#C#, 85 Bytes

()=>System.Console.Write(System.Console.WindowWidth+"x"+System.Console.WindowHeight);

If you want a whole application code, we'd have 115 101 94 Bytes:

using C=System.Console;class P{static void Main()=>C.Write(C.WindowWidth+"x"+C.WindowHeight);}

However you could mean the Buffer size as well, we'd have 85 Bytes again

()=>System.Console.Write(System.Console.BufferWidth+"x"+System.Console.BufferHeight);

Or as a whole application code (obviously 115 101 94 Bytes again):

using C=System.Console;class P{static void Main()=>C.Write(C.BufferWidth+"x"+C.BufferHeight);}

Saved 14 Bytes in the whole application code with the help of Caius Jard

C#, 85 Bytes

()=>System.Console.Write(System.Console.WindowWidth+"x"+System.Console.WindowHeight);

If you want a whole application code, we'd have 115 101 94 Bytes:

using C=System.Console;class P{static void Main()=>C.Write(C.WindowWidth+"x"+C.WindowHeight);}

However you could mean the Buffer size as well, we'd have 85 Bytes again

()=>System.Console.Write(System.Console.BufferWidth+"x"+System.Console.BufferHeight);

Or as a whole application code (obviously 115 101 94 Bytes again):

using C=System.Console;class P{static void Main()=>C.Write(C.BufferWidth+"x"+C.BufferHeight);}

Saved 14 Bytes in the whole application code with the help of Caius Jard

#C#, 85 Bytes

()=>System.Console.Write(System.Console.WindowWidth+"x"+System.Console.WindowHeight);

If you want a whole application code, we'd have 115 101 94 Bytes:

using C=System.Console;class P{static void Main()=>C.Write(C.WindowWidth+"x"+C.WindowHeight);}

However you could mean the Buffer size as well, we'd have 85 Bytes again

()=>System.Console.Write(System.Console.BufferWidth+"x"+System.Console.BufferHeight);

Or as a whole application code (obviously 115 101 94 Bytes again):

using C=System.Console;class P{static void Main()=>C.Write(C.BufferWidth+"x"+C.BufferHeight);}

Saved 14 Bytes in the whole application code with the help of Caius Jard

#C#, 85 Bytes

()=>System.Console.Write(System.Console.WindowWidth+"x"+System.Console.WindowHeight);

If you want a whole application code, we'd have 115 101 94 Bytes:

using C=System.Console;class P{static void Main()=>C.Write(C.WindowWidth+"x"+C.WindowHeight);}

However you could mean the Buffer size as well, we'd have 85 Bytes again

()=>System.Console.Write(System.Console.BufferWidth+"x"+System.Console.BufferHeight);

Or as a whole application code (obviously 115 101 94 Bytes again):

using C=System.Console;class P{static void Main()=>C.Write(C.BufferWidth+"x"+C.BufferHeight);}

Saved 14 Bytes in the whole application code with the help of Caius Jard

#C#, 85 Bytes

()=>System.Console.Write(System.Console.WindowWidth+"x"+System.Console.WindowHeight);

If you want a whole application code, we'd have 115 Bytes:

using System;static class Program{static void Main()=>Console.Write(Console.WindowWidth+"x"+Console.WindowHeight);}

However you could mean the Buffer size as well, we'd have 85 Bytes again

()=>System.Console.Write(System.Console.BufferWidth+"x"+System.Console.BufferHeight);

Or as a whole application code (obviously 115 Bytes again):

using System;static class Program{static void Main()=>Console.Write(Console.BufferWidth+"x"+Console.BufferHeight);}

#C#, 85 Bytes

()=>System.Console.Write(System.Console.WindowWidth+"x"+System.Console.WindowHeight);

If you want a whole application code, we'd have 115 101 94 Bytes:

using C=System.Console;class P{static void Main()=>C.Write(C.WindowWidth+"x"+C.WindowHeight);}

However you could mean the Buffer size as well, we'd have 85 Bytes again

()=>System.Console.Write(System.Console.BufferWidth+"x"+System.Console.BufferHeight);

Or as a whole application code (obviously 115 101 94 Bytes again):

using C=System.Console;class P{static void Main()=>C.Write(C.BufferWidth+"x"+C.BufferHeight);}

Saved 14 Bytes in the whole application code with the help of Caius Jard