Fitts's law

The time to hit a target depends on its size and distance.

Cognitive load and fluency Applies sitewide
Where it applies

Four of the eight page areas.

HomepageNot typical CategoryNot typical SearchNot typical ProductAlso applies CartAlso applies CheckoutAlso applies Post-purchaseNot typical

It also applies sitewide, on every page. See everything at work on every page

How to use it

Four ways to put it to work.

  • Make tap targets about 1cm square on touchscreens, and never under 24 by 24 CSS pixels.
  • Use a sticky add-to-basket on mobile.
  • Keep the primary action within thumb reach.
  • Leave space between primary and destructive actions.
What the research found

A consistently confirmed model that predicts pointing speed and errors, not sales.

MacKenzie’s review reports fits that are routinely above r = .90.

One of the most consistently confirmed models in human-computer interaction. MacKenzie's review reports fits that are routinely above r = .90, and Soukoreff and MacKenzie reviewed 24 published mouse models. NN/g recommends touch targets of at least 1cm by 1cm, citing thumb-use research. The law predicts pointing speed and errors, not sales.

Key research

Five sources, each checked.

Last reviewed

Fitts (1954) The information capacity of the human motor system in controlling the amplitude of movement J. Experimental Psychology Read the source MacKenzie (1992) Fitts' law as a research and design tool in human-computer interaction Human-Computer Interaction Read the source Soukoreff & MacKenzie (2004) Towards a standard for pointing device evaluation: Perspectives on 27 years of Fitts' law research in HCI Int. J. Human-Computer Studies Read the source Harley (2019)Industry Touch Targets on Touchscreens Nielsen Norman Group Read the source Parhi, Karlson & Bederson (2006) Target size study for one-handed thumb use on small touchscreen devices MobileHCI Conference Proceedings Read the source
Before you use it · UK law

WCAG 2.2 level AA requires pointer targets of at least 24 by 24 CSS pixels, with some exceptions (44 by 44 at level AAA). The European Accessibility Act has covered ecommerce services for EU consumers since 28 June 2025, with an exemption for microenterprises, and UK service providers have a duty to make reasonable adjustments under the Equality Act 2010.

This is simply a pointer to check, not legal advice. Seek legal advice before you put this principle into action.