Video Memory size?

Use DirectDraw.

IDirectDraw7::GetCaps

dwVidMemTotal
Total amount of display memory on the device, in bytes, minus memory reserved for the primary surface and any private data structures reserved by the driver. (This value is the same as the total video memory reported by the IDirectDraw7::GetAvailableVidMem method.)
dwVidMemFree
Free display memory. This value equals the value in dwVidMemTotal, minus any memory currently allocated by the application for surfaces. Unlike the GetAvailableVidMem method, which reports the memory available for a particular type of surface (such as a texture), this value reflects the memory available for any type of surface.

or

IDirectDraw7::GetAvailableVidMem

hi,
  is there no way to get the size using only win32 api or similar without using directX?

No way as far as I know.

Use EnumDisplayDevices to get the DISPLAY_DEVICE structure, whose DeviceKey is the registy path for the device.

Under it, there is a key HardwareInformation.MemorySize. Then trying to figure out how memory size is encoded.

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