There are several reasons why fonts may appear differently on various devices. These factors include:
Operating System Rendering: Different operating systems use distinct font rendering engines, which influence how fonts are displayed. For instance, Windows uses ClearType, while macOS employs subpixel anti-aliasing, leading to variances in sharpness and smoothness.
Resolution and Display Technology: Devices differ in screen resolution and pixel density (DPI or PPI), impacting how fonts scale and appear. High-resolution displays often render text more crisply than low-resolution ones.
Font Type and Availability: Not all devices have the same fonts installed. If a specific font isn’t available, a substitute font may be used, altering the design. Differences between web-safe fonts and custom fonts can also affect consistency.
Browser and Software Variations: Browsers have unique ways of handling font display, including differences in CSS rendering and font smoothing techniques. Similarly, software and apps can have predefined settings influencing text appearance.
Font Hinting and Anti-Aliasing: Hinting refers to the process of adjusting the font display to enhance its appearance on digital screens. Anti-aliasing smoothens the edges of fonts. Variations in these processes between devices can alter font aesthetics.
User Settings and Preferences: Users may adjust settings such as zoom levels, accessibility features, and screen adjustments (brightness, contrast), affecting font visibility and presentation.

Understanding these factors can help in anticipating why fonts might look different and in making design choices that ensure better cross-device compatibility.