How to get site relative URL through PowerShell, for SPWeb?

It's easy to get server relative URL through "ServerRelativeUrl" property, for SPWeb. But how to get the site relative URL?

Below is how I get it.

$SPSiteServerRelativeUrl = $site.ServerRelativeUrl
$SPWebServerRelativeUrl = $web.ServerRelativeUrl
$SPWebSiteRelativeUrl = ""
if ($web.IsRootWeb -eq $false)
{
$SPWebSiteRelativeUrl = $SPWebServerRelativeUrl.Replace($SPSiteServerRelativeUrl + "/", "")
}
Write-Host "SPWebSiteRelativeUrl=$SPWebSiteRelativeUrl" -f DarkYellow