Pareto Principle

The Pareto Principle (or the 80/20 rule) states that ~80% of effects come from ~20% of the causes.

Crops on farm land with mountains in the background.


You may have inadvertently encountered The Pareto Principle before in your life, which states that 80% of consequences come from 20% of the causes.

The principle is named after Vilfredo Pareto, an Italian economist, who noticed that approximately 80% of the land in Italy was owned by 20% of the population (hence the image of farm land at the top of the page...)

This principle is useful when helping to prioritise time. It could be found that 80% of the problems your users are facing could be solved by fixing 20% of the usability issues on your product, which helps your prioritise these. It could also be found that 80% of your companies revenue comes from 20% of your customers, helping you prioritise these people.

Key points

Understanding the Pareto Principle can help you focus your time on the most important things.

The Pareto Principle shows that the relationship between inputs and outputs is generally uneven.

The Pareto Principle is not a strict law, nor is it completely mathmatically accurate.

Other UX Laws

Doherty Threshold

If a computer responds to a users input in less than 400ms, the user will take less time to make their next decision.

Doherty Threshold

Athlete waiting to start sprinting at a start line.

Hick's Law

Hick’s Law states that the more options a user is presented with, the longer it will take them to make a decision.

Hick's Law

Man looking at vending machine with many options.

Fitts's Law

Fitts's Law states that the amount of time taken to move to and select a target is a function of the distance to and size of the target.

Fitts's Law

A man aiming a bow and arrow at a far away target.