Touch screen test

How to test a touch screen

1. Take off a screen protector if you can, wipe the glass dry and take off gloves. Tap Start touch test.
2. On the grid, slide one finger slowly over every cell until the whole screen is filled. Tap Move bar to reach the cells under the control bar.
3. Tap Show what I missed. Go back over each outlined or red cell. A cell that will not fill from any direction is a dead spot.
4. Switch to Draw and draw slow straight lines edge to edge, across and down. A working screen draws a solid line; a dead strip breaks every line at the same place.
5. Switch to Fingers and add fingers one at a time to see how many it tracks, then to Edges to check the outermost 5 mm all round.
6. Tap Reset to start over, or Leave (Esc on a keyboard) to see the results.

How the dead-spot grid decides

A touch screen does not report a continuous line. It reports where your finger is many times a second, and the browser hands the page each report. Moving at 10 cm a second, a screen that reports 60 times a second gives a point every 1.7 mm. The grid fills every cell on the straight line between two consecutive reports, because your finger passed over them.

When two reports in the same stroke are more than 48 CSS px apart, the page treats that as a gap: the screen lost your finger on the way. The cells at both ends fill, and the empty cells in between are flagged red as likely dead spots. A fast flick also makes gaps, which is why the steps say slowly. A flagged cell turns to filled the moment the screen reports a touch inside it, so a one-off gap clears itself when you go over it again. A real dead spot stays red, or refuses to fill, every time.

Worked example: on a phone 390 px wide the medium grid has 10 columns of 39 px. You slide along the third row at a steady pace and the screen reports points 8–15 px apart, then nothing for 130 px, then reports again. The page counts 1 gap, and the empty cells the jump crossed (2 or 3 at this size) turn red. Slide back over them slowly: if they fill, it was a hiccup; if the line breaks at the same place again, that strip of the digitiser is not sensing.

Cell sizes, edges and fingers

Fine cells aim at 24 px, medium at 40 px and coarse at 64 px, stretched slightly so whole cells fill the screen. Fine cells are narrower than a fingertip, so they show exactly where a dead line runs; coarse cells are quick to fill for a first pass. Changing the size starts the grid again.

The edge strips are 5 CSS mm wide (19 CSS px; a CSS millimetre is defined as 96/25.4 px, so on most phones it is smaller than a real one) and cut into pieces about 40 px long. The edge is where a cracked corner or a lifted protector usually shows first, and where phones put their own gestures.

In Fingers, each finger gets a numbered circle. If the browser passes on the contact size or the pressure, it is shown with the label reported by your device. A device that reports neither shows nothing rather than a guess.

What it cannot do

• It cannot fix a screen. It shows where touch fails so you can decide on a repair, a return or a warranty claim.
• It cannot tell a screen-protector problem from a digitiser fault: an air bubble, a crack in the protector or a thick glass protector blocks touch just like a fault. Test again with the protector off before you blame the screen.
• Pressure (force) and contact size are shown only where the device reports them. It cannot measure them itself.
• Gestures at the very edge (the back swipe, the notification or Control Centre pull, the home bar) may be taken by the phone before the page sees them, so an edge piece that will not fill by swiping in can still be fine: tap it, or start inside and slide outwards.
• It sees only what the browser passes on. Ghost touches (the screen tapping by itself) show as filled cells you did not touch, but the page cannot tell them from yours; watch the screen with your hands off.
• On iPhone it cannot test under Safari's bars or the status bar, because iPhone Safari gives pages no full-screen mode.

Privacy

Nothing leaves your device and nothing is saved. The page sends an anonymous page-view count and one of two fixed words, touch-start and touch-multi; never where you touched or how many fingers.

Questions

How do I test a touch screen online?

Open this page on the phone or tablet itself and tap Start touch test. The grid covers the screen; slide one finger slowly over every cell until all of them are filled, then tap Show what I missed. Any cell that will not fill however you approach it, and any cell flagged as a likely dead spot again and again, is where the screen is not sensing touch. Nothing to install.

How do I test the touch screen on an iPhone?

Open the page in Safari and tap Start touch test. iPhone Safari does not let web pages go full screen, so the test fills the Safari window and the address bar and the strip at the very top stay. To test those areas too, add the page to your Home Screen with Share, Add to Home Screen, and start it from that icon. Swipes that start at the bottom edge or the top-right corner can be taken by iOS (home and Control Centre) before the page sees them.

How do I test the touch screen on an Android phone?

Open the page in Chrome, Samsung Internet or Firefox and tap Start touch test: the page goes full screen and hides the status and navigation bars. Fill the grid, then switch to Edges to check the outermost 5 mm. A swipe that starts at the very left or right edge may be taken by Android's back gesture and a swipe from the top edge by the notification shade; start those strokes a little inside the screen and slide outwards. Many Android phones also have a built-in test in a service menu, but the codes differ by maker.

Does it work on an iPad or Android tablet?

Yes. On a tablet the grid simply has more cells. iPad Safari can show the test full screen (from iPadOS 16.4), and a swipe down exits it; tap Start again to go back in. Rotate the tablet to test the other orientation: the grid is rebuilt for the new shape and starts empty.

How many fingers can my screen detect at once?

Switch to Fingers and put fingers down one by one. Each finger gets a numbered circle and the page keeps the highest count as Most at once. The page also shows the number of touch points your browser says the screen supports. If the count drops when you add a finger, or a circle jumps between two fingers, the screen has reached its limit or is merging touches that are close together; spread your fingers out and try again.