[c#] Two Radio Buttons ASP.NET C#

I have two radio buttons for metric and US measurements. I load the page so the metric radio button is clicked. How do I set the two buttons so when US is clicked metric unclicks and vise versa?

Set the GroupName property of both radio buttons to the same value. You could also try using a RadioButtonGroup, which does this for you automatically.

I can see it's an old question, if you want to put other HTML inside could use the radiobutton with GroupName propery same in all radiobuttons and in the Text property set something like an image or the html you need.

   <asp:RadioButton GroupName="group1" runat="server" ID="paypalrb" Text="<img src='https://www.paypalobjects.com/webstatic/mktg/logo/bdg_secured_by_pp_2line.png' border='0' alt='Secured by PayPal' style='width: 103px; height: 61px; padding:10px;'>" />

Make sure their GroupName properties are set to the same name:

<asp:RadioButton GroupName="MeasurementSystem" runat="server" Text="US" />
<asp:RadioButton GroupName="MeasurementSystem" runat="server" Text="Metric" />

     <asp:RadioButtonList id="RadioButtonList1" runat="server">
        <asp:ListItem Selected="True">Metric</asp:ListItem>
        <asp:ListItem>US</asp:ListItem>
     </asp:RadioButtonList>

In order to make it work, you have to set property GroupName of both radio buttons to the same value:

<asp:RadioButton id="rbMetric" runat="server" GroupName="measurementSystem"></asp:RadioButton>
<asp:RadioButton id="rbUS" runat="server" GroupName="measurementSystem"></asp:RadioButton>

Personally, I prefer to use a RadioButtonList:

<asp:RadioButtonList ID="rblMeasurementSystem" runat="server">
    <asp:ListItem Text="Metric" Value="metric" />
    <asp:ListItem Text="US" Value="us" />
</asp:RadioButtonList>