Fitts's Law in 2025: Button Size, Touch Targets, and Tap Accuracy

What Is Fitts's Law?

Fitts's Law, formulated by psychologist Paul Fitts in 1954, mathematically models the time required to move a pointer (or finger) to a target: T = a + b × log₂(2D/W), where D is the distance to the target and W is the target's width. The takeaway is intuitive but powerful: larger targets that are closer are faster and easier to hit.

"The time to acquire a target is a function of the distance to and size of the target."— Paul Fitts, 1954 / Laws of UX

Fitts's Law: the further away and smaller a target, the longer it takes to hit. Closer and larger = faster interaction.

Why It Still Matters in 2025

Fitts's Law was derived from physical tasks, but it maps almost perfectly onto digital interfaces — particularly touch screens, where fingertip imprecision amplifies every sizing mistake. On a 390px-wide phone screen, the difference between a 32px and 48px button is the difference between frustration and flow.

Touch Target Best Practices

• Apple HIG: Minimum 44×44pt touch target for all interactive elements.
• Google Material Design: Minimum 48×48dp with at least 8dp spacing between targets.
• WCAG 2.5.5: Recommends at least 44×44 CSS pixels for accessibility compliance.
• The visual size of a button can be smaller than its tap target — use invisible padding around small icons.

The Corner and Edge Advantage

Screen corners are infinite targets — a cursor or finger moving toward a corner can never overshoot it. This is why macOS places the Apple menu at the top-left and the Dock at the bottom. Edges are similarly forgiving in one axis. Place your most frequently used actions at screen edges or corners wherever the interaction model allows.

Practical Applications

• Primary CTAs: Make them wide (full-bleed on mobile) rather than small and centred.
• Navigation bars: Bottom nav on mobile uses the thumb's natural range — top nav forces a stretch.
• Destructive actions: Keep "Delete" and "Cancel" targets small and far from the primary action — Fitts's Law as a safety mechanism.
• Form fields: Tall input fields (48px+) reduce missed taps and improve mobile completion rates.

Key Takeaways

• Target acquisition time = function of distance + size. Larger and closer wins.
• Minimum 44×44px touch targets for every interactive element.
• Screen corners and edges are effectively infinite targets — use them for primary actions.
• Use invisible tap padding to grow touch targets without changing visual design.

References & Further Reading

• Fitts's Law — Laws of UX
• Laws of UX — Complete Reference
• Touch Target Sizing — Nielsen Norman Group