Fitts' Law Test: Measure Pointing Accuracy

This game measures mouse movement and needs a real pointer cursor. On a touchscreen, come back with a mouse or trackpad.

Leaderboard

Fast clicking puts strain on your wrist and fingers, so take a short break between rounds.

What Fitts' law explains

Fitts' law describes how long a pointing movement to a target takes: movement time grows with distance and shrinks with target width, summarized in the index of difficulty ID = log2(D/W + 1). The test runs through twelve distance-width combinations and fits a regression line MT = a + b·ID to your actual movement times, then derives throughput in bit/s from it.

Why effective target width matters

The nominal target width W says little about how precisely you actually click. This test instead follows the ISO 9241-9 method and uses the effective target width We = 4.133 · SD of your click spread around the target center, not the drawn circle size. That is the difference to many simple clones, which only use the Shannon formulation and the nominal width, allowing arbitrarily high scores no matter how inaccurate the clicking is.

What throughput says about your mouse and ergonomics

A higher throughput means distance and target size cost you less time than average, a useful comparison across input devices, DPI settings, or mouse versus trackpad. Values between 3.7 and 4.9 bit/s are typical for a computer mouse under normal use.

Frequently asked questions

Answers to common questions about the Fitts' law test

A law of motion described by Paul Fitts in 1954: the farther away and the smaller a target, the longer a pointing movement to it takes. The formula ID = log2(D/W + 1) combines distance D and target width W into a single difficulty score that predicts movement time.

For a computer mouse, 3.7 to 4.9 bit/s is the usual range, and practiced users score even higher. Touchpads and trackballs tend to fall below that. The score depends heavily on the input device, DPI setting, and practice, so a single run is more of a snapshot than a final verdict.

The ISO 9241-9 standard calls for several distance-width pairs so the regression MT = a + b·ID stays reliable across a wide difficulty range. This test uses three distances (150, 300, 600 px) and four target widths (12, 24, 48, 96 px), giving twelve combinations, and shuffles their order randomly so no learning effect skews the result in one direction.

Effective target width We replaces the drawn circle size with a measure of your actual accuracy: We = 4.133 times the standard deviation of your clicks around the target center. Click consistently and We stays small, raising throughput; scattered, inaccurate clicks lower it even at the same target size.

Yes, directly. Resolution, DPI setting, pointer acceleration, and even the mouse pad affect how long a pointing movement takes and how accurately it lands. Changing any of these between two runs limits how comparable the scores are, so use the same hardware and settings for a fair comparison.

Measuring Fitts' law: what the test does

Fitts' law is one of the best-established laws in human-computer interaction: it predicts how long a pointing movement to a target takes, based on the distance to the target and its width. This test implements the ISO 9241-9 method, the industry standard for measuring pointing devices, and produces a single comparison score at the end: throughput in bit/s.

What the test is used for

Comparing input devices: Mouse versus trackpad, different DPI settings, or a new mouse against the old one: throughput turns the difference into a single number.
Ergonomics check: A noticeably lower throughput than usual can point to fatigue, an awkward hand position, or a problem with the input device.
A reference for UI research: Anyone working with Fitts' law themselves gets a working ISO 9241-9 reference implementation here, including regression and effective target width.

How a run works

1 Two circles appear at distance D, one highlighted in fuchsia as the active target.
2 Click the active target. The first hit starts the round, every further hit switches the active target.
3 Ten scored hits per combination, then the next of twelve shuffled distance-width combinations follows automatically.
4 After all twelve rounds, throughput, the regression line, and the scatter plot appear.

What sets this test apart from simple clones

Many Fitts' law tests only use the nominal target width and the plain Shannon formulation, which allows arbitrarily high scores no matter how inaccurate the clicking is. This test instead follows the ISO 9241-9 method: it derives the effective target width from your actual click spread and uses that to compute throughput. When submitting to the leaderboard, the browser also sends the complete click and target trace, and the server recomputes the regression and throughput independently.

Free tools that pair well with this one – right in your browser, no sign-up.

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Fitts' Law Test