 <p>Something is missing from your question. Your input string cannot have spaces and your output of a double containing spaces is not possible.</p> <pre><code>double result = Convert.ToDouble("555 555 584", CultureInfo.InvariantCulture); </code></pre> <p>Results in:</p> <p>An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll</p> <p>Additional information: Input string was not in a correct format.</p> <p>Try this:</p> <pre><code>string value = Box.Text.Replace(" ", ""); double result = Convert.ToDouble(value, CultureInfo.InvariantCulture); </code></pre>