Guide
Testing a touch screen: dead zones, ghost touches, multi-touch and pressure
A touch screen can fail in ways that are hard to notice in daily use: a strip where touches are ignored, a line that breaks up as you drag, taps that register somewhere else, or random touches when nobody is touching it. A good test is to draw all over the screen with several fingers and look at the result. This page does that, and shows what the screen reports about each touch.
How to test
Put your finger on the grey area and drag. The path appears in a colour, and each additional finger gets its own colour. Draw across the whole area, including corners and edges, then draw closely spaced lines to find gaps. Clear the drawing removes the lines and the counters. A message tells you to touch the area until something has been drawn.
A worked example
Press Sample to see the page filled with five wavy lines in five colours. The figures read Most at once 5, input type touch, and the median time from event to next frame 11.5 ms, the middle value of the six sample delays 11, 12, 9, 14, 10 and 13 ms. On a real device the line under the drawing shows, for each finger down, its pointer number, type, x and y position, pressure and contact size in pixels.
Dead zones and broken lines
A dead zone is a place where your finger draws nothing. Draw lines side by side over the whole screen, and a gap in the lines shows it. A line that breaks into dashes when you drag points to a screen that loses the touch, or to a very sluggish digitiser. Check the edges, which are the weakest part of many screens, and areas under a screen protector or case.
Ghost touches
Leave the screen untouched for a while, then watch for marks. If dots or lines appear without a finger on it, the screen is registering touches that are not there, a sign of moisture, a crack, a faulty protector or a poor charger. Try again unplugged and with the protector removed to locate the cause.
Multi-touch and the hardware limit
The page shows how many fingers are down now and the maximum reached. It also shows the hardware limit reported by the device, usually 5 or 10. Use all your fingers to reach it. Some systems take over multi-finger gestures, so you may not reach the limit in the browser. Pen and mouse input are listed under the input types seen.
Pressure, size and delay
Pressure and contact size appear only when the screen or pen reports them; many phones report a fixed value or none. The delay figure is the time from the browser receiving a touch to the next screen update. It is a rough guide to how responsive drawing feels, not a measurement of the screen’s own latency, which needs a camera or special equipment.
Edge cases
Palm rejection may ignore large touches, so a flat hand may register nothing. A web page cannot see touches outside itself, such as the edge swipes used by the system. On a laptop with a touch screen, the touchpad is not part of this test.
Limits
The test relies on what the browser reports. It cannot repair a screen or tell you the cause of a fault. Drawings are not saved.
Related tools
- Dead Pixel Test checks the display itself with full-screen colours.
- Refresh Rate Test reports how smoothly the browser draws frames on the same screen.
- Gamepad Tester tests another input device.
- Mouse Test checks pointer input from a mouse.
Checked against the current version of the Touch Screen Tester on .