When we are running sandbox solutions in our SharePoint environment (SharePoint 2010/2013/Online), the current usage is measured by the resource measure settings of the user code service. Detailed information is available in Technet: Resource Usage Limits on Sandboxed Solutions in SharePoint 2010

To get the current resource measure settings in the farm, we can use a simple PowerShell snippet:

([Microsoft.SharePoint.Administration.SPUserCodeService]::Local).ResourceMeasures | ft Name, MinimumThreshold, ResourcesPerPoint, AbsoluteLimit

Here we have a sample output, when we run the script:

Retreiving this information via PowerShell is not available vor SharePoint Online (Office 365).