16:9 monitor has a sqrt(16^2 + 9^2) = 18.358 ratio diagonal. That is, the ratio of is width, height, and diagonal are 16 by 9 by 18.358.
A 24" monitor has a 24" diagonal. So its other two dimensions are:
16 * 24 / 18.358 = 20.92" wide
9 * 24 / 18.358 = 11.77" tall
You don't give the aspect ratio for the ultrawide monitor you're considering. So you'll have to do the math I've shown above to figure out its vertical and horizontal dimensions.