Fitts's law: why the size and distance of your buttons matter

The bigger and closer a target, the faster it is to reach. Obvious when put that way, yet few interfaces truly apply it. Fitts's law puts a frame around that obviousness.

Formulated by psychologist Paul Fitts in 1954, this law describes the time needed to reach a target with a pointer. Only two factors matter: the distance to travel and the size of the target. The farther or smaller the target, the slower the action and the more error-prone it is.

The principle

A large button right under the thumb is clicked instantly. A small link at the other end of the screen requires aiming, slowing down, correcting. The difference is not only speed: a target that is too small also multiplies missed clicks, and therefore frustration.

What it implies in design

• Size targets by importance. The primary action deserves the biggest button, not the most decorated.
• Bring related actions closer. A confirm button far from the field it validates is a needless trip imposed on the user.
• Respect minimum touch sizes. On mobile, a target under 44 pixels becomes hard to hit precisely.

A button is not the right size because it is beautiful, but because the hand reaches it without aiming.

Edges and corners: infinite targets

A detail Fitts's law makes precious: the screen edges and corners behave like infinitely large targets. The cursor cannot overshoot them, it stops against them. That is why system menus often sit in the corners: you reach them with a rough gesture, no precision needed. Good design uses these zones for frequent actions.

In practice

Concretely, Fitts's law guides size hierarchy, action spacing and placement of critical elements. It explains why a full-width call to action converts better than a small link, and why grouping a form's actions saves the user real time. It is one of the first laws I apply when designing an interface journey.

Frequently asked questions

What is the minimum size for a touch button?

Around 44 pixels per side is the common reference. Below that, the target becomes hard to hit precisely, especially in real mobile use.

Why are screen corners special?

Because the cursor stops against them without overshooting: they behave like infinitely large targets, and are therefore very fast to reach.

Does Fitts's law apply to touch too?

Yes. Distance becomes that of the thumb or finger, but the principle holds: big and close means fast and reliable.

Florent DABERNAT · Art director and founder of IDSEED, based in Aix-en-Provence. I help my clients with branding, UX/UI and web, using a clear and documented method. Learn more ➞