Laws of UX Explained With Examples for Product Designers

The laws of UX are a set of named principles from psychology and human-computer interaction that help designers explain and defend decisions. This guide covers the ones product designers use most, what each one means in practice, and how to avoid misusing them. Jon Yablonski's book and site, Laws of UX, collect many of these in one place.

A caution first: these are heuristics, not rules. They give you a reason to look at a problem a certain way. They do not tell you what to ship.

Laws that reduce effort

• Hick's Law. The more options you present, the longer people take to decide. Cut choices, or group them into steps.
• Fitts's Law. The time to hit a target depends on its size and distance. Make important actions larger and easier to reach.
• Jakob's Law. People spend most of their time on other products, so they expect yours to work the same way. Reuse familiar patterns unless you have a strong reason not to.
• Miller's Law. Working memory is limited. The classic figure is 7 plus or minus 2 items, though later research suggests the number is closer to four. Either way, chunk information.
• Doherty Threshold. Responses that arrive in roughly 400 milliseconds or less keep people engaged. When you cannot be that fast, show progress.

Laws of perception

• Proximity. Things placed close together read as a group. Use spacing before borders.
• Similarity. Elements that look alike read as related.
• Common Region. Elements inside a shared boundary read as a group, such as a card.
• Prägnanz. People interpret ambiguous shapes in their simplest form, so keep visuals simple.
• Von Restorff Effect. The item that differs from its neighbours is the one people remember. Use contrast for one thing per screen.

Laws of memory and motivation

• Peak-End Rule. People judge an experience mostly by its peak and its end. Polish both.
• Zeigarnik Effect. Unfinished tasks stay in memory, which is why progress indicators work.
• Serial Position Effect. People remember the first and last items in a list best.
• Aesthetic-Usability Effect. Attractive interfaces are perceived as easier to use. That earns patience, not forgiveness for a broken flow.
• Goal-Gradient Effect. Motivation rises as people get closer to a goal, so show how close they are.

Laws of complexity

• Tesler's Law. Every system has complexity that cannot be removed, only moved. Decide whether the user or the system carries it.
• Postel's Law. Be liberal in what you accept and conservative in what you send. Forgive messy input.
• Pareto Principle. Roughly 80% of effects come from 20% of causes. Find the few features that matter most.
• Parkinson's Law. Tasks expand to fill the time available. Shorter flows and autofill help.
• Occam's Razor. Among options that work, prefer the one with fewer assumptions.

How to use them without misusing them

1. Start with the user problem, then pick a law that fits it.
2. Use one law per decision. Stacking five on a screen produces a mess.
3. Treat laws as guides. They support judgment. They do not replace it.
4. Test the decision with users before you ship it.
5. Explain with evidence. In a review, cite the law and the evidence together. "Hick's Law says fewer options" is weak. "Hick's Law, and in testing people hesitated on step two" is strong.

For more on explaining design decisions, see our guide to giving and receiving design critique.