System.Text.Encoding.GetMaxCharCount C# (CSharp) Method

        public abstract int GetMaxCharCount(int byteCount);

        private readonly StringBuilder _readLineSB; // SB that holds readLine output

        internal StdInStreamReader(Stream stream, Encoding encoding, int bufferSize) : base(stream: stream, encoding: encoding, detectEncodingFromByteOrderMarks: false, bufferSize: bufferSize, leaveOpen: true)
        {
            _unprocessedBufferToBeRead = new char[encoding.GetMaxCharCount(BytesToBeRead)];
            _startIndex = 0;
            _endIndex = 0;
            _readLineSB = new StringBuilder();
        }