Work out eDPI and how far you move the mouse for a full turn.
eDPI is DPI multiplied by in-game sensitivity, and it is the only fair way to compare your sensitivity with someone else's — a sensitivity of 2 means nothing until you know what DPI it is running on. The more practical figure is cm/360: how far you physically drag the mouse to spin all the way around.
The maths: eDPI = DPI × in-game sensitivity. cm/360 = (360 ÷ (eDPI × the game's yaw factor)) × 2.54. The yaw factor is how many degrees the view turns per mouse count, and it differs from game to game — which is why the same eDPI produces different turn distances in different games.
Measured in cm/360: under about 20 cm is high sensitivity, 20 to 40 cm is medium, and over 40 cm is low. Competitive shooter players tend to sit between 25 and 45 cm, which favours accuracy over fast turning.
For most modern sensors it makes little practical difference, since they track accurately across their whole range. Common practice is 800 or 1600 DPI with in-game sensitivity adjusted to taste. Avoid very low DPI with very high in-game sensitivity, which can make small movements coarse.
Because each game turns a different amount per mouse count. Two games at identical eDPI can need noticeably different hand movement for the same turn — which is why cm/360 is the number worth matching when you move between games.
Yes, and it makes the figure unreliable. With acceleration on, the same physical movement produces different turns depending on how fast you moved. Turn it off in both the game and your operating system if you want a consistent cm/360.
Most sit between 400 and 1600, with 800 the most common. The DPI number itself matters far less than settling on one and leaving it alone long enough to build muscle memory.
Post it in the forums and someone who has had the same fault will usually know whether it is worth cleaning, repairing or replacing. You do not need an account to read, and it is free to join.