Mouse Scroll Wheel Test
Scroll and tilt the wheel inside the box. The test counts every step, measures the notch size, and catches steps that jump the wrong way mid-flick, which is the usual sign of a worn wheel.
Scroll about 20 steps up and 20 down with quick flicks.
More Hardware Test Tools
This test counts every step your scroll wheel sends and checks whether any step goes the wrong way in the middle of a flick. That reversal is what makes a page jump back while you scroll, and it usually means the wheel's encoder is dirty or worn. The test also measures the notch size, tilt steps and how fast you can spin the wheel.
How to Test a Scroll Wheel
- Put the pointer inside the box. The page will not scroll while it is there.
- Make about twenty quick flicks down, then twenty up.
- Scroll slowly one notch at a time for a few notches each way.
- Tilt the wheel left and right if it tilts.
- Check Backward Steps and the message under the box.
Reading the Results
| Reading | What it tells you |
|---|---|
| Backward Steps above 0 | A step went the wrong way mid-flick. Repeated counts on steady scrolls point to the encoder |
| Notch Size, e.g. 100 pixels or 3 lines | A notched wheel. Every step is the same size |
| Notch Size: No single size | A free-spinning or high-resolution wheel, or a touchpad |
| Top Speed | The most steps in one second. It depends on how hard you flick, so it is not a pass or fail number |
| Last Delta (X, Y) | The raw values the browser reported for the latest step |
Why Notch Size Changes Between Browsers
A browser reports each wheel step as a distance plus a unit: pixels, lines or pages (the WheelEvent deltaMode value). Windows sets how many lines one notch scrolls, 3 by default, and each browser turns that into its own distance. So the same mouse can show different notch sizes in Chrome and Firefox. What matters for a notched wheel is that the size stays the same from step to step.
Skipping, Jumping and Doing Nothing
- Jumps the wrong way: backward steps. Try compressed air in the wheel gap while turning the wheel.
- Some notches do nothing: scroll one notch at a time and watch the count. If the count does not move for a notch you felt, the encoder is missing steps.
- Only scrolls sideways: check that Shift is not stuck and that the mouse software has not remapped the wheel.
To check the buttons as well, run the mouse test.
Scroll Wheel Questions
What is a backward step?
One wheel step in the opposite direction in the middle of a flick, for example down, down, UP, down. The test counts it when steps on both sides go the other way and arrive less than 150 ms apart. It is the usual sign of a dirty or worn wheel encoder.
My page jumps up while I scroll down. Is the wheel broken?
That is exactly what backward steps look like. Run the test with about twenty flicks each way. If the count keeps rising on steady scrolls, the encoder is the likely cause.
What does notch size mean?
The scroll distance the browser reports for one step, with its unit (pixels, lines or pages). On a notched wheel most steps share one size. If no single size covers most steps, the wheel is free-spinning or high-resolution, or you are using a touchpad.
Why does the test say the backward check does not apply?
Smooth wheels and touchpads send many small steps of different sizes and can reverse naturally, so a reversal does not mean a fault there.
How many lines does one notch scroll?
Windows scrolls 3 lines per notch by default, adjustable in the mouse settings. Browsers then convert that to their own distance, so the notch size here can differ between browsers on the same mouse.
Why do tilt counts stay at zero?
Your wheel may not tilt, or the mouse software has remapped tilt. Holding Shift while scrolling also turns a normal wheel sideways, so the test ignores sideways steps sent with Shift held.
Can I fix a jumping scroll wheel?
Dust in the encoder is a common cause. Short bursts of compressed air into the wheel gap while turning the wheel sometimes fix it. If not, the encoder can be replaced or the mouse repaired under warranty.
Last updated October 2026. Delta units from the WheelEvent deltaMode values; Windows default from its mouse settings.