Don's note
Fitts's Law sounds academic; it isn't. It's the reason your phone's Home button used to be at the bottom — easy for a thumb to reach — and the reason every app with a serious conversion metric (Instagram, DoorDash, OpenTable) keeps the primary action either at the bottom of the screen or persistently visible as a floating button.
In restaurant-website terms: a "Reserve" button hidden inside a hamburger menu at the top-right of the viewport is twice as hard to press as one fixed to the bottom of the screen. Not twice as bad stylistically — twice as hard to press, measured in thumb travel. Every conversion drops proportionally. This is the cheapest UX fix a restaurant site can make, and it's the one most template builders don't do by default.
Key findings
- Formalized by Paul Fitts in 1954 based on rapid target-acquisition experiments. The finding: time-to-target is a predictable function of the distance to it and its size.
- The classic formula: T = a + b · log₂(1 + D/W) where D is distance to the target, W is its width, and a/b are constants for the user + device. Bigger targets are faster to acquire; closer targets are faster to acquire.
- Smaller buttons miss more often. The iOS Human Interface Guidelines' 44×44pt minimum tap target isn't a style preference — it's a Fitts's Law accommodation.
- Screen edges and corners are "infinite" in extent. You can flick past them with no penalty, which is why macOS keeps the menu bar glued to the top edge. Bottom-sticky mobile CTAs exploit the same property.
- Every extra tap compounds the loss. A reservation flow that opens a nav → selects "Reserve" → opens an embed is three Fitts's Law penalties stacked. Compression always wins.
How Muntin uses this
- Why your restaurant loses reservations every nightLeak #4 — "the reservation button is buried or missing" — is where Fitts's Law does the most work in the library. The sticky-bottom-CTA recommendation is Fitts's Law in practice.
- Wix vs. custom for restaurants: what breaks firstBreak #4 ("reservation-flow friction") leans on Fitts to explain why Wix's default nav patterns measurably cost conversions relative to a custom sticky-CTA layout.
Full citation
Budiu, R. Fitts's Law and Its Applications in UX. Nielsen Norman Group. nngroup.com. (Based on: Fitts, P. M. (1954). The information capacity of the human motor system in controlling the amplitude of movement. Journal of Experimental Psychology, 47(6), 381–391.)
Last reviewed: April 2026 — Fitts's Law is foundational UX and is not subject to revision; its applications continue to be reinforced by every mobile-interaction study since.