If you mean to put one next to the other, leaving resolution aside...
Your 24" monitor screen should be 53,13 x 29,89
while the 34" ultrawide around 79,57 x 33,57
So +3,68 cm difference
A 29" ultrawide, with 67,87 x 28,63 would make only -1,25cm difference which, if you plan to run em alongside, may fit better the purpose.
PD: Theoretical size and refering ONLY to screen size, it may vary ±mms among brands and models.
PD2: Didn't notice date, hope it still helps you.