How humans hold and touch the device?

Guidelines

Apple - Human Interface Guidelines

In the Human Interface Guidelines, Apple recommends a minimum target size of 44 pixels (px) wide 44 pixels tall.

Android - Material Design Guidelines

In the Android Material Design Guidelines it’s suggested that touch targets should be at least 48 x 48 dp*. A touch target of this size results in a physical size of about 9mm, regardless of screen size. The recommended target size for touchscreen elements is 7–10mm.

Touch accuracy for specific parts of screen

Research

An MIT Touch Lab study of Human Fingertips to Investigate the Mechanics of Tactile Sense found that the average human finger pad is 10–14mm and the average fingertip is 8–10mm.
Most users will use a device that has a capacitive touch screen, meaning they will be familiar with using their finger pad to interact. So it’s best to aim for around 54dp/px (for all touch devices) as a minimum to limit the amount of user errors.

Combining guidelines & research

Based on the Apple & Android guidelines and MIT Touch Lab research, the recommended target size should be 7-10mm, which converting to pixels becomes 44px - 56px.

To get to an exact number, let's calculate the mean of these three recommended px sizes.

Target size to test with = 49px (Round off)

Testing

After conducting this test on three of the main screens Home, Service listing & Slot booking, here are the mapped target points on each of the UI elements on the screen

Outcomes

Issue found on below two sections.

Solution