# Why is the linespread factor as it is?

The blog post Quick note on line spacing discusses line spacing and it says

To change the line spacing for the entire document, you can use the `linespread` command in your preamble:

``````\linespread{<factor>}
``````

The factor is somewhat confusing. For double-spacing you have to use 1.6 and for one-and-a-half spacing 1.3. Not very intuitive, but I'm sure there is a reason for it.

This unintuitive factor triggered my curiosity. What is the reason for it being as it is?

This question is just motivated by my curiosity and I have no practical reason for asking it. Feel free to close it if it's inappropriate or see at as post in the same vein as \nothing, \varnothing and \emptyset in that it asks about history or some design decision.

• Perhaps not an exact duplicate, but surely of interest: tex.stackexchange.com/questions/13742/… Sep 30, 2011 at 15:41
• There's no official definition of "double spaced". Pick what is less displeasing ("more pleasing" would be an oxymoron). Sep 30, 2011 at 15:44
• In my previous question, there may be 3 different definitions of "double-spacing". `setspace` package uses a different one other than MS Word, Ooo Write, etc. Sep 30, 2011 at 15:51
• I like curiosity questions. There should be an extra tag for it :) Sep 30, 2011 at 19:53

With the LaTeX standard classes (`article`, `book`, and `report`) and no class options added, `\normalsize` results in a font size (size of the largest glyphs in a font -- typically, braces) of `10pt` and a `\baselineskip` (vertical skip between the base lines of two successive lines of type) of `12pt`. The ratio between font size and `\baselineskip` is 1.2.

The `linespread` command (which must be issued in the document preamble) may be used to change the `\baselineskip` without changing the font size.

A possible definition of `\onehalfspacing` and `\doublespacing` is that the ratio between font size and `\baselineskip` should be 1.5 resp. 2. Because the "basic" ratio for `10pt` is 1.2, a multiplier of 1.25 and (approximately) 1.667 has to be applied -- and this is basically what the `setspace` package does. ("Basically" because it retains the ratio of 1.2 for footnotes and the like.)

The statement "For double-spacing you have to use 1.6 and for one-and-a-half spacing 1.3" amounts to either a rounding error, or being confused, or both.

• If `\linespread` is a command for changing `\baselineskip`, wouldn't it be easier to just change `\baselineskip`? Oct 6, 2017 at 12:34
• @Sverre No`\linespread` does not change (immediately) `\baselineskip`. What it does is to modify the `\baselinestretch` which impacts size changing commands or font selection comand (which are the ones which will change the `\baselineskip` and other things). Thus the `\linespread` effects persists across font size changes.
– user4686
Jun 3, 2018 at 8:44

Extending lockstep's answer to other document class options (like `11pt` and `12pt`) gives rise to the seemingly strange scaling factors used by the `setspace` package:

• `10pt` (already discussed)

`setspace` defines the scaling factor to be `1.25` for `\onehalfspacing` and `1.667` for `\doublespacing`, since the "basic" ratio is `1.2` (`\normalfont` has a `\baselineskip` of `12pt`; see `size10.clo`)

• `11pt`

`setspace` defines the scaling factor to be `1.213` for `\onehalfspacing` and `1.618` for `\doublespacing`, since the "basic" ratio is `1.236` (`\normalfont` has a `\baselineskip` of `13.6pt`; see `size11.clo`)

• `12pt`

`setspace` defines the scaling factor to be `1.241` for `\onehalfspacing` and `1.655` for `\doublespacing`, since the "basic" ratio is `1.208` (`\normalfont` has a `\baselineskip` of `14.5pt`; see `size12.clo`)

As such, in the following hypothetical situation, a scaling factor of `2.4` (that is, `\setstretch{2.4}`) would provide "triple spacing" in a document with normal font size of `16pt` and `\baselineskip` of `20pt`.

All scaling factors are rounded to 3 digits after the decimal.

I recently tried to customize the line spacing in a `ctex` document and this post served as one of my references. During my research, however, I found a mistake made by the `setspace` package.

To further extend Werner’s answer, I want to point out that `setspace` has set both factors for an `11pt` article wrong, unfortunately.

We find in `size11.clo` that `\normalsize` is defined by

``````\@setfontsize\normalsize\@xipt{13.6}%
``````

The problem is that the “basic” ratio in `11pt` article is not `13.6/11` but rather `13.6/10.95` for historical reasons. This implies that for `\onehalfspacing`, the factor should be around `1.2077205882`, not `1.213`; and for `\doublespacing`, the factor should be around `1.6102941176`, not `1.618`.

I have no idea why `article` inconsistently sets the body text leading/fontsize basic ratio to be `1.2`, `1.242` (not `1.236`) and `1.208` for `10pt`, `11pt` and `12pt`, respectively.