# 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.

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Perhaps not an exact duplicate, but surely of interest: tex.stackexchange.com/questions/13742/… – lockstep Sep 30 '11 at 15:41
There's no official definition of "double spaced". Pick what is less displeasing ("more pleasing" would be an oxymoron). – egreg Sep 30 '11 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. – Leo Liu Sep 30 '11 at 15:51
I like curiosity questions. There should be an extra tag for it :) – topskip Sep 30 '11 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.

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Extending lockstep's answer to other documentclass 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.

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