The importance of minimising interaction cost in UX design

What is interaction cost?

“The interaction cost is the sum of efforts — mental and physical — that the users must deploy in interacting with a site in order to reach their goals”

RALUCA BUDIU, Nielsen Norman Group

I regularly refer back to an article by Nielsen Norman Group (N/N Group) on interaction cost. According to N/N Group the ideal interaction cost is zero.

With an interaction cost of zero, when a user visits a website the information they need will be right in front of them, no effort required.

However, as we all know zero interaction cost is rarely attainable. Most task require some level of cognitive effort, whether clicking a link, scrolling down a page or scanning a page of text.

When thinking about interaction cost a UX should be looking to minimise the cognitive effort, interaction cost – required to achieve user goals.  Ultimately this should result in higher conversion rates and reduce drop off.

Key Factors in reducing interaction cost

According to the N/N Group some of the key factors that can effect interaction cost, and therefore UX designers should try to be reduce include:

  • Reading
  • Scrolling
  • Looking around in order to find relevant information
  • Comprehending information presented to you
  • Clicking or touching (without making mistakes)
  • Typing
  • Page loads and waiting times
  • Attention switches
  • Memory load ­– the information that users must remember in order to complete their task

Interaction cost applied

Levi's interaction cost

Levi’s is a great example of where interaction cost has been considered when buying clothes online.  Instead of hiding options in drop downs the designers have placed the options directly on the page.

In contrast the all to familiar journey of choosing clothes online often follows this pattern, resulting in a high interaction cost.

1. Select a drop down to choose the item colour 

2. Read the list of colours in the drop down

3. Select the colour you would like

4. Select a drop down to choose the item size

5. Read the list of sizes and see your size has sold out. Exit the site

Levi’s have lowered the interaction cost of the clothes selection process by making information that once required three clicks to view immediately visible to the user.


With one click I can see if the colour of jeans I want are available in my size and length.  No drop downs needed.


Interaction cost is generally a good measure of how difficult an interface will be to use for a user.

While the way a product is marketed and branded usually increases the user motivation and expected benefits for engaging with a site; a large part of usability deals with lowering the interaction cost

When accessing designs against each other, comparing the interaction cost can help you understand which design is more likely to be successful.

The original N/Ngroup article going into more detail on the subject can be found here.