Minimize distance to high-frequency targets.
Place commonly used controls within short motor reach.
Contents 3. Interaction Mechanics & Agency 6. Fitts’s Law
The governing physical constraint on all interaction.
First, ask yourself
“Are frequent or critical targets in your system fast and easy to acquire physically?”
Mission statement
Ensure users can target actions easily by optimizing size and distance of interactive elements.
Key heuristics Fitts’s Law
- High-frequency targets must be placed within short motor reach.
- Target size must correspond to usage frequency and consequence.
- Routine or low-risk actions must not demand fine motor accuracy.
- Screen boundaries must be leveraged for frequent or critical actions.
- High-value actions must be the easiest to acquire.
- Unnecessary target acquisitions must be eliminated.
- Layout must prioritize motor efficiency over visual symmetry alone.
- Target design must account for device-specific motor constraints.
- Design must reduce repeated acquisition costs during sustained use.
- Motor performance principles must inform layout before testing.
Executive brief
Interaction speed is constrained by physical targeting, not just system performance.
Core questions Fitts’s Law
“Is the physical effort to interact minimized?”
“Is slowness due to user movement and precision, not system lag?”
Focus areas
Motor-control focused
“How far must the user move? How precise must they be?”
“Do routine actions demand unnecessary precision?”
Workflow-aware
“How many target acquisitions does the task require?”
“Which targets dominate the time cost of the workflow?”
Device-agnostic
“Does the interaction respect human motor limits across devices?”
“Would it feel slow on any input method?”
AI-aware
“Can AI assist by reducing required movement or precision?”
“Does automation make interaction smoother without adding cognitive load?”
UX directives Fitts’s Law
Size interactive targets according to frequency and consequence.
Make important or frequent actions larger and easier to acquire.
Avoid unnecessary precision requirements.
Do not require fine motor accuracy for routine or low-risk actions.
Use screen edges strategically for frequent or critical actions.
Leverage boundaries to reduce motor effort.
Align target accessibility with usage frequency and importance.
Ensure high-value actions are easiest to acquire.
Reduce unnecessary target acquisitions.
Eliminate redundant steps to decrease total motor effort.
Prioritize motor efficiency over visual symmetry.
Design layouts according to acquisition performance, not aesthetic balance alone.
Adapt target design to input modality.
Account for device-specific motor constraints in layout and sizing decisions.
Optimize for cumulative motor efficiency.
Design to reduce repeated acquisition costs during sustained use.
Apply motor performance principles proactively.
Use Fitts’s Law to inform design decisions before usability testing.
Executive summary
- Fitts’s Law governs motor effort, not visual arrangement.
- It predicts movement time from target distance and width; accuracy enters through the speed–accuracy trade-off.
- The system must make frequent and high-value actions largest and easiest to acquire.
- Design must reduce unnecessary precision and redundant target acquisition.
- Motor efficiency must take precedence over aesthetic symmetry and arbitrary layout decisions.
- Fitts’s Law succeeds when repeated interaction minimizes cumulative motor effort over sustained use.
Success indicators
- Frequently used controls are easy to reach.
- Important actions have larger and easier targets.
- Routine actions do not require precise pointing.
- High-value actions are placed close to where users interact.
- Users can perform repeated actions quickly and comfortably.
One-line summary
Before interaction can feel fast, physical effort must be respected.