How to set svg width and height?

i have a 3 svg icon with different viewBox value.

<svg viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"></svg>
<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 16"></svg>
<svg viewBox="0 0 30 30" xmlns="http://www.w3.org/2000/svg"></svg>

How i can set my svg width and height with same value, so all of these 3 icon will have the same size.

<div>
    <span>
          <svg></svg>
    </span>
</div>