Presenting Byte Size Values in WPF, see https://thomasfreudenberg.com/archive/2017/01/21/presenting-byte-size-values-in-wpf/ for description

FormatKbSizeConverter.cs

public class FormatKbSizeConverter : IValueConverter {
    [DllImport("shlwapi.dll", CharSet = CharSet.Unicode)]
    private static extern long StrFormatByteSizeW(long qdw, [MarshalAs(UnmanagedType.LPWStr)] StringBuilder pszBuf,
        int cchBuf);

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture) {
        var number = System.Convert.ToInt64(value);
        var sb = new StringBuilder(32);
        StrFormatByteSizeW(number, sb, sb.Capacity);
        return sb.ToString();
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture) {
        return DependencyProperty.UnsetValue;
    }
}

MainWindow.xaml

<Window
  x:Class="FormatByteSizeConverterDemo.MainWindow"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
  xmlns:local="clr-namespace:FormatByteSizeConverterDemo"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  xmlns:system="clr-namespace:System;assembly=mscorlib"
  Title="MainWindow"
  Width="525"
  Height="350"
  mc:Ignorable="d">
  <Grid>
    <Grid.Resources>
      <!--  array of numbers  -->
      <x:Array x:Key="numbers" Type="system:Int64">
        <system:Int64>-1</system:Int64>
        <system:Int64>0</system:Int64>
        <system:Int64>1</system:Int64>
        <system:Int64>2</system:Int64>
        <system:Int64>532</system:Int64>
        <system:Int64>1340</system:Int64>
        <system:Int64>23506</system:Int64>
        <system:Int64>2400016</system:Int64>
        <system:Int64>2400000000</system:Int64>
        <x:Static Member="system:Int64.MaxValue" />
      </x:Array>
      <!--  the actual converter  -->
      <local:FormatKbSizeConverter x:Key="FormatKbSizeConverter" />
      <!--  style to reght-align the values in the DataGrid  -->
      <Style x:Key="RightCell" TargetType="{x:Type TextBlock}">
        <Setter Property="TextAlignment" Value="Right" />
        <Setter Property="HorizontalAlignment" Value="Stretch" />
      </Style>
    </Grid.Resources>
    <DataGrid
      AutoGenerateColumns="False"
      IsReadOnly="True"
      ItemsSource="{StaticResource numbers}">
      <DataGrid.Resources>
        <!--  the actual converter  -->
        <local:FormatKbSizeConverter x:Key="FormatKbSizeConverter" />
      </DataGrid.Resources>
      <DataGrid.Columns>
        <!--  First column shows the plain values  -->
        <DataGridTextColumn
          Binding="{Binding}"
          ElementStyle="{StaticResource RightCell}"
          Header="Plain" />
        <!--  Second column shows the formatted values  -->
        <DataGridTextColumn
          Binding="{Binding Converter={StaticResource FormatKbSizeConverter}}"
          ElementStyle="{StaticResource RightCell}"
          Header="Formatted" />
      </DataGrid.Columns>
    </DataGrid>
  </Grid>
</Window>