ZipArchiveEntry.Length Property

This property cannot be retrieved when the mode is set to Create, or the mode is set to Update and the entry has been opened.

The following example shows how to retrieve entries from a zip archive, and evaluate the properties of the entries. It uses the Name property to display the name of the entry, and the Length and CompressedLength properties to calculate how much the file was compressed.

using System;
using System.IO;
using System.IO.Compression;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string zipPath = @"c:\example\result.zip";

            using (ZipArchive archive = ZipFile.OpenRead(zipPath))
            {
                foreach (ZipArchiveEntry entry in archive.Entries)
                {
                    float compressedRatio = (float)entry.CompressedLength / entry.Length;
                    float reductionPercentage = 100 - (compressedRatio * 100);

                    Console.WriteLine (string.Format("File: {0}, Compressed {1:F2}%", entry.Name, reductionPercentage)); 
                }
            } 
        }
    }
}

.NET Framework

.NET for Windows Store apps

• Full trust for the immediate caller. This member cannot be used by partially trusted code. For more information, see Using Libraries from Partially Trusted Code.

Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Reference