uses
psAPI;


//...

function GetProcessMemorySize(_sProcessName: string; var _nMemSize: Cardinal): Boolean;
var
l_nWndHandle, l_nProcID, l_nTmpHandle: HWND;
l_pPMC: PPROCESS_MEMORY_COUNTERS;
l_pPMCSize: Cardinal;
begin
l_nWndHandle := FindWindow(nil, PChar(_sProcessName));

if l_nWndHandle = 0 then
begin
Result := False;
Exit;
end;

l_pPMCSize := SizeOf(PROCESS_MEMORY_COUNTERS);

GetMem(l_pPMC, l_pPMCSize);
l_pPMC^.cb := l_pPMCSize;

GetWindowThreadProcessId(l_nWndHandle, @l_nProcID);
l_nTmpHandle := OpenProcess(PROCESS_ALL_ACCESS, False, l_nProcID);

if (GetProcessMemoryInfo(l_nTmpHandle, l_pPMC, l_pPMCSize)) then
_nMemSize := l_pPMC^.WorkingSetSize
else
_nMemSize := 0;

FreeMem(l_pPMC);

Result := True;
end;

//Beispiel

procedure TForm1.Button1Click(Sender: TObject);
var
l_nSize: Cardinal;
begin
if (GetProcessMemorySize('Unbenannt - Editor', l_nSize)) then
ShowMessage('Size: ' + IntToStr(l_nSize) + ' byte')
else
ShowMessage('Error');
end;