The 30 laws that fix 80% of interface problems. Hick's, Fitts's, Miller's, and more.
The 30 laws that fix 80% of interface problems. Hick's Law tells you how many options to show. Fitts's Law sizes your buttons. Miller's Law structures your navigation. These aren't opinions—they're peer-reviewed formulas used by Stripe, Linear, and Notion. Apply them and watch conversion rates, task completion, and user satisfaction metrics improve.
Key Concepts:
Key Concepts:
How these principles validate your work—whether you use Figma, Cursor, or V0
Stop reinventing the wheel. Hick's Law tells you exactly how many options to show. Fitts's Law sizes your buttons. These 30 principles are the shortcuts top designers use—memorize them and you'll solve interface problems in minutes, not meetings.
Vague specs cost you time. When a PM says "make it more intuitive," these principles translate that into concrete implementation: reduce choices, increase target sizes, add system status feedback. Build to spec the first time instead of iterating through subjective feedback cycles.
"Users don't convert" isn't a diagnosis. These principles pinpoint the exact cause: "Form abandonment at step 3 due to Hick's Law violation—too many payment options." Turn mystery metrics into actionable fixes with principles that have been validated across millions of users.
35 principles organized into 2 chapters
16 principles
14 principles
Validation paths tailored for different experience levels
From Subjective to Scientific
Master the "Big Five" first: Consistency, Visibility, Feedback, Error Prevention, and User Control. These principles apply to every screen you'll ever design. Audit one of your current projects against these five—you'll find issues immediately.
From Guesswork to Guidelines
Study how principle violations compound. A button that violates Fitts's Law AND lacks proper feedback fails twice as hard. Learn to stack principles for maximum impact and identify which violations are causing your metrics to suffer.
From Features to Outcomes
Run heuristic evaluations using all 30 principles as your framework. Lead design reviews that catch issues before development. When principles conflict (consistency vs. innovation), know how to make the call and document the tradeoff.
Validate your AI output with these principles in your daily workflow
Run a 30-principle audit on your highest-traffic page:
Build these principles into your process:
Apply what you learned with these exercises
Evaluate your current product against all 30 principles
Identify which principles are most critical for your context
Compare how competitors implement these principles
Document improvements when applying core principles
Use these principles as a structured review checklist
Recommended knowledge before starting
While you can start here, understanding the psychological principles from Part I will deepen your comprehension of why these core principles work.