pgfplots: Two Y-axes in different unit systems

Question

I am attempting to create a graph showing some results, and to plot SI units on the left Y-axis and Imperial units on the right y-axis. My MWE so far is getting close, but as you can see from the screenshot the right Y-axis is not scaled properly nor is it in the correct location. What am I missing for the right Y-axis to get this displayed properly?

\documentclass[letterpaper]{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16}
\begin{document}
\begin{figure}
    \begin{center}
        \begin{tikzpicture}
            \begin{axis}[%
                width=\linewidth,
                xmin=0, xmax=200,
                ymin=0, ymax=500,
                domain=2:200,
                range=0:700,
                samples=101,
                axis y line=left,
                restrict y to domain =0:700,
                yticklabel style={
                    /pgf/number format/fixed,
                    /pgf/number format/precision=0
                },
                scaled y ticks=false,
                xlabel={Dimension Ratio $DR$},
                ylabel={Allowable Pressure (kPa)},
                every axis plot/.append style={ultra thick},
                legend pos=south west
                ]
                %
                \addplot[
                    smooth,
                    color=black,
                    ]
                    plot {0.05/0.1(2205000/(3(x-1)^3)+0.0610.40)1000};
                    \addlegendentry{$E' = 0.40$ MPa}
                    %
            \end{axis}
            \begin{axis}[
                axis y line*=right,
                axis x line=none,
                xmin=0, xmax=1,
                ymin=0, ymax=10442.72,
                ylabel={Allowable Pressure (psf)},
                yticklabel style={
                    /pgf/number format/fixed,
                    /pgf/number format/precision=0
                },
                scaled y ticks=false,
            ]
            \end{axis}
        \end{tikzpicture}
    \end{center}
    \caption{Allowable Pressure}
\end{figure}
\end{document}

Unrelated: \addplot [..] plot {...}; -> \addplot [..] {...};, you don't need the plot keyword there. — Torbjørn T., Oct 06 '20 at 19:53
@Torbjørn T., thanks, that definitely fixed the size and position, but now the right Y-axis is jammed into the right margin. Any ideas on how to fix that besides setting the width as something less than \linewidth? — grfrazee, Oct 06 '20 at 20:01
Not really, no. You can of course put the whole tikzpicture in a resizebox, but that will of course resize the text as well. — Torbjørn T., Oct 06 '20 at 20:11
@Torbjørn T., ok, if you want to write this up an an answer, I'll accept it so you get the credit :) — grfrazee, Oct 06 '20 at 22:20
See "4.9.11 Two Ordinates (y-axis) or Multiple Axes" in the pgfplots-manual too. — cis, Oct 06 '20 at 23:39

score 2 · Accepted Answer · answered Oct 07 '20 at 14:16

The two axes must have the same size. You've changed the size of only one of them with width=\linewidth, so add the same for the other axis.

Other comments:

If there are multiple settings that are common between the two axes, you can make a style with e.g.
```
\pgfplotsset{myaxis/.style={width=0.9\linewidth, <other settings>}}
```
and then use
```
\begin{axis}[myaxis, ..
```
The plot keyword you used in \addplot [...] plot {..}; is unnecessary (and makes kind of a mix between the plain TikZ \draw plot and the pgfplots \addplot), I'd use just \addplot [...] {..};.
In general use \centering instead of the center environment inside floats, see Should I use center or centering for figures and tables?

pgfplots: Two Y-axes in different unit systems

1 Answers1