Changing distance between titles and page numbers and alignment using tocloft

Question

I am trying to produce a TOC that runs ragged right. I want the distance between all titles (parts, chapters, sections) and page numbers to be 3 times the distance that's between the part/chapter/section number and the title. No dots or anything.

I see how to set the indentation from the right by changing 4em in the MWE below, but I do not know how to calculate the appropriate number.

I would also like to align the front matter/intro title with the part number below it and then both of those aligned with the chapter titles instead of everything flush left.

\documentclass{book}

\usepackage[titles]{tocloft}

\renewcommand{\cftdotsep}{\cftnodots}
\renewcommand{\cftpartafterpnum}{\hspace*{4em}}
\renewcommand{\cftchapafterpnum}{\hspace*{4em}}
\renewcommand{\cftsecafterpnum}{\hspace*{4em}}
\renewcommand{\cftpnumalign}{l}

\begin{document}

\frontmatter
\tableofcontents
\chapter{Introduction}
\part{This is Part One}
\mainmatter
\chapter{First Chapter}
\section{First Section}

\end{document}

So the I from Introduction should be aligned with the I which is the part number, and these both should be indented to align with the F from First Chapter.

Suggestions?

Answer 1

Try this:

% tocprob.tex  SE 552100

\documentclass{book}
\usepackage[titles]{tocloft}

%%%%%% your code
\renewcommand{\cftdotsep}{\cftnodots}
\renewcommand{\cftpartafterpnum}{\hspace*{4em}}
\renewcommand{\cftchapafterpnum}{\hspace*{4em}}
\renewcommand{\cftsecafterpnum}{\hspace*{4em}}
\renewcommand{\cftpnumalign}{l}

%%%%%%%%% my code
\newlength{\mylength}
\setlength{\mylength}{10em}
\renewcommand{\cftpartafterpnum}{\cftparfillskip}
\renewcommand{\cftchapafterpnum}{\cftparfillskip}
\renewcommand{\cftsecafterpnum}{\cftparfillskip}
\renewcommand{\cftpartpagefont}{\hspace{\mylength}\large\bfseries}
\renewcommand{\cftchappagefont}{\hspace{\mylength}\bfseries}
\renewcommand{\cftsecpagefont}{\hspace{\mylength}\normalfont}
\renewcommand{\cftpartleader}{}
\renewcommand{\cftchapleader}{}
\renewcommand{\cftsecleader}{}

\setlength{\cftpartindent}{1.2em} % align part numbers with chapter titles 

\begin{document}

\frontmatter
\setlength{\cftchapindent}{3em} % indent unnumbered chapters
\tableofcontents
\chapter{Introduction}
\part{This is Part One}
\addtocontents{toc}{\setlength{\cftchapindent}{2em}} % regular chapter indent
\mainmatter
\chapter{First Chapter}
\section{First Section}

\end{document}

I used a spacing of \mylength between the end of the titles and the page numbers. The actual space between a number and the title text is specified by the \cftXnumwidth tocloft macros which by default are different for each X (> texdoc tocloft). You could use a multiple of these for each division level but I'm not sure that it would enhance the viewer's impression.

I have edited my original answer to try and cater for the questioner's comments.