to provide the neck and the shoulders
with even height. Therefore, the pillow should be put between the neck
and shoulders. It should be wider than the span between shoulders,
too." (http://litex.biz/m5/m5_07.htm)

The most helpful reference for your purposes will likely be the chart
found at the Luxurious Isotonic Pillows site
(http://www.homeenv.com/Iso_Pillow.asp). It's a commercial site but
provides a detailed chart by which to determine your optimal pillow
thickness based on your weight and height.

The Tempur Pedic Pillow site (http://www.relaxetc.com/tempedpil.html)
provides these general pillow selection recommendations for proper
body alignment according to height:

Pillow Size - - - - Height
Small---------- Up to 5'3" or who prefer a thin pillow
Medium--------5'4" to 5'11"
Large---------- 5'4" to 6' or who prefer a thick pillow

Small = 20x12x3
Medium = 20x12x4
Large = 20x12x4.5

I used the following search strings to find your answer:
"proper pillow selection"
"recommended pillow thickness"
"recommended pillow height"

All the best!

Emjay-ga