I heard a landscape designer say this yesterday on an HGTV television program.

Problem:
This is a mispronunciation of a noun for one of the three basic dimensions.

Explanation:
The endings of the nouns for the other two basic dimensions seem to interfere with how some speakers pronounce “height”.

The nouns “length” and “width” end with the “th” sound that begins the word “thin”, so it seems that some speakers want to pronounce “height” with this “th” sound, too.

Wondering whether this speech problem also occurred in writing on the Web, I searched Google for “heighth” and “height” and got about 112,000 and 42,500,000 matches, respectively. That tells me that Web authors have written the word correctly by a ratio of 379.5:1, which is excellent. And, because the most popular “heighth” matches on Google talk about why this is a misspelling of “height”, the ratio of correct use to incorrect use probably is much higher.

Solution:
“Height”