The One Thumb, One Eyeball Test

Imaging that your user is on their phone, standing in the bus, surrounded by distractions and your app has to hold their attention. They must be able to use your product using an average thumb. If they can’t, you fail the One Thumb, One Eyeball test, and will lose users.

A woman using the mobile phone with one hand on a beach

Many mobile products have call to action buttons that are either too small, or placed too close together, or links are confusing, or new unwanted windows pop up. As soon as you redirect someone to a screen they didn’t want or expect, they’ll lift their head up and your product has lost. Users should be able to complete critical tasks quickly without losing focus. This means all the critical tasks are "do-able"using one thumb and one eyeball what come may - be it standing in the bus, leaning on to the wall at train station, sitting in a congested place at work, comfortably lying down on the couch or even better, sitting on the beach.

One Thumb, One Eyeball Test

People use mobile phones everywhere and anywhere. They are often distracted away from their mobile phones to get some work done or distracted by mobile phones to do some physical work without dropping the phone down. This forces them to use the mobile phone by investing only one eye and one thumb. This enables high speed interaction using one hand needing short attention spans.

The one thumb, one eyeball test was proposed by Luke W during the design of “Polar”, an app designed to create photo polls and allow voting on them. 

The objective was that a user should be able to create a new poll in less than a minute using only one thumb to do so. This test is now a global standard for mobile apps across the world.

Moving away from Hamburger to Tab bar design

Hamburger menu placed in top left corners of the app are too hard to access. Take a look:

A user who is driving a car needs to use the phone in one hand with the other hand on the steering wheel. If the app hamburger is in the top-left corner, the one thumb use case fails. In other words, users must be able to perform critical tasks on the mobile app with just one thumb in a few seconds. Lesser the time (in seconds), the better. Users work in micro-moments - small units of time with distracted attention. Hence the need for speed.

In the above app, notice that most of the critical tasks like My Flights, Today's Deals, Booking are easily accessible using one thumb. This is the freedom users need.

Takeaway

Effective mobile designs must accommodate for one eye and one thumb experiences.

If people can get things done in time sensitive, limited mobility situations, they'll be even more efficient and products will have their full attention.