Split the screen into cells to find areas that do not respond and spots where touch breaks
The touch screen test divides the screen into a checkerboard of cells and paints the cell of every touch point your browser reports as a finger passes. A cell that stays empty after you rub the whole screen evenly is a spot where no touch was reported, and a line that stops in the middle leaves an accent-coloured mark. Put down more fingers and the test counts how many are recognised at once; keep your hands off the screen and it counts ghost touches that arrive by themselves.
Dark cells have responded and light cells have not yet. As fewer cells are left, each one gets an accent outline so you can see where to rub next, and every finger touching the screen appears as a numbered circle. Full screen enlarges the board to the whole screen so you can test corners and edges. Touch data is calculated only inside this browser and is never stored or sent.
When a touch screen test helps
- Just before buying or selling a used phone or tablet: a screen that looks fine can still ignore one line or a corner. Painting the whole screen at the deal is more reliable than asking, and Copy result leaves a written record of its condition.
- After a screen replacement or repair: do not only check that the display lights up. Check that touch responds evenly all the way to the edges.
- After fitting a new screen protector or tempered glass: a thick film or a lifting edge can make one area sluggish. You can compare before and after the same way.
- After a drop, when only part of the screen does not respond: even without a visible crack, a broken sensor line makes the stroke break every time you cross it. What matters is whether the break marks repeat at the same spot.
- When the screen seems to press itself, or only misbehaves while charging: watching with your hands off shows whether untouched taps really arrive and, if so, on which side of the screen.
- When several fingers do not register in a game or drawing app: count simultaneous touches and see whether the device recognises up to the maximum it reports.
How to run the test
- Wipe the screen and dry your hands. A wet screen may not register touch properly.
- Tap Full screen. The F key works too if you have a keyboard. The board grows to the whole screen with a guide panel in the middle. Touch the board and the panel hides; lift your finger and wait a moment and it comes back.
- Rub the whole screen to paint every cell. Cover it evenly in both directions, and paint the edges by rubbing from the inside toward the edge. Cells you still have to paint are outlined in the accent colour.
- Check the break marks. Slowly pass over a mark again and see whether it breaks at the same spot. If it repeats, the mark gets a double ring and the Breaks card shows a repeat at the same spot.
- Count multi-touch by adding fingers one at a time. Each finger gets a numbered circle, and the Multi-touch card keeps the highest number counted this time.
- Run the ghost touch watch. Choose 30 s, 1 min or 3 min, tap Start watch and lift all fingers from the screen. If the trouble only appears while charging, watch once more with the charger plugged in.
- Tap Copy result. The multi-touch, painting, breaks and ghost touch results and the screen size are copied as text you can paste into a chat about a deal or a repair request.
How to read the result
One or two cells left over is not automatically a fault. Treat a spot as an area that does not respond only when it stays empty after you rub it several times from different directions. The picture below shows the same board when it is fine, when one line is empty and when only the edge cells are left.
| What you see | What it means | What to do next |
|---|---|---|
| Every cell painted and 0 breaks | The whole screen reports touch points evenly. | Go on to check multi-touch and ghost touch. |
| A few cells stay empty after rubbing several times | No touch is reported at that spot. | Wipe the screen, remove the case and screen protector and paint again. If they still stay empty, treat it as a fault in that area. |
| One vertical or horizontal line is empty and breaks repeat along it | This is the typical look of one sensor line that does not respond. | Copy the result and use it as grounds for a repair quote or a decision on the deal. |
| Only edge cells are left | The Back gesture may have grabbed the swipe first, or a case rim or a lifting protector may have blocked the finger. | Rub from the inside toward the edge, remove the case and paint again. |
| Break marks scattered, one in each place | They can also appear when the browser was briefly busy or a finger lifted slightly. | Pass over each mark again and see whether it repeats at the same spot. |
| Multi-touch lower than the device maximum | The fingers may have landed all at once, or the system may have taken them for a multi-finger gesture. | Add fingers slowly one at a time, turn multi-finger gestures off for a moment and count again. |
| Ghost touch 1 or more | Touches were reported while nothing touched the screen. | Wipe the screen, unplug accessories and the charger and watch again. If it continues, have the device serviced. |
Number of cells by screen size
The number of cells is the width and height of the board divided by the cell size (Large 56 px, Normal 40 px, Fine 28 px) and rounded to the nearest whole number. Finer cells reveal narrower faults but leave more cells to paint. A good order is to paint the whole screen at Normal first and, if you suspect a line, switch to Fine and recheck that part. The table gives full-screen sizes in CSS pixels.
| Screen | Size (CSS px) | Large | Normal | Fine |
|---|---|---|---|---|
| Phone, portrait | 390 × 844 | 7 × 15 = 105 cells | 10 × 21 = 210 cells | 14 × 30 = 420 cells |
| Small phone, portrait | 360 × 780 | 6 × 14 = 84 cells | 9 × 20 = 180 cells | 13 × 28 = 364 cells |
| Tablet, portrait | 820 × 1180 | 15 × 21 = 315 cells | 21 × 30 = 630 cells | 29 × 42 = 1,218 cells |
| Laptop | 1280 × 800 | 23 × 14 = 322 cells | 32 × 20 = 640 cells | 46 × 29 = 1,334 cells |
How breaks are detected
While a finger moves, the browser reports touch points at very short intervals. The test joins two consecutive reports with a line to paint cells, but in these three cases it leaves a break mark instead of joining them.
- Reports stopped inside one stroke: your finger stayed down, no report arrived for more than 0.08 s, and then one arrived more than 1.2 cell widths away. The stretch in between is treated as unread and is not painted.
- The position jumped inside one stroke: your finger stayed down, but one report landed more than three times the distance expected from the speed just before, and more than 0.8 cell widths away. When the finger crosses a line that does not respond, the position tends to stay on the near side and then jump across all at once.
- The finger lifted and landed again at once: while no other finger is touching, within 0.12 s after the touch of a finger that moved more than one cell width ended, a new touch starts within three cells ahead in the same direction. The sensor is taken to have lost the finger briefly.
Reports can also arrive late when the browser is briefly busy, so a single mark alone does not prove a fault. A mark whose centre appears within 1.5 cells of an earlier mark is counted separately as a repeat at the same spot. A screen with a broken sensor line breaks at the same place every time you cross it, so a rising repeat count is the clearest clue.
Multi-touch count and the value the device reports
The value the device reports on the Multi-touch card is the browser's navigator.maxTouchPoints, the largest number of simultaneous touch points the device supports. MDN says phones typically return 5, and WebKit, the engine behind Safari on iPhone and iPad, returns 5 whatever the device. So the test counts the result as normal when the highest number you counted reaches the reported value (capped at 10).
If all the circles vanish when you put many fingers down, it is usually not a fault. A browser can cancel every active pointer when too many touch at once, and the iPad handles four-finger and five-finger multitasking gestures, such as going to the Home Screen or switching apps, before the page. In that case add your fingers slowly one at a time, or turn the gestures off for a moment in the Multitasking & Gestures settings and count again.
Where to look first on each device
| Device | What to try first |
|---|---|
| iPhone / iPad | Restart the device, make sure the screen is clean and free of debris or water, disconnect any Lightning or USB-C accessories, and remove any cases or screen protectors. If it works without the accessories, try a different outlet, cable or charger. If it is still the same, set up service. |
| iPad, several fingers | In the Multitasking & Gestures settings, turn off the four-finger and five-finger gestures and count multi-touch again. |
| Galaxy | If you fitted a screen protector, turn on Settings > Display > Touch sensitivity. The phone diagnostics in the Samsung Members app can check the touch screen. |
| Pixel | On a Pixel 8a or earlier, turn on Screen protector mode in Settings > Display & touch > Touch sensitivity. On the Pixel 9 series, run the touch diagnostic test and see whether Adaptive touch helps. |
| Android in general | Turning on Pointer location in developer options draws the coordinates and path of each touch over the screen, and Show taps draws a circle where you touch. You can compare them with this test at the same spot. |
| Windows touch laptop | Restart the device and check for Windows updates. If it is still the same, contact the device manufacturer. |
Common mistakes
- Swiping toward the inside from the very edge: Android phones with gesture navigation use an inward swipe from the left or right edge as Back. Edge cells get painted by rubbing from the inside toward the edge.
- Stopping after painting only the board on the page: a board on the page tests only the part it covers. To reach the screen edges, paint in full screen. A result painted in full screen stays when you return to the page, and Continue test lets you paint the rest. Entering full screen lays out new cells to fit the screen, so cells painted on the page board are cleared.
- Painting with a mouse or touchpad: cells painted with a mouse stay faint and do not count in the touch result. On a touch laptop or a tablet with a keyboard, paint with your finger.
- Calling one break mark a fault: a mark can appear once right after you open the page or while another app is busy. Look for repeats at the same spot.
- Blaming the screen for sluggishness under a protector: a thick film lowers sensitivity. Turn on Touch sensitivity or Screen protector mode and compare again.
- Watching for ghost touch only without the charger: a problem that appears only while charging shows up only if you watch with the charger plugged in.
- Rotating the screen during the test: a new orientation changes the cell layout a lot, so the cells are laid out again. Finish painting in one orientation before you rotate.
Limits of this test
- It sees only the centre of the touch point the browser reports. It does not measure pressure, contact area or the offset between where you pressed and the reported coordinates.
- Gestures the operating system takes first (Back, multitasking) and the system bar areas at the top and bottom cannot be tested. Safari on iPhone has no element full screen and uses a view that covers the window, so a part of the top and bottom edges covered by the browser interface is missed too.
- Safari on iPhone and iPad reports 5 as the maximum number of simultaneous touches whatever the device. This value may not be the hardware spec.
- Breaks are estimated from the gaps and distances between reports. If the browser gives no dense samples (getCoalescedEvents), the judgement can be coarser for very fast strokes.
- Ghost touch counts only what arrives while you watch. For a symptom that appears only now and then, lengthen the time or watch again in the situation where it appears (for example, while charging). While you watch, supported browsers keep the screen on; if the screen still turns off or you switch to another app, that watch stops without a result.
- This test does not confirm a fault. If the same symptom repeats, confirm it with the maker's diagnostics or a service centre check.
Reference date Setting menu names and source documents were checked on 2026-10-28. Menu names and locations may change when the operating system or apps are updated.
Sources
- 01MDN: Navigator.maxTouchPointsThe largest number of simultaneous touch points the device supports; phones (Android and iOS) typically return 5
- 02WebKit source: Navigator.cppBuilds that use iOS touch events return 5 for maxTouchPoints
- 03MDN: pointercancel eventFired when the browser will no longer deliver a pointer; may fire for every pointer when too many are active
- 04MDN: touch-actionWith none, the browser does not handle panning or zoom gestures
- 05MDN: PointerEvent.getCoalescedEvents()Dense samples of movement events merged into one; secure contexts (HTTPS) only
- 06MDN: Element.requestFullscreen()Compatibility data: not supported in Safari on iPhone, partial support on iPad from 16.4
- 07Android Developers: Gesture navigationSystem Back gesture = an inward swipe from the left or right edge of the screen
- 08Android Developers: Configure on-device developer optionsPointer location (coordinates and path) and Show taps (a circle where you touch) in the Input section
- 09Android 16 Compatibility Definition, section 7.2.4Touchscreen devices must report the multitouch, distinct and jazzhand feature flags that match the screen
- 10Apple Support: If the screen isn't working on your iPhone or iPadRestart, clean the screen, disconnect Lightning or USB-C accessories, remove cases and screen protectors, then service if still the same
- 11iPad User Guide: Change Multitasking & Gestures settings on iPadFour-finger and five-finger gestures for the Home Screen and switching apps; turn them off or on in settings
- 12Samsung: Troubleshoot touchscreen issues on a Samsung Galaxy deviceScreen protector and Touch sensitivity (Settings > Display); the Samsung Members app's phone diagnostics
- 13Google Pixel Help: Fix touch & response issues on your Pixel screenScreen protector mode under Touch sensitivity (Pixel 8a and earlier); touch diagnostic test and Adaptive touch on the Pixel 9 series
- 14Microsoft Support: What to try if a touchscreen doesn't work in WindowsRestart the device, check for updates, contact the device manufacturer
Frequently asked questions
How do I run a touch screen test?
Tap Full screen and rub the whole screen to paint every cell. If some cells stay empty, rub them several times; if they still do not paint, that area does not respond to touch. Then add fingers one at a time to check multi-touch, and finally run the ghost touch watch with your hands off the screen.
How many simultaneous touches count as normal?
The test treats it as normal when the screen recognises the device maximum the browser reports (maxTouchPoints). Phones usually report 5, and Safari on iPhone and iPad reports 5 on every device. If you put that many fingers down and the number falls short, add them slowly one at a time and check again.
The circles all vanish when I put four or five fingers down. Is it broken?
Usually not. The iPad has multitasking gestures with four or five fingers that go to the Home Screen or switch apps, and a browser can cancel all active touches when there are too many fingers. Turn the gestures off for a moment in the multitasking gestures setting, or add your fingers slowly one at a time and check again.
How do I check for ghost touch?
In the Ghost touch card, pick a watch time, tap Start watch and lift all fingers from the screen. The test counts the touches that arrive while you are not touching and marks their positions on the board. If the problem only appears while charging, watch again with your usual charger plugged in and compare it with the result without accessories, as Apple advises.
If some cells will not paint, is the screen faulty?
First wipe the screen, remove the case and screen protector and paint again. If the same spot still stays empty or breaks again at the same place, the touch sensor in that area probably is not reporting. Seeing the picture and reading touch are separate functions, so check the display for dead pixels separately.
Only the cells at the screen edge will not paint.
On Android phones with gesture navigation, an inward swipe from the left or right edge works as Back. Paint edge cells by rubbing from the inside toward the edge, and check for a thick case rim or a screen protector lifting at the edge. On iPhone, the part at the top and bottom covered by the browser cannot be tested.
Touch got sluggish after I put on a screen protector.
On a Galaxy, turn on Settings > Display > Touch sensitivity to raise sensitivity under a protector. On a Pixel 8a or earlier, open Settings > Display & touch > Touch sensitivity and turn on Screen protector mode. After changing the setting, paint the cells again with this test to see the difference.
What else should I check when buying a used phone?
You can check dead pixels on the display, left and right speaker sound, the microphone and the cameras in the same place. On a Galaxy you can also run the phone diagnostics in the Samsung Members app for the touch screen. Pasting the text from Copy result into the chat keeps a record of the phone's condition at the time of the deal.