Space between figure caption and bottom margin

Question

I am looking to put a figure at the bottom of my document in a way that the caption is aligned with the bottom margin (i.e. no space between text and margin). Here's a MWE:

\documentclass[12pt]{report}
\usepackage[top=1.0in,hmargin=1.25in,height=9.0in,letterpaper,showframe]{geometry}
\usepackage[document]{ragged2e}
\usepackage{setspace}
\usepackage{graphicx}
\usepackage[labelfont=bf,justification=RaggedRight,singlelinecheck=off,%
           labelsep=period]{caption}
\usepackage{duckuments}
\usepackage{blindtext}

\begin{document}
\RaggedRight    
\doublespace
\chapter{Title of chapter}
\blindtext  
\begin{figure}[b]
    \centering
    \includegraphics[height=3cm]{example-image-duck}
    \caption{This is a caption that is very long for the figure and it should be aligned with the bottom margin}
\end{figure}
\blindtext
\blindtext
\begin{figure}[t]
    \centering
    \includegraphics[height=3cm]{example-image-duck}
    \caption{This is the caption.}
\end{figure}    
\end{document}

The first figure is set at the bottom, but the caption doesn't align with the margin (there is a space between the text and the margin). The one aligned at the top, however, does align to the margin, so I didn't want to mess with the padding the figure environment has.

Edit:

Here's a screenshot, I drew the redline (on an editor) to indicate the spacing I am talking about.

Answer 1

You can use \flushbottom to get always the last line of a page aligned with the bottom of typing area.

Please see the code:

\documentclass[12pt]{report}

\usepackage[top=1.0in,hmargin=1.25in,height=9.0in,letterpaper,showframe]{geometry}
\usepackage[document]{ragged2e}
\usepackage{setspace}
\usepackage{graphicx}
\usepackage[%
  labelfont=bf,
  justification=RaggedRight,
  singlelinecheck=off,%
  labelsep=period
]{caption}

\usepackage{duckuments}
\usepackage{blindtext}


\begin{document}
\flushbottom % <========================================================
\RaggedRight
\doublespace
\chapter{Title of chapter}
\blindtext
\begin{figure}[b]
  \centering
  \includegraphics[height=3cm]{example-image-duck}
  \caption{This is a caption that is very long for the figure and it should be aligned with the bottom margin}
\end{figure}
\blindtext
\blindtext
\begin{figure}[t]
    \centering
    \includegraphics[height=3cm]{example-image-duck}
    \caption{This is the caption.}
\end{figure}
\end{document}

and the result:

Answer 2

It seems that when the text is stretched to fit the page, the bottom float is pulled up. So by letting \textfloatsep expand instead, one can prevent that from happening. All that is left is to remove the space below the baseline of the caption.

\documentclass[12pt]{report}
\usepackage[top=1.0in,hmargin=1.25in,height=9.0in,letterpaper,showframe]{geometry}
\usepackage[document]{ragged2e}
\usepackage{setspace}
\usepackage{graphicx}
\usepackage[labelfont=bf,justification=RaggedRight,singlelinecheck=off,%
           labelsep=period]{caption}
\usepackage{duckuments}
\usepackage{blindtext}

\addtolength{\textfloatsep}{0pt plus 0.01fil}

\begin{document}
\RaggedRight    
\doublespace
\chapter{Title of chapter}
\blindtext  
\begin{figure}[b]
    \hrule
    \centering
    \includegraphics[height=3cm]{example-image-duck}
    \caption{This is a caption that is very long for the figure and it should be aligned with the bottom margin}
    \vskip-\dp\strutbox%\hrule
\end{figure}
\blindtext
\blindtext
\begin{figure}[t]
    \centering
    \includegraphics[height=3cm]{example-image-duck}
    \caption{This is the caption.}
\end{figure}    
\end{document}