Make a <div> square when there is a dynamically changing width based on percentage

Question

I am working on a web app that will generate an NxN grid based on the user's selection of N. I want the total width of the grid to be relative (ie 100% of the available space) so that users can print on various paper sizes.

I can easily calculate the width of the squares in the grid by % (ie: 100%/N), but I am having issues calculating the height. The height of a web page is always going to be infinite unless I artificially limit it which, like I said, I don't want to do.

How can I make the squares in my grid be square versus rectangular when the height and width constraints of my grid are dynamic and not square?

Answer 1

There are 2 main techniques to keep the aspect ratio of a responsive element, using padding and vw units :
(for a complete solution for a responsive grid of squares, you can see this answer)

Using vw units

You can use vw units to make your elements square and responsive (viewport units on MDN).
1vw = 1% of viewport width so you can set the height of the elements according to the width of the viewport (or height with vh units).
Example with a 4x4 grid :

body{
  margin:0;
  display:flex;
  flex-wrap:wrap;
  justify-content:space-around;
}

div{
    width:23vw; height:23vw;
    margin:1vw 0;
    background:gold;  
}

<div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div>

The same behaviour can be achieved sizing the element accoring to the viewport height usin vh units.

---

Using padding

Padding is calculated according to the containers width so you can use it to set the height of block according to it's width.
Example with a 4x4 grid :

.wrap {
    width:80%;
    margin:0 auto;
}
.wrap div {
    width:23%;
    padding-bottom:23%;
    margin:1%;
    float:left;
    background:gold;
}

<div class="wrap">
    <div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div>
</div>