Mobile App Design: Understanding Screen Sizes and Pixels

Mobile app design requires careful consideration of screen sizes and pixel densities across different devices. This comprehensive guide will help you understand the key concepts and measurements needed for effective mobile app development.

Physical vs. Logical Pixels

In mobile app development, there are two important types of pixels to consider:

Physical pixels (device pixels) are the actual pixels on the screen hardware. For example, an iPhone 13 has 2532 × 1170 physical pixels.

Logical pixels (points/dp) are the abstract units used in app development that get scaled to physical pixels. iOS uses points, while Android uses density-independent pixels (dp).

Common Screen Sizes

iOS Devices

• iPhone SE (2nd gen): 375 × 667 points
• iPhone 13 Mini: 375 × 812 points
• iPhone 13/13 Pro: 390 × 844 points
• iPhone 13 Pro Max: 428 × 926 points
• iPad Mini: 768 × 1024 points
• iPad Pro 12.9″: 1024 × 1366 points

Android Devices

• Small phones: 360 × 640 dp
• Medium phones: 360 × 720 dp
• Large phones: 411 × 731 dp
• Tablets: 768 × 1024 dp

Device Pixel Ratio (DPR)

DPR indicates how many physical pixels represent one logical pixel:

• iPhone 13: 3x (1 point = 3 physical pixels)
• Many Android flagships: 3x or higher
• Budget Android phones: 2x
• Older devices: 1x

Design Recommendations

1. Start with standard breakpoints: Small phones: 320-360 logical pixels width Large phones: 360-480 logical pixels width Tablets: 768+ logical pixels width
2. Use responsive design practices:
   • Employ flexible grids
   • Make touch targets at least 44×44 points/dp
   • Allow text to wrap naturally
   • Use relative units rather than fixed pixels
3. Account for safe areas:
   • iOS notches: ~44pt from top
   • Navigation bars: ~44-48pt
   • Tab bars: ~49pt
   • Status bar: ~20pt
4. Support multiple pixel densities:
   • Provide @2x and @3x assets for iOS
   • Use Android’s various density buckets (mdpi, hdpi, xhdpi, xxhdpi)
   • Consider using vector assets when possible

Testing Recommendations

Test your app design on:

• Different physical device sizes
• Various pixel densities
• Both portrait and landscape orientations
• Different OS versions
• Different manufacturer customizations (for Android)

Common Pitfalls to Avoid

1. Designing only for one screen size
2. Using fixed pixel values instead of relative units
3. Ignoring safe areas and system UI elements
4. Not accounting for text size accessibility settings
5. Assuming all devices have the same pixel density

Future Considerations

As mobile technology evolves, consider:

• Foldable displays
• Variable refresh rates
• Dynamic notch sizes
• Curved and waterfall displays
• Under-display cameras

Understanding these pixel-related concepts is crucial for creating responsive, accessible, and future-proof mobile applications that work well across the diverse ecosystem of mobile devices.