NOTE: GOOGLE turn off currency API but now you can https://www.google.com/finance/converter?a=1&from=AUD&to=INR

Some time ago I found the following Google API , which provides the currency conversion rates for free. Maybe you’ll find it useful.
In this article, I’ll explain how to get currency rate in ASP.Net using C#.

For example, 1 AUD = ? INR (1 Australian Dollar = ? Indian Rupee )
To get INR from 1 AUD, we need to call google API in following format: ( you can try by paste this url into your web browse)

http://www.google.com/ig/calculator?hl=en&q=1AUD%3D%3FINR
The number 1 before AUD is the amount of dollars or quantity.

Above Url returns a JSON object with the details.:

{lhs: "1 Australian dollar",rhs: "47.8167309 Indian rupees",error: "",icc: true}

As you can see the result is called rhs, but it combines the resulting value with the text “Indian rupees”. Now we will remove the string and store the result as a decimal.

We implement fuction called Convert with three parameter (amount, fromCurrency, toCurrency) which return Exchange rate in decimal.

Code:

public static decimal Convert(decimal amount, string fromCurrency, string toCurrency)
        {
            WebClient web = new WebClient();
 
            string url = string.Format("http://www.google.com/ig/calculator?hl=en&q={2}{0}%3D%3F{1}", fromCurrency.ToUpper(), toCurrency.ToUpper(), amount);
 
            string response = web.DownloadString(url);
 
            Regex regex = new Regex("rhs: \\\\\\"(\\\\d*.\\\\d*)");
            Match match = regex.Match(response);
 
            decimal rate = System.Convert.ToDecimal(match.Groups[1].Value);
 
            return rate;
        }

Thanks