A gaming mouse that is too big makes your hand stretch. One that is too small makes your fingers cramp. Either way you lose a little accuracy and comfort, and no sensor spec fixes that. The good news is that fit comes down to two things you can check in a minute: how big your hand is and how you hold the mouse.
Lay your hand flat on a table and measure from the crease of your wrist to the tip of your middle finger. That is your hand length. Many mouse guides group hands roughly like this: under about 17 cm is small, 17 to 19.5 cm is medium, and above that is large. These are guides, not laws, but they give you a starting point.
Width matters too. Measure across the widest part of your palm, leaving out the thumb. A wider hand often feels better on a wider shell, a narrow hand on a slimmer one.
Grip means how your hand sits on the mouse. There are three common styles, and most people use one without thinking about it.
Your whole palm rests on the mouse and your fingers lie fairly flat on the buttons. It suits a longer, fuller shape that gives the palm something to rest on.
The back of your palm touches the mouse, but your fingers arch up like a claw. A medium shape with a hump toward the back or middle works well.
Only your fingertips touch the mouse and your palm hovers above it. A shorter, lighter, lower mouse lets your fingers move freely.
Your hand length gives the base size. Your grip nudges it. A palm grip likes a little more mouse underneath it, so you can go a touch longer. A fingertip grip needs less, because your palm never touches the shell. A claw grip sits in the middle.
This is why two people with the same hand can prefer different mice. If you are between sizes, let your grip break the tie: palm, size up; fingertip, size down.
Weight is a matter of taste, but lighter mice are easier to flick and tire your wrist less over a long session. Many modern gaming mice are under about 70 g; heavier ones can feel steadier. Shape matters as much as length. A symmetrical mouse looks the same on both sides, and an ergonomic mouse is built for one hand, usually the right. Left-handed players have fewer ergonomic choices, so check this first.
Also think about your thumb. Side buttons are handy, but if your thumb rests on them by accident, a mouse with fewer buttons or a flatter side may suit you better.
A few things matter at every budget, and they matter more than brand names:
At a lower budget, aim for a comfortable, proven shape. At a higher budget you are mostly paying for lower weight, wireless and better materials. Return policies help too: a mouse you can swap if it does not fit is worth a lot.