How to make ellipses in latex with the same size

Question

I hope someone can help me. How can I make both ellipses have the same size?

I attach the code and an image of how I want it to look

\begin{tikzpicture}
  \node (1) at (0,0) {1};\filldraw(1.east) circle (1pt);
  \node (2) [below of = 1] {2};\filldraw(2.east) circle (1pt);
  \node (3) [below of = 2 ] {3};\filldraw(3.east) circle (1pt);
  \node (4) [below  of=  3] {4};\filldraw(4.east) circle (1pt);
  \node[fit = (1) (2) (3) (4) , ellipse, draw=blue, minimum width =2cm,thick, label=below:\(A\)]{};
 
 \node (1_1) at (3,0) {1};\filldraw(1_1.west) circle (1pt);
 \node (2_2) [below of=1_1] {2};\filldraw(2_2.west) circle (1pt);
 \node (3_3) [below of=2_2] {3};\filldraw(3_3.west) circle (1pt);
 \node[fit = (1_1) (2_2) (3_3) , ellipse, draw=blue, minimum width =2cm,thick,label=below:\(B\)]{};
 
 \draw[->, shorten >=.1cm, stealth] (1.east) to (1_1.west);
 \draw[->, shorten >=.1cm, stealth] (2.east) to (3_3.west);
 \draw[->, shorten >=.1cm, stealth] (3.east) to (2_2.west);
 \draw[->, shorten >=.1cm, stealth] (4.east) to (1_1.west);

\end{tikzpicture}

Answer 1

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{fit,shapes,positioning}

\begin{document}
    \begin{tikzpicture}[node distance = 8mm,ell/.style={ellipse, draw=blue,thick,minimum height=6cm, minimum width=25mm, inner sep=0pt}]
      \node (1) at (0,0) {1};\filldraw(1.east) circle (1pt);
      \node (2) [below = of 1] {2};\filldraw(2.east) circle (1pt);
      \node (3) [below = of 2 ] {3};\filldraw(3.east) circle (1pt);
      \node (4) [below = of 3] {4};\filldraw(4.east) circle (1pt);
      \node[ell,fit = (1) (2) (3) (4) ,label=below:\(A\)]{};
     
     \node (1_1) at (4,0) {1};\filldraw(1_1.west) circle (1pt);
     \node (2_2) [below = of 1_1] {2};\filldraw(2_2.west) circle (1pt);
     \node (3_3) [below = of 2_2] {3};\filldraw(3_3.west) circle (1pt);
     \node (4_4) [below = of 3_3] {\vphantom{4}};
     \node[ell,fit = (1_1) (2_2) (3_3) (4_4),label=below:\(B\)]{};
     
     \draw[->, shorten >=.1cm] (1.east) to (1_1.west);
     \draw[->, shorten >=.1cm] (2.east) to (3_3.west);
     \draw[->, shorten >=.1cm] (3.east) to (2_2.west);
     \draw[->, shorten >=.1cm] (4.east) to (1_1.west);
    
    \end{tikzpicture}
\end{document}

Answer 2

A fit node is usually placed around the nodes it covers, but the reference nodes only define their size because the position can be whatever. This is what is shown in following code. Both ellipses are defined with the same fit collection of nodes which means that both will have equal dimensions, but the second is placed around right nodes. This way there's no need to fix a minimum height as is proposed in other solutions.

\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{fit, shapes.geometric, positioning, arrows.meta}

\begin{document}

\begin{tikzpicture}[> = Stealth]
  \node (1) at (0,0) {1};\filldraw(1.east) circle (1pt);
  \node (2) [below of = 1] {2};\filldraw(2.east) circle (1pt);
  \node (3) [below of = 2 ] {3};\filldraw(3.east) circle (1pt);
  \node (4) [below  of=  3] {4};\filldraw(4.east) circle (1pt);
  \node[fit = (1) (4) , ellipse, draw=blue, thick, minimum width=2cm, label=below:\(A\)] (A){};
 
 \node (1_1) at (3,-0.5) {1};\filldraw(1_1.west) circle (1pt);
 \node (2_2) [below of=1_1] {2};\filldraw(2_2.west) circle (1pt);
 \node (3_3) [below of=2_2] {3};\filldraw(3_3.west) circle (1pt);
 \node[fit = (1) (4), ellipse, draw=blue, thick, minimum width=2cm, label=below:\(B\), anchor=south] at (A.south-|1_1){};
 
 \draw[->, shorten >=.1cm] (1.east) to (1_1.west);
 \draw[->, shorten >=.1cm] (2.east) to (3_3.west);
 \draw[->, shorten >=.1cm] (3.east) to (2_2.west);
 \draw[->, shorten >=.1cm] (4.east) to (1_1.west);

\end{tikzpicture}
\end{document}

Answer 3

• Sizes of the both ellipse are already the same. Eventually it can be slightly reduced (as is done in MWE below).
• It is sensible to define common styles of for all image elements
• Using the chains library make image code a bit shorter

\documentclass[tikz,border=3.141592]{standalone}
\usetikzlibrary{arrows.meta,
                calc, chains, 
                fit,
                positioning,
                shapes}

\begin{document}
    \begin{tikzpicture}[
node distance = 8mm and 32mm,
  start chain = A going below,
  start chain = B going below,
   arr/.style = {draw, -Stealth}, 
   dot/.style = {circle, fill, inner sep=2pt, outer sep=1pt,
                 node contents={},
                 label=#1},
   ell/.style = {ellipse, draw=blue, thick,
                 minimum height=55mm, minimum width=20mm, inner sep=0pt,
                 node contents={},
                 fit=#1}
                        ]
\foreach \i in {1,2,3,4}                    
   \node (a\i) [dot=left:\i, on chain=A];
\node[ell = (a1)(a4),label=below:$A$];
%
   \node (b1) [dot=right:1, 
               right=of $(a1)!0.5!(a2)$,
               on chain=B
               ];
\foreach \i in {2,3}
   \node (b\i) [dot=right:\i, on chain=B];
\node[ell = (b1)(b3),label=below:$B$];
%%
\draw[arr]  (a1) edge (b2)
            (a2) edge (b3)
            (a3) edge (b2)
            (a4) edge (b1);
    \end{tikzpicture}
\end{document}