As we use PERFMON – Performance Monitor to identify real time happening on SQL Server, Here using a DMV “sys.dm_os_performance_counters” may be used to calculate number of transactions on SQL Server as

DECLARE @Counter bigint

SELECT @Counter = cntr_value FROM sys.dm_os_performance_counters
WHERE counter_name = 'Transactions/sec'
AND object_name = 'SQLServer:Databases'
AND instance_name = 'Test'   -- Your DB Name

-- Wait for 1 second
WAITFOR DELAY '00:00:01'

SELECT
cntr_value - @Counter FROM sys.dm_os_performance_counters
WHERE counter_name = 'Transactions/sec'
AND object_name = 'SQLServer:Databases'
AND instance_name = 'Test'   -- Your DB Name