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Plate LAW·002 · LawGrid A2 · Rev. 2026-08-14

Fitts's Law

Time to hit a target depends on how far away it is and how big it is, which makes size and distance the two levers you control.

LawEstablished researchFoundational

Definition

Fitts's Law models pointing as a speed-accuracy trade-off. Movement time increases with the distance to a target and decreases with the target's size along the axis of motion: MT = a + b·log₂(2D / W). The log term is the index of difficulty, measured in bits.

Established research. Originates in published research and has been replicated. The effect is real. Its size in your product still needs measuring.

On this plate
  1. 1Definition
  2. 2One of the most robust findings in HCI
  3. 3Practical consequences
  4. 4Minimum target sizes in published guidance
  5. 5Sizing and placing targets
  6. 6In practice
  7. 7Commonly confused with
  8. 8Local chart
  9. 9Sources
  10. 10Continue from here

Reach for this when

  • Designing any touch or pointer target.
  • Deciding where to place a frequently repeated action.
  • Auditing mis-tap or rage-tap analytics.

Common mistakes

  • Sizing the icon rather than the hit area.
  • Placing a destructive action adjacent to a frequent one.
  • Assuming a hover-only affordance survives on touch, where there is no pointer position to be near.
  • Treating the law as a rule about size alone, when distance is the other half of it.

One of the most robust findings in HCI

Paul Fitts published the original work in 1954 using a stylus-tapping task. The relationship has since held across mice, trackpads, touchscreens, styluses, eye gaze and foot pedals. Scott MacKenzie's 1992 Shannon formulation is the version most commonly used today because it behaves better at low indices of difficulty.

For designers the useful reduction is simple: make important targets bigger, put them closer to where the pointer already is, and exploit the edges of the screen.

pointerdistance Dnarrow W: slowersame distance Dwide W: faster
Distance and width both feed the index of difficulty. Widening a target along the direction of travel helps more than widening it across that direction.

Practical consequences

  • Screen edges and corners behave as infinitely deep targets, because the pointer cannot overshoot past them. This is why the macOS menu bar at the top edge is faster than a menu bar inside a window.
  • The clickable area matters, not the visible area. A 16px icon inside a 44px hit area obeys the 44px.
  • Radio buttons and checkboxes should have their labels inside the target. Doing so often triples the effective width for free.
  • Contextual menus that open at the pointer beat fixed toolbars for repeated actions, because D approaches zero.
  • Destructive actions benefit from being small and far away, which is the law applied in reverse.

Minimum target sizes in published guidance

These are guidance figures from platform vendors and the WCAG standard, not outputs of the equation. They are floors, not targets to aim for.

SourceMinimumNotes
WCAG 2.2, Target Size (Minimum), AA24 × 24 CSS pxSuccess criterion 2.5.8. Exceptions exist for inline links and user-agent controls.
WCAG 2.1, Target Size (Enhanced), AAA44 × 44 CSS pxSuccess criterion 2.5.5.
Apple Human Interface Guidelines44 × 44 ptLong-standing iOS guidance.
Material Design48 × 48 dpWith at least 8dp of spacing between targets.

Sizing and placing targets

Do

  • Extend the hit area past the visible control, so small icons stay easy to hit.
  • Put frequent actions where the thumb already is, and rare ones further away.
  • Use the screen edges for persistent controls. An edge is effectively an infinitely deep target.
  • Make the whole row or card clickable when the whole row means one thing.

Do not

  • Place a destructive action adjacent to the one people use constantly.
  • Rely on a four-pixel drag handle as the only way to perform an action.
  • Put a primary action in the top corner of a large phone.
  • Shrink targets to fit more in, then add spacing to compensate. The size is the lever.

In practice

  1. i.

    The bottom bar on mobile

    Mobile app navigation

    Primary navigation moved from the top of phone screens to the bottom because the thumb rests near the bottom edge. Distance dropped for the most frequent action in the app, and the bottom edge adds an effective backstop.

  2. ii.

    Full-row list targets

    Settings and lists

    Making the whole row tappable rather than only the chevron increases target width by an order of magnitude at zero visual cost, and removes the most common source of mis-taps in settings screens.

  3. iii.

    Delete beside Save

    Distance as safety

    Two adjacent buttons of equal size are equally easy to hit, which is the problem. Separation, a different weight, or a confirmation for one of them is the design response, and separation is the cheapest.

Commonly confused with

Close neighbours that get substituted for each other. The difference is stated first, then the condition that picks one over the other.

vs.

Steering Law

Law

Time to move along a constrained path rises with its length divided by its width.

Key difference

Fitts's Law is about acquiring a target: distance and size decide how long the pointer takes to arrive. Steering is about staying inside a path on the way there. A submenu is easy to reach and hard to steer into, which is why it fails.

Use Fitts's Law when

  • The movement ends in a click on a discrete target.
  • The levers are how big the control is and how far it sits.
  • Screen edges and corners are in play, being effectively infinite.

Use Steering Law when

  • The pointer has to stay inside a corridor, as in a nested menu.
  • Leaving the path cancels or changes what is happening.
  • The fix is a wider path, a shorter one, or a forgiving timeout.

Learn about Steering Law

Local chart

LAW·002 · Region I · Grid A2

This entry and the entries it is stated to connect with. Each line is labelled with what the connection means.

Target SizeA11Y·011 · EXPLAINSButtonCMP·001 · APPLIED THROUGHCheckboxCMP·005 · APPLIED THROUGHPaginationCMP·021 · APPLIED THROUGHSliderCMP·008 · APPLIED THROUGHDestructive ActionsPAT·009 · APPLIED THROUGHMobile Interaction PatternsPAT·027 · APPLIED THROUGHNavigationPAT·001 · APPLIED THROUGHAdaptive LayoutFND·044 · APPLIED THROUGHDensityFND·016 · APPLIED THROUGHSpacing SystemsFND·042 · APPLIED THROUGHSteering LawLAW·016 · COMMONLY CONFUSED WITH

Sources

Where a source establishes something narrower than the popular reading of it, the note says so.

  1. [1]

    The information capacity of the human motor system in controlling the amplitude of movement

    P. M. Fitts, Journal of Experimental Psychology, 1954

  2. [2]

    Fitts' law as a research and design tool in human-computer interaction

    I. S. MacKenzie, Human-Computer Interaction, 1992

    Introduces the Shannon formulation used in most modern HCI work.

  3. [3]

Continue from here

Each link says what the connection is, so you can tell a principle from an alternative from a thing people mix this up with.

Applies when you are designing

A Data TableA Mobile AppAn Enterprise WorkflowNavigation

Explains

The mechanism underneath these entries.

  • Target SizeA11Y·011 · Accessibility

    The WCAG minimum is the accessibility floor under an effect that is really about distance and size together.

Applied through

Where this shows up as a concrete interface decision.

Check your work

Review passes that test whether this was done properly.

Related concept

Connected closely enough to change how you apply this.