Fifteen and a Half Inches
An inch.
Maya Lin measures fourteen and a half inches across the hips.
Her seat width is fifteen and a half.
The chair my son bought was eighteen.
And here is why that is not a quibble, and here is the sentence from Debra Ngwenya that I have repeated to perhaps two hundred people.
“The width of the seat decides where her hands go.”
On a chair that is too wide, your shoulders have to abduct — go out sideways — to reach the hand-rims.