Spiral Window Balance

This appears to be a typical tilt window, so you only have two options available: either the 3/8" diameter Series 900 or the 9/16" diameter Series 600. You need to measure the diameter of the tube for the original to verify the better match.

In regards to length, the height of the window is not what you want to measure. Instead, you measure the tube. Just make sure the balance is removed and undamaged before you measure. Your spring is sticking out of the tube at the bottom there, which is uncommon. The tube should go all the way to the plastic bearing. If yours is for whatever reason shorter than average, you need to compensate.