The UX laws and principles behind good design

A plain-English guide to the laws of UX and the UI UX design principles behind them: Hick's Law, Fitts's Law, the Gestalt principles and more, with examples.

What are the laws of UX?

The laws of UX are research-backed principles of UI UX design, about how people perceive, decide and act on interfaces: Hick's Law on choices, Fitts's Law on targets, Miller's Law on memory, the Doherty Threshold on speed, and more. They are rules of thumb, not commandments, so each page here says when a law applies and when it doesn't.

Browse by topic, or jump straight into a challenge: every law is practised on a real product decision inside UX Quest.

Decisions and cognitive load

How many choices people can handle, how much they can hold in mind, and how fast they reach value. Start here if screens feel overwhelming.

Hick's Law — Decision time grows logarithmically with the number and complexity of choices.
Miller's Law — People hold ~7±2 items in working memory. Surface the few that matter.
Information Architecture — Group by user task, not org chart. Limit top-level to ~7 items.
Jakob's Law — Users spend most of their time on other sites, so they expect yours to work the same way as the ones they already know.
Tesler's Law — Every system has an amount of complexity that cannot be removed, only moved.
Density Matches Context — Density should match the user's task — consumer apps breathe, pro tools pack.
Time-to-Value — The faster a user reaches their first valuable outcome, the higher the activation.
Endowed Progress Effect — People work harder to finish a goal when they are already part of the way there.
Goal Gradient Effect — The closer people get to a goal, the harder they work to reach it.
Interruption Cost — Unsolicited modals break flow and erode trust. Reserve them for irreversible decisions.

Speed, feedback and states

What users see while the system works, fails or has nothing to show. Interfaces feel trustworthy when every moment is designed.

Doherty Threshold — Productivity soars when a system responds within 400ms. Below that, interaction feels instant.
Design every state — Loading, empty, error and success each need a deliberate design.
Postel's Law — Be liberal in what you accept and conservative in what you send.

Touch targets and reach

Size and distance decide whether a tap lands. The rules for buttons, icons and thumbs on real phones.

Fitts's Law — Time to acquire a target depends on its distance and size. Bigger + closer = faster.
Minimum tap target — Touch targets should be at least 44×44pt.
Touch-Target Sizing — Apple HIG: ≥44×44pt. Material: ≥48dp. Padding determines both feel and tappability.
WCAG 2.5.5 Target Size — Touch targets should be at least 44×44 CSS pixels with adequate spacing.

Gestalt: how we see groups and shapes

How people group, complete and simplify what they see: proximity, common region, continuity, closure and Pragnanz.

Law of Proximity — Objects near each other are perceived as a group. Spacing communicates relationship.
Law of Similarity — Things that look alike are seen as belonging together, or as doing the same thing.
Law of Common Region — Elements inside the same enclosed area are seen as a group.
Law of Continuity — The eye follows a smooth line or path and prefers continuous shapes over broken ones.
Law of Closure — The eye fills in small gaps to see a complete, whole shape.
Law of Pragnanz — People see ambiguous or complex scenes in the simplest form they can.

Visual design and layout

Hierarchy, grouping, alignment, colour, spacing and type: the principles that make a screen read at a glance.

Visual hierarchy — The most important text should look the most important.
Von Restorff Effect — When several similar items are shown together, the one that differs is the one remembered.
Alignment Principle — Aligned elements feel intentional and reduce cognitive load. Stray edges feel sloppy.
Aesthetic-Usability Effect — Users perceive aesthetic designs as more usable, but aesthetics alone won't carry a confused user.
60-30-10 Rule — 60% dominant (neutral), 30% secondary, 10% accent. Ratios create visual calm.
Modular Type Scale — A geometric scale (e.g. 1.25× or 1.333×) gives proportional jumps the eye can parse.
8-pt Spacing Scale — A multiple-of-8 (or 4) scale gives consistent rhythm and predictable layouts.
Token Layering — Primitive tokens hold raw values; semantic tokens map them to roles. Themes swap semantics.

Accessibility

Contrast ratios, target sizes and the measurable rules behind most accessibility wins.

Accessible contrast — Text needs ≥ 4.5:1 against its background (3:1 for large text / UI).
WCAG 1.4.3 Contrast — Normal text needs 4.5:1, large text 3:1. Aim for AAA (7:1) on body when feasible.
WCAG baselines — A few measurable rules cover most accessibility wins.

Research, testing and conversion

How many users to test, how to run an experiment you can trust, and where to fix a funnel first.

Nielsen's 5-User Rule — 5 users uncover ~85% of usability issues. More users find the same problems repeatedly.
Single-Variable Testing — Change one variable per arm so the winner is attributable. Otherwise it's a guess.
Statistical Power — Test duration depends on traffic, baseline rate, and minimum detectable effect.
Funnel Triage — Optimize the biggest leak first. Conversion math compounds — fixing 48pt beats fixing 4pt.

AI trust and specificity

Designing AI features people can rely on: when to trust, verify or override, and how specific an answer should be.

Calibrated Trust — Show users when to trust, verify, and override AI output.
Specificity Principle — AI outputs match the specificity of the input.

Guides

Heuristic evaluation: how to run one in an afternoon — Six steps, a severity scale and a worked example, plus when it is the wrong tool.
Nielsen's 10 usability heuristics, with a real example of each — Each one explained with an example, and the UX law behind it.
UX audit: what it is and how to run one, with a checklist — Seven steps, a checklist you can copy and a worked example, plus where audits fall short.
UX case study: how to write one that shows your thinking — A structure, a worked example, and how to present it, built around the decisions you made.
Bad UX examples: 10 common mistakes and how to fix them — Real screens with the mistake in them, the law that explains it, and what to do instead.
AI product design: 8 principles for AI features people trust — Set expectations, show how sure it is, keep people in control, and design the failures.
Gestalt principles: the laws of grouping, with UX examples — The laws of grouping, each with a real interface example and the mistake it prevents.
UX basics: what UX design is, how it works, and where to start — What UX design is, UX vs UI, the process, the principles, and how to start practising.