You set both mice to 1600 DPI. They don't move the same. Here's what's actually happening.
If you've ever switched mice, matched the DPI number exactly, and still felt like your aim was slightly "off" for no reason — you weren't imagining it. In most cases, the two mice were never moving at the same real speed in the first place, even though the number on screen said otherwise.
The "1600 DPI" printed on a mouse's packaging isn't a measured fact — it's the value the manufacturer's firmware is aiming for. Optical sensors don't naturally land on round numbers. When you actually measure how far the cursor moves for a fixed physical distance, a mouse labeled 1600 DPI might really be tracking at 1583, or 1627, or somewhere else nearby. The gap is usually small in percentage terms, but it's large enough to notice in a fast flick or a tight tracking duel.
The part that trips people up: two mice can share the exact same sensor chip and still track differently at "the same" DPI. That's because the DPI you see in software isn't the raw sensor output — it passes through firmware calibration that each brand writes independently. How close that firmware lands to the target number, and where it rounds internally, is a decision each manufacturer makes on its own. Add in unit-to-unit manufacturing tolerance and how the lens interacts with a given mousepad surface, and "1600" stops being a single, comparable value across brands.
The most common way people try to match sensitivity across mice is a straight ratio: new DPI = old DPI × old sensitivity ÷ new DPI. That formula only works if both mice track at exactly their labeled DPI — which, per the above, is rarely true. Do the math correctly and you can still end up with a setup that feels wrong, because the math was built on a number neither mouse actually produces. This is the specific gap RealDPI's calculator is built to close: instead of matching labels, it matches each mouse's own measured tracking speed at that setting.
If a new mouse feels off at a DPI that "should" match your old one, work through this order instead of guessing: