Touchscreen Test
Paint the screen with your finger to find dead zones, trace the edges, and count how many touches it tracks at once. Shows pressure and contact size where the screen reports them, and works full screen.
How to Use
- Press Start test or touch the pad. While the test runs, touches on the pad draw instead of scrolling; touch outside the pad to scroll the page.
- Swipe slowly over the whole pad, row by row. Every cell your finger crosses fills in; the coverage climbs towards 100 %. Press Full screen to test the whole display.
- Look for cells that stay empty although you swiped over them, and for red dots: a red dot is where a stroke dropped out and landed again moments later, the sign of a dead strip.
- Choose Edges and trace all four sides right up to the bezel, then Multi-touch and put fingers down one at a time to see how many the screen tracks.
- With a stylus, try Pressure: circles grow with pressure if it is reported. Stop test gives the pad back to the page. On a computer without a touch screen the mouse paints as a demo.
Nothing is recorded or sent: touches stay in this tab. The pad only stops the page scrolling while a test runs.
Touches now
| # | Type | x, y px | Pressure | Size px |
|---|
| ms | Event | Note |
|---|
Worked Example
The example on a plain visit. A 960 × 360 px pad is split into 32 × 12 = 384 cells of 30 × 30 px. Twelve swipes, one along each row, run from 4 % to 96 % of the width, and five of them (rows 5 to 9) cross a dead strip. The swipes fill 350 cells: 350 ÷ 384 × 100 = 91.1 % coverage.
The breaks. On row 5 the touch “lifted” at 595 px (2,904.0 ms after the first touch) and a new touch landed at 672 px at 2,949.0 ms. That is 45 ms later and 76.8 px away, 7.5 % of the 1,025 px diagonal: under both limits (150 ms and 15 %), so it is a break, drawn as a red dot. The same happened on rows 6, 7, 8 and 9, and the two columns in between, 21 and 22, never filled: a 10-cell dead patch.
Edges. The outer ring has 32 + 32 + 10 + 10 = 84 cells. The swipes filled 30 of the 32 top cells and 30 of the 32 bottom cells but never reached the outer 30 px column on either side: 60 ÷ 84 = 71.4 %, with the left and right edges at 0 %.
The common mistake: reading 91.1 % coverage as “8.9 % of the screen is dead”. Of the 34 empty cells, 24 are edge cells the finger simply never reached; only the 10-cell patch is suspect, and 10 ÷ 384 = 2.6 % of the screen. Trace the edges before calling them dead.
Report rate. One finger moving for 500 ms gave 61 samples, so 60 intervals: 60 ÷ 0.5 s = 120 Hz, the touch sampling rate, which can differ from the display’s refresh rate.
Show Work
How Each Measurement Works
getCoalescedEvents() of one moving finger.How a Touchscreen Finds Your Finger
Projected capacitive screens, used in almost every phone and tablet, have a fine grid of transparent electrodes under the glass. A finger changes the capacitance where it sits, and the touch controller scans the grid many times a second to work out where. That is why one broken electrode line, from a crack or a flexed cable, kills a whole strip, and why water, a poor screen protector or a noisy charger can create touches that are not there. Edges are hardest to read because there are fewer electrodes on one side of the finger, so they are worth testing on their own.
Two rates. The touch controller has its own sampling rate, often 120 Hz or 240 Hz on phones, separate from the display’s refresh rate. A browser hands the page one move per frame and keeps the samples in between in getCoalescedEvents(), which is how this test counts them.
In the browser. The W3C Pointer Events standard gives touch, pen and mouse one set of events, with pointerId for each finger, pressure, and width/height for contact size; navigator.maxTouchPoints reports how many touches the device supports. The CSS touch-action property, which this pad switches to none only while testing, tells the browser not to scroll or zoom on touches there.
History. E. A. Johnson of the Royal Radar Establishment in Malvern, England, described a capacitive touchscreen in 1965, for air-traffic control. Resistive screens, two conductive layers pressed together, dominated PDAs and early phones; Apple’s iPhone of 2007 brought multi-touch capacitive screens to the mass market.
About This Tool
Reference: Dead Pixel Warranty Policies by Brand.
This touchscreen test turns the pad into a grid that fills where you touch, reports total and edge coverage, finds the largest untouched patch inside the edges, flags breaks and jumps, counts simultaneous touches against what the device claims, reads pressure and contact size, and estimates the touch report rate. Full screen tests the whole display where the browser allows it.
Privacy: nothing is recorded, stored or uploaded; touches stay in this tab. The pad stops the page scrolling only while a test runs, and touching outside it always scrolls. On a computer without a touch screen the tool says so and lets the mouse paint as a demonstration.
Sources: W3C Pointer Events (pressure, width/height defaults, coalesced events, maxTouchPoints, touch-action), the WHATWG Fullscreen API, and MDN Web Docs for browser support.
Related tools: Dead & Stuck Pixel Test, Mouse Tester, and Keyboard Tester.
Frequently Asked Questions
How do I find dead zones on my touchscreen?
Paint the whole pad slowly until it is covered. A dead zone shows up two ways: cells that stay empty however often you swipe across them, and red dots where a continuous swipe broke. In the example, five swipes all dropped at the same place: each finger “lifted” and landed again 45 ms later, 77 px further on, leaving a 2 × 5-cell empty patch. A finger cannot lift and land that fast on purpose, so a column of breaks in one spot is a fault in the touch layer, often from a crack.
How many touches can my screen detect at once?
Browsers report the screen’s own figure as navigator.maxTouchPoints, commonly 5 or 10 on phones, tablets and touch laptops; the tester shows it next to the most fingers it actually saw at the same time. Use Multi-touch mode and put fingers down one by one. If the count stops below the maximum, or a touch vanishes when you add another, the screen or its driver cannot track that many. A computer without a touch screen reports 0.
Does my touchscreen measure pressure?
Most phone and tablet screens do not. The Pointer Events standard says a device without pressure sensing must report 0.5 while touching, and a contact size of 1 × 1 px when it cannot measure the finger, so the tester shows “not reported” for those. Pens such as an active stylus usually do report pressure from 0 to 1, and many Android screens report the contact width and height of a finger.
Why will full screen not work on my iPhone?
Safari on iPhone only lets video go full screen; a web page cannot make another element fill the display there, so the tool says so instead. Turn the phone sideways for more room, or add the page to the Home Screen. Safari on iPad, and Chrome and Firefox on Android, Windows and macOS, support full screen; Esc or the Exit full screen button leaves it.
What causes ghost touches and jumps?
A ghost touch is one you did not make; a jump is a touch that leaps across the screen faster than a finger can move (the tester flags more than a quarter of the diagonal in under 40 ms). Common causes are a cracked or delaminated screen, a badly fitted screen protector, water or sweat on the glass, and electrical noise from a cheap charger. Test again unplugged and with a dry screen: if the faults go away, the screen itself is fine.
Common Use Cases
Buying a second-hand phone
Paint the whole screen in full screen and check every edge: 100 % coverage with no red dots in a few minutes is a good sign.
After a drop or a crack
Several swipes breaking at the same line, like the five in the example, show exactly where the touch layer is damaged.
Touch laptops and gestures
Three- and four-finger gestures need the screen to track that many touches; Multi-touch mode shows the count, such as 10 of 10.
Stylus and drawing tablets
Pressure mode shows the range a pen reports, for example 0.05 to 0.98, before you rely on it in a drawing app.
Ghost touches on a kiosk or car screen
Leave the test running: jumps and breaks appear in the log with timings, which helps tell a faulty screen from electrical noise.
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