What is the point size for 1.5 leading for 11pt?

I set 11 point type in Microsoft Word using single line spacing and 1.5 line spacing, then exported to PDF and opened in Illustrator. Each line of text is a separate point-type object so it’s easy to measure the leading.

First of all, when I opened the PDF in Illustrator the point size was 10.8, not 11. Also the text was in the wrong font and complete gibberish. That’s why I never use Microsoft Word without a loaded gun to my head. So I scaled the document to make the text 11 point then measured the leading.

At single line spacing, 11 point text had 13.69 point leading, or 125%. InDesign’s default for Auto leading is 120%. At 1.5 line spacing 11 point text had 20.12 point leading, or 183%, which is a little less than 187.5% (1.5 × 125%).

So if you are trying to simulate Microsoft Word’s line spacing, I guess that’s the way to go. But why? You’re not using a word processor, you’re using something much better. Leave behind your old ideas of line spacing.

Edit: As a comparison I tried the same experiment in Pages. The text was readable, in the right font, and the right point size. 11 point text with single line spacing had 12 point leading. at 1.5 line spacing the leading was 18 point, which is 1.5 times 12. It goes to show you that single line spacing or 1.5 line spacing doesn’t mean much when different programs use different values.

I experimented and the nearest seems to be in InDesign 11pt Font with 19pt leading, but I don't know why!