I got the below answer from StackExchange and it did the job.
if you have access to powershell then use this
#Get the Site collection
$Site = Get-SPsite "http://sharepoint.crescent.com"
#Returns a DataTable similar to "Storage Management Page" in Site settings
$DataTable = $Site.StorageManagementInformation(2,0x11,0,10)
$DataTable | Select Title, ItemCount, Size, Directory | Format-Table
Get SharePoint Library Size with PowerShell[
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