CtrEditor/ObjetosSim/UserControls/ucBotella.xaml

<UserControl x:Class="CtrEditor.ObjetosSim.ucBotella"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:convert="clr-namespace:CtrEditor.Convertidores">
    <UserControl.Resources>
        <convert:MeterToPixelConverter x:Key="MeterToPixelConverter"/>
    </UserControl.Resources>
    <Ellipse Height="{Binding Diametro, Converter={StaticResource MeterToPixelConverter}}"
             Stroke="red" Fill="Gray"
             Width="{Binding Diametro, Converter={StaticResource MeterToPixelConverter}}"/>

</UserControl>