windows - How to create a new volume with free space

I tried googling it but I couldn't find any answers so I thought I'll ask it here.
I've got a harddrive with a lot of free space and 1 primary partition but every time I click new simple volume and set a size for the volume which is below the size of the free space it says: There is not enough space available on the disk(s) to complete the operation.
Any idea why?