How do I get a human-readable file size in bytes abbreviation using C#?

To get a human-readable file size in bytes with proper abbreviations, C# requires converting raw byte values into appropriate units like KB, MB, GB, or TB. This involves dividing by 1024 (or 1000 depending on your preference) and selecting the most appropriate unit to display.

The key is to create a method that automatically determines the best unit and formats the size accordingly, rather than showing all units simultaneously.

Syntax

To get file size in bytes −

long sizeInBytes = new FileInfo(filePath).Length;

To format the size into human-readable format −

string FormatFileSize(long bytes) {
    string[] suffixes = { "B", "KB", "MB", "GB", "TB" };
    int suffixIndex = 0;
    double size = bytes;
    
    while (size >= 1024 && suffixIndex < suffixes.Length - 1) {
        size /= 1024;
        suffixIndex++;
    }
    
    return $"{size:0.##} {suffixes[suffixIndex]}";
}

Using a Helper Method for File Size Formatting

The most efficient approach is to create a reusable method that automatically selects the appropriate unit −

using System;
using System.IO;

class Program {
    static string FormatFileSize(long bytes) {
        string[] suffixes = { "B", "KB", "MB", "GB", "TB" };
        int suffixIndex = 0;
        double size = bytes;
        
        while (size >= 1024 && suffixIndex < suffixes.Length - 1) {
            size /= 1024;
            suffixIndex++;
        }
        
        return $"{size:0.##} {suffixes[suffixIndex]}";
    }
    
    static void Main(string[] args) {
        // Create test files with different sizes
        string testFile1 = "small.txt";
        string testFile2 = "medium.txt";
        
        File.WriteAllText(testFile1, "Hello World!");
        File.WriteAllText(testFile2, new string('A', 2048576)); // ~2MB file
        
        FileInfo file1 = new FileInfo(testFile1);
        FileInfo file2 = new FileInfo(testFile2);
        
        Console.WriteLine($"File: {file1.Name}");
        Console.WriteLine($"Size: {FormatFileSize(file1.Length)}");
        Console.WriteLine();
        
        Console.WriteLine($"File: {file2.Name}");
        Console.WriteLine($"Size: {FormatFileSize(file2.Length)}");
        
        // Clean up
        File.Delete(testFile1);
        File.Delete(testFile2);
    }
}

The output of the above code is −

File: small.txt
Size: 12 B

File: medium.txt
Size: 2 MB

Processing Multiple Files with Readable Sizes

Here's how to process multiple files and display their sizes in human-readable format −

using System;
using System.IO;

class Program {
    static string FormatFileSize(long bytes) {
        if (bytes == 0) return "0 B";
        
        string[] suffixes = { "B", "KB", "MB", "GB", "TB" };
        int suffixIndex = 0;
        double size = bytes;
        
        while (size >= 1024 && suffixIndex < suffixes.Length - 1) {
            size /= 1024;
            suffixIndex++;
        }
        
        return $"{size:0.##} {suffixes[suffixIndex]}";
    }
    
    static void Main(string[] args) {
        // Create test directory and files
        string testDir = "TestFiles";
        Directory.CreateDirectory(testDir);
        
        File.WriteAllText(Path.Combine(testDir, "tiny.txt"), "Hi");
        File.WriteAllText(Path.Combine(testDir, "small.txt"), new string('A', 1024));
        File.WriteAllText(Path.Combine(testDir, "large.txt"), new string('B', 1048576));
        
        var files = Directory.GetFiles(testDir, "*.*", SearchOption.AllDirectories);
        
        Console.WriteLine("File Size Report:");
        Console.WriteLine("================");
        
        foreach (string file in files) {
            FileInfo fileInfo = new FileInfo(file);
            Console.WriteLine($"{Path.GetFileName(file)}: {FormatFileSize(fileInfo.Length)}");
        }
        
        // Clean up
        Directory.Delete(testDir, true);
    }
}

The output of the above code is −

File Size Report:
================
large.txt: 1 MB
small.txt: 1 KB
tiny.txt: 2 B

Using Decimal vs Binary Units

You can choose between binary units (1024) or decimal units (1000) based on your requirements −

using System;
using System.IO;

class Program {
    static string FormatFileSizeBinary(long bytes) {
        string[] suffixes = { "B", "KiB", "MiB", "GiB", "TiB" };
        int suffixIndex = 0;
        double size = bytes;
        
        while (size >= 1024 && suffixIndex < suffixes.Length - 1) {
            size /= 1024;
            suffixIndex++;
        }
        
        return $"{size:0.##} {suffixes[suffixIndex]}";
    }
    
    static string FormatFileSizeDecimal(long bytes) {
        string[] suffixes = { "B", "KB", "MB", "GB", "TB" };
        int suffixIndex = 0;
        double size = bytes;
        
        while (size >= 1000 && suffixIndex < suffixes.Length - 1) {
            size /= 1000;
            suffixIndex++;
        }
        
        return $"{size:0.##} {suffixes[suffixIndex]}";
    }
    
    static void Main(string[] args) {
        long fileSize = 1536000; // 1.5 MB approximately
        
        Console.WriteLine($"File size: {fileSize} bytes");
        Console.WriteLine($"Binary units: {FormatFileSizeBinary(fileSize)}");
        Console.WriteLine($"Decimal units: {FormatFileSizeDecimal(fileSize)}");
    }
}

The output of the above code is −

File size: 1536000 bytes
Binary units: 1.46 MiB
Decimal units: 1.54 MB

Comparison of Approaches

Conclusion

Converting file sizes to human-readable format in C# involves creating a helper method that automatically selects the appropriate unit (B, KB, MB, GB, TB) and formats the size accordingly. Choose between binary (1024-based) or decimal (1000-based) units depending on your specific requirements and target audience.