Return total records from SQL Server when using ROW_NUMBER

I would like to return the total number of records in the database so I can set up pagination. How do I return the total number of records in the DB when using the following paging method in SQL Server 2008?

    ALTER PROCEDURE [dbo].[Nop_LoadAllOptimized]
    (
        @PageSize int = 20,
        @PageNumber int = 1,
        @WarehouseCombinationID int = 1,
        @CategoryId int = 58,
        @OrderBy int = 0,
        @TotalRecords int = null OUTPUT
    )
    AS
    BEGIN
    WITH Paging AS (
        SELECT rn = (ROW_NUMBER() OVER (
        ORDER BY 
            CASE WHEN @OrderBy = 0 AND @CategoryID IS NOT NULL AND @CategoryID > 0
            THEN pcm.DisplayOrder END ASC,
            CASE WHEN @OrderBy = 0
            THEN p.[Name] END ASC,
            CASE WHEN @OrderBy = 5
            THEN p.[Name] END ASC,
            CASE WHEN @OrderBy = 10
            THEN wpv.Price END ASC,
            CASE WHEN @OrderBy = 15
            THEN wpv.Price END DESC,
            CASE WHEN @OrderBy = 20
            THEN wpv.Price END DESC,
            CASE WHEN @OrderBy = 25
            THEN wpv.UnitPrice END ASC  
        )), p.*, pcm.DisplayOrder, wpv.Price, wpv.UnitPrice FROM Nop_Product p
        INNER JOIN Nop_Product_Category_Mapping pcm ON p.ProductID=pcm.ProductID
        INNER JOIN Nop_ProductVariant pv ON p.ProductID = pv.ProductID
        INNER JOIN Nop_ProductVariant_Warehouse_Mapping wpv ON pv.ProductVariantID = wpv.ProductVariantID
        WHERE pcm.CategoryID = @CategoryId AND (wpv.Published = 1 AND pv.Published = 1 AND p.Published = 1 AND p.Deleted = 0)
        AND wpv.WarehouseID IN (select WarehouseID from Nop_WarehouseCombination where UserWarehouseCombinationID = @WarehouseCombinationID)    
    )
    SELECT TOP (@PageSize) * FROM Paging PG
    WHERE PG.rn > (@PageNumber * @PageSize) - @PageSize 

    SET @TotalRecords = @@ROWCOUNT 

    END

I typically do it this way - never really checked whether it's very efficient from a performance point of view:

WITH YourCTE AS 
(
   SELECT 
       (list of columns),
       ROW_NUMBER() OVER (ORDER BY ......) AS 'RowNum' 
   FROM dbo.YourBaseTable
)
SELECT 
    *,
    (SELECT MAX(RowNum) FROM YourCTE) AS 'TotalRows' 
FROM 
    YourCTE
WHERE   
    RowNum BETWEEN 101 AND 150

Basically, the RowNum value will have values 1 through the total of rows (if you don't have a PARTITION BY in your CTE) and thus selecting MAX(RowNum), you get the total number of rows.