How to reduce iOS App Size

Mastering iOS App Optimization: A Comprehensive Guide to Reducing Size and Enhancing Performance

Vikram Kumar
6 min readApr 29, 2024

Understanding App Size Metrics:

Before embarking on the journey of reducing your iOS app’s size, it’s essential to have a clear understanding of the components contributing to its bulk. iOS app size is typically categorized into three main components:

  1. Binary Size: This refers to the compiled executable code of your app. It includes the machine code generated from your source code, along with any embedded frameworks and libraries.
  2. Resources: These encompass all the assets bundled within your app, such as images, videos, audio files, fonts, and other media resources. Resources can significantly contribute to the overall size of your app, especially if they’re not optimized or if unnecessary duplicates are included.
  3. Frameworks and Libraries: External frameworks and libraries integrated into your app also contribute to its size. While these can provide valuable functionality and streamline development, they can also add bulk if not managed efficiently.
Photo by Paul Hanaoka on Unsplash

Understanding the composition of your app’s size is crucial for prioritizing optimization efforts effectively. By identifying the largest contributors to your app’s size, you can focus on optimizing those areas to achieve the most significant reduction in size while maintaining functionality and performance.

Optimizing Images and Assets:

Images are often a primary culprit when it comes to bloating app size. To optimize images and assets effectively, consider the following techniques:

  1. Compression: Utilize image compression techniques to reduce file size without sacrificing quality. Tools like PNGCrush, ImageOptim, and Adobe Photoshop’s Save for Web feature can help reduce the size of PNGs and JPEGs.
  2. Asset Catalogs: Asset catalogs are a powerful tool for managing image assets efficiently. They allow you to organize images into sets, provide device-specific variants, and enable on-demand resource loading. By leveraging asset catalogs, you can ensure that only the necessary images are included in your app bundle, reducing its size.
  3. Vector Graphics: Whenever possible, use vector graphics (such as SVG files) for icons and UI elements instead of raster images. Vector graphics can be scaled to any size without loss of quality and typically have smaller file sizes compared to raster images.

Minimizing Resource Bundles:

Evaluate the necessity of every resource bundled with your app and remove any unused or redundant assets. Consider the following techniques to minimize resource bundles:

  1. Asset Slicing: Asset slicing allows Xcode to generate and deliver only the necessary image variants for each device at runtime. By enabling asset slicing, you can reduce the size of your app bundle by including only the image assets needed for specific device resolutions and screen sizes.
  2. On-Demand Resource Loading: On-demand resource loading enables you to defer the loading of non-essential resources until they’re needed. This can significantly reduce the initial download size of your app by excluding resources that aren’t immediately necessary for the app’s functionality.

Adopting App Thinning Techniques:

App Thinning is a set of techniques introduced by Apple to optimize the installation and execution of iOS apps. These techniques include:

  1. App Slicing: App slicing allows the App Store to deliver only the necessary resources for a particular device, reducing the download size for users. When users download your app, they receive a version that includes only the assets and resources relevant to their device configuration.
  2. Bitcode: Enabling bitcode allows Apple to re-optimize your app’s binary code for specific device architectures at compile time. This can result in smaller binary sizes and improved performance on supported devices.
  3. On-Demand Resources (ODR): With On-Demand Resources, you can package large resources (such as graphics, levels, or additional content) separately from your app bundle. These resources are then downloaded to the user’s device on-demand, reducing the initial download size of your app.

By adopting these App Thinning techniques, you can optimize your app’s size and improve the installation experience for users, especially those with limited storage space on their devices.

Evaluating Frameworks and Libraries:

Third-party frameworks and libraries can add valuable functionality to your app but may also contribute to its size. To minimize the impact of frameworks and libraries on your app’s size, consider the following:

  1. Dependency Management: Regularly review the third-party dependencies in your project and remove any unused or redundant libraries. Be mindful of the dependencies included by default when using certain frameworks or libraries, as these can add unnecessary bulk to your app.
  2. Lightweight Alternatives: Explore lightweight alternatives to popular frameworks and libraries, especially if you only require a subset of their functionality. Choosing smaller, more focused libraries can help reduce your app’s size without sacrificing functionality.
  3. Dynamic Frameworks: Whenever possible, use dynamic frameworks instead of static libraries to reduce the size of your app’s binary. Dynamic frameworks are linked to your app at runtime, allowing them to be shared among multiple apps and reducing duplication of code.

Optimizing Code:

Efficient coding practices can have a significant impact on your app’s size. Consider the following strategies to optimize your code:

  1. Code Minification: Minify your JavaScript and CSS files in iOS app development to reduce their size. This process eliminates unnecessary whitespace, comments, and redundant characters from the code, thereby leading to smaller file sizes. This optimization is crucial for enhancing app performance and ensuring faster download times, especially in hybrid app development or when utilizing web views within native iOS apps.
  2. Dead Code Elimination: Remove any dead code or unused resources from your project to reduce the size of your app’s binary. Unused code can accumulate over time as your project evolves, so it’s essential to regularly review and clean up your codebase.
  3. Optimized Asset Loading: Implement lazy loading techniques to defer the loading of non-essential assets until they’re needed. For example, you can load images and other resources asynchronously as they come into view, rather than preloading everything upfront.

Leveraging On-Demand Functionality:

Implementing on-demand functionality can help reduce the size of your app by deferring the loading of non-essential features until they’re requested by the user. This approach not only reduces the initial download size of your app but also improves its performance and responsiveness by prioritizing essential functionality.

Consider the following strategies for leveraging on-demand functionality:

  1. Feature Flags: Use feature flags or configuration files to control which features are enabled in your app. By selectively enabling features based on user preferences or device capabilities, you can reduce the overall size of your app bundle.
  2. Modularization: Break your app into modular components or modules and load them dynamically as needed. This allows you to keep the core functionality of your app lightweight while providing additional features as separate modules that can be downloaded on-demand.

Testing and Iteration:

Optimization is an iterative process, and it’s essential to test your app thoroughly on various device configurations to ensure that optimization efforts do not compromise functionality or user experience. Monitor app size metrics regularly and iterate on optimization strategies as needed to achieve the desired balance between size, performance, and user experience.

Consider the following best practices for testing and iteration:

  1. Device Testing: Test your app on a range of iOS devices, including older models with limited storage and processing power. This will help ensure that your app performs well across the entire spectrum of iOS devices and user configurations.
  2. Performance Profiling: Use performance profiling tools like Instruments to identify performance bottlenecks and areas for optimization in your app. By profiling your app’s performance, you can pinpoint areas of inefficiency and prioritize optimization efforts accordingly.
  3. User Feedback: Solicit feedback from users and incorporate their suggestions and preferences into your optimization efforts. User feedback can provide valuable insights into how your app is perceived and used in the real


In the competitive landscape of iOS app development, optimizing app size is imperative to deliver a seamless user experience. By understanding the factors contributing to app size and implementing a combination of optimization techniques such as image compression, asset management, App Thinning, and code optimization, developers can significantly reduce app size without sacrificing functionality or user experience. Embracing a culture of continuous optimization and staying abreast of emerging techniques and technologies will enable iOS developers to create lean, efficient, and user-friendly applications that resonate with modern-day users.

Happy Coding!



Vikram Kumar

I am Vikram, a Senior iOS Developer at Matellio Inc. focused on writing clean and efficient code. Complex problem-solver with an analytical and driven mindset.