Contact Area Logger

How the Contact Area Logger Works

The Contact Area Logger records the width and height of each contact, as reported by the device, and calculates the contact area in square millimeters. Devices that report no size give a width and height of 1 px, which the tool flags.

1. Touch with a fingertip: The tool reads width and height from the pointer event.
2. Try a flat finger: Press the pad of the finger to see a larger contact.
3. Read the log: Each row shows width, height and area in px² and mm².
4. Compare contacts: See fingertip, thumb and palm contact sizes side by side.

Contact Area Logger Formula

The Contact Area Logger area equals the area of an ellipse with the reported width and height.

Width, Height

Contact size in CSS pixels

π

3.1416

0.07

Square millimeters per square CSS pixel

Example: A contact measures 40 × 30 px. Area = 3.1416 × 20 × 15 = 942.5 px², which equals 66.0 mm² (0.10 in²).

Contact Area Logger Reference Table

The Contact Area Logger conversion table lists typical contact sizes and areas.

About the Contact Area Logger

A Contact Area Logger is a data tool that measures the size of each touch on the screen. Contact size tells a fingertip apart from a thumb or a resting palm.

The Pointer Events API reports contact width and height in CSS pixels. Operating systems use contact size for palm rejection: a contact much larger than a fingertip is treated as an accidental palm touch.

Ways to Use the Contact Area Logger

There are 5 main uses of the Contact Area Logger, including palm-rejection testing and target sizing research.

• ✓Palm-rejection testing: Developers find the size above which contacts get rejected.
• ✓Target sizing research: Designers compare fingertip size with button size.
• ✓Hardware support checks: Users find whether a device reports contact size at all.
• ✓Child-focused design: Teams measure smaller contacts from young users.
• ✓Glove testing: Testers compare contact size with and without gloves.