Fitts' Law Calculator
Calculate target acquisition time based on distance and width
50px
1000px
px
10px
200px
px
Fitts' Law Results
Index of Difficulty (ID):
2.58
log₂(D/W + 1)
Movement Time (MT):
411
ms
a + b × ID
Visualization
Distance: 300px |
Width: 50px
Fitts' Law Formula
MT = a + b × log₂(D/W + 1)
MT = Movement Time
a = Intercept (device/input method)
b = Slope (device/input method)
D = Distance to target center
W = Width of target
ID = Index of Difficulty (bits)
About Fitts' Law
Fitts' Law is a predictive model of human movement primarily used in human-computer interaction and ergonomics. It predicts the time required to rapidly move to a target area, such as clicking a button or selecting an item from a menu.
Key Principles:
- Movement time increases with distance to the target
- Movement time decreases with target size
- The relationship is logarithmic, not linear
Applications in UX Design:
- Button and interactive element sizing
- Menu and navigation layout optimization
- Touch target sizing for mobile interfaces
- Input device comparison and evaluation
Typical Values:
| Device | a (intercept) | b (slope) |
|---|---|---|
| Mouse | 0.083 | 0.127 |
| Trackpad | 0.120 | 0.180 |
| Touchscreen | 0.150 | 0.250 |