FAQ: How to check my TV's VESA size? Which model is best for my TV?
A: First locate the 4 threaded holes at the back of your TV, then measure the horizontal/vertical distances between these holes. If horizontal = 400mm and vertical = 200mm, then your TV's VESA size is 400x200.
It is always better to choose the smallest bracket compatible with your TV because there is a lesser chance of it blocking the TV's AV ports. So if your 65" TV has VESA 400x400, the "Medium up to VESA 400x400" is a better choice than the "Large up to VESA 600x400", although both sizes are compatible with your TV.