How to reduce table width?

Question

I'm trying to add a table to my IEEE paper but its width is too much. Please help me fix the width to make it fit.

\documentclass[conference]{IEEEtran}
\IEEEoverridecommandlockouts
\usepackage{cite}
\usepackage{amsmath,amssymb,amsfonts}
\usepackage{algorithmic}
\usepackage{graphicx}
\usepackage{float}
\usepackage{tabularx}
\usepackage{textcomp}
\usepackage{xcolor}
\def\BibTeX{{\rm B\kern-.05em{\sc i\kern-.025em b}\kern-.08em
    T\kern-.1667em\lower.7ex\hbox{E}\kern-.125emX}}
\begin{document}
.
.
.
.
\begin{table}[h!]
    \centering
    \begin{tabularx}{0.3\textwidth}{|c c c c c c|} 
     \hline
     Feature 1 & Feature 2 & Accuracy & Precision & Recall & Specificity \ [0.5ex] 
     \hline\hline
     original dna size & compressed dna size & 0.999 & 0.999 & 0.999 & 0.999 \
     \hline
     original dna size & compression ratio & 0.999 & 0.999 & 0.999 & 0.999 \ [1ex] 
     \hline
    \end{tabularx}
    \caption{caption}
    \label{tab:my_label}
\end{table}
.
.
.
.
\end{document}

Answer 1

Edit: I delete my first version of answer since was based on @Skillmon comments which he later converted in excellent answer (+1). So I decide first to delete mine.

But now renew it with an example, how can be used a relative new package tabularray for your table design:

\documentclass[conference]{IEEEtran}
\IEEEoverridecommandlockouts
\usepackage{textcomp}
\usepackage{xcolor}
\usepackage{tabularray}             % <--- new, used version 2021Q
\UseTblrLibrary{booktabs, siunitx}  % <--- new
\usepackage{lipsum}
\begin{document}
\lipsum[1]
\begin{table}[h!]
    \centering
    \caption{caption}
    \label{tab:my_label}
\begin{tblr}{colsep=4pt,
             colspec={@{} X[l] X[l] *{4}{S[table-format=1.3]} @{}},
             }
     \toprule
Feature 1   & Feature 2 & {{{Accuracy}}} & {{{Precision}}} &{{{ Recall}}} & {{{Specificity}}} \
    \midrule
original dna size   & compressed dna size   & 0.999 & 0.999 & 0.999 & 0.999 \
original dna size   & compression ratio     & 0.999 & 0.999 & 0.999 & 0.999 \ 
     \bottomrule
\end{tblr}
\end{table}
\lipsum[2-7]
\end{document}

Answer 2

The following makes the following changes to your table:

• Use \linewidth instead of 0.3\textwidth as the width the table might take

• Actually make use of the X-type columns by defining a new column type (called L) that'll be a left-aligned X-type column (this way TeX won't try to set the contents of these columns flush, which would only throw overfull box warnings as that's nearly impossible with narrow columns)

• Use the S-type column provided by siunitx for the numeric data (the table-format=1.3 means numbers have 1 digit before the decimal separator and 3 digits afterwards).

• Drop the standard rules provided by the LaTeX kernel, instead use the rules \toprule, \midrule, \bottomrule provided by booktabs

• To ease reading of the table put \addlinespace (also provided by booktabs) between rows which need more than a single line of text.

• Reduce the space between columns to 3/4ths using \setlength\tabcolsep{.75\tabcolsep}.

• Put the \caption above the tabular (that's what IEEEtran wants, compare the spacing of the caption to yours) and put the \label inside the mandatory argument of \caption (that is more robust in general).

• Don't use h! only as the placement, instead I used htp! (LaTeX will turn h! to ht! anyway, and allowing no p leads to problems most of the times if your table gets too big). If you want "absolutely here and no where else" you should use H provided by the float package instead.

Everything combined:

\documentclass[conference]{IEEEtran}
\IEEEoverridecommandlockouts
\usepackage{tabularx}
\usepackage{siunitx}
\usepackage{booktabs}
\newcolumntype{L}{>{\raggedright\arraybackslash}X}
\usepackage{duckuments}% dummy content for the text, don't use it in your document
\begin{document}
\blindduck
\begin{table}[htp!]% never use just h!
  \centering
  \caption{caption\label{tab:my_label}}
  \setlength\tabcolsep{.75\tabcolsep}%
  \begin{tabularx}{\linewidth}{L L *{4}{S[table-format=1.3]}} 
    \toprule
    Feature 1 & Feature 2 & {Accuracy} & {Precision} & {Recall} & {Specificity} \
    \midrule
    original dna size & compressed dna size & 0.999 & 0.999 & 0.999 & 0.999 \
    \addlinespace
    original dna size & compression ratio & 0.999 & 0.999 & 0.999 & 0.999 \
    \bottomrule
  \end{tabularx}
\end{table}
\blindduck
\end{document}