I want to know how to find footprint of FreeRTOS? Thanks in advanced.

Here is a good place to start http://www.freertos.org/FAQMem.html

In manual of FreeRTOS i got information about footprint is nearly 4k. I have PC, so intel processor and BCC compiler ,i have Watcom tool where we can open project file and make, run. so based on this how can i measure footprint? Is possible in PC or i should have download some GCC based ARM cross compiler?

It will be completely different when compiled for x86 using Watcom, so there is no point compiling using GCC.  Just look at the map file output by the compiler.

In Map file size is there but it include all application size also. I want RTOS size only. That include (Source folder only) i suppose. I want that size only. i have flash in processor example ARM7. To flash it i should know size of RTOS. How can i get it?

The top of the map file contains the code size of every module.  You need to add up the size of the FreeRTOS modules.  Namely task, queue, list and port.

Is in Segment area you r telling?

That RTOS size will same for all Architecture & compiler or it could differ? I counted size from Map file ( in Segment area : segment , address , size) it is nearly 10 k. Is it right?

Why do you think it would be the same for all architectures?  Some are 8bit, some 32.  Different compilers generate different code.  Different optimizers are better than others.