Confusion: \onehalfspacing vs. \spacing vs. Word vs. the world?

Question

I have to write a paper with the requirement to use "1.5 line spacing" 12pt Times New Roman. Naturally I used

\usepackage{setspace}
\begin{document}
\onehalfspacing
Lorem ipsum…

So far so good. But I'm a litte paranoid so I checked it with Word and was suprised to get something completely different, so I made this comparison:

you may have to open that in a new tab.

But seriously? Am I missing something? Everyone recommends using \onehalfspacing but that can't be right? I checked the text with a bare minimum and the results are the same:

\documentclass[12pt]{article}

\usepackage[utf8]{inputenc}
\usepackage{mathptmx}
\usepackage{setspace}

\begin{document}
\onehalfspacing
Lorem ipsum...

I guess my question is: what setting should I use?

Answer 1

Try

    \linespread{1.25}

This equals 1.5 linespacing in Word, as was corrected by the comments (Beni cherniavsky paskin).

Answer 2

Not exactly an answer but a caveat: Some of these seem sensitive to placement.
[TL;DR: all 3 affect the whole document if placed in preamble.]
I found experimentally (in a \documentclass[a4paper,11pt]{article} doc) that:

\linespread{1.213}:

• before \begin{document} affects the whole document
• between \begin{document} and \maketitle affects only the title
• after \maketitle has zero effect

\onehalfspacing (same result as above in a 11pt doc):

• as package option (\usepackage[onehalfspacing]{setspace}) affects the whole document
• before \begin{document} affects the whole document
• between \begin{document} and \maketitle affects the whole document
• after \maketitle affects the whole document except title

\spacing{1.213}:

• before \begin{document} affects the whole document
• between \begin{document} and \maketitle affects the whole document
• after \maketitle affects the whole document except title

As you found, \spacing{1.5} results in much more spacing than the first two; \spacing{1.213} results in exactly the same. So it seems \spacing uses the same units as \linespread.

CAVEAT: it seems setspace package redefines \spacing{} and I'm not sure now if I did the above tests with the package loaded or not?

I'm still confused which I should use. setspace package is certainly the more polished option — it doesn't space footnotes and captions, and as https://tex.stackexchange.com/a/30114/7262 explains it adjusts params for 10pt/11pt/12pt which would be cumbersome and easy to forget otherwise. It's also robust wrt. placement and provides clean ways to change spacing in parts of the document.

On What does 'double spacing' mean? most opinions conclude that setspace invented its own definition of 1.5 / double spacing, while Word uses what's probably the historically common definition — it there ever was one — but it might not matter as most people requiring "double spacing" don't know what it should mean and in practice accept both...

Answer 3

Microsoft Word doesn't do line spacing correctly (unless you multiply the pt value of the text yourself and use the "Exactly" line-spacing option). If you actually measure line height in a graphics-editing program—from the top of the tallest letter to the bottom of a lowest letter—\onehalfspacing uses exactly 0.5 of this height below each line.

From http://practicaltypography.com/line-spacing.html,

For most text, the op­ti­mal line spac­ing is be­tween 120% and 145% of the point size.

In Microsoft Word,

To get line spac­ing in the 120–145% range, use a Multiple value of 1.03–1.24. (Not 1.20–1.45—as noted above, Word uses pe­cu­liar line-spac­ing math.)

So to answer your question, if you want true 1.5 line spacing, go with \onehalfspacing. However, to most people, 1.5 line spacing probably means using the (incorrect) "1.5 line spacing" option in Word. It would be best to ask your lecturer for an example paper.