Why is my spine too narrow for text?

Spine width comes straight from your page count, and a short book simply has a narrow spine. Printers set a minimum page count before they'll allow any text on the spine — for KDP that's around 80 pages for paperback (Ingram's threshold is higher). Under that, the spine is too thin to print text reliably without it wrapping onto the front or back.

If your spine text won't fit or the tool won't place it:

• Check your page count is correct — if it's lower than reality, your spine is thinner than it should be.
• If the book is genuinely thin, leave the spine blank (very common for slim books) or use only a tiny type size if the printer allows it.
• Adding front/back matter or choosing thicker (cream) paper raises the page count and widens the spine a little, if you're close to the threshold.