C# - SI prefixes for metric units - because size matters

Sometimes you will have to play with numbers, BIG numbers… Or teeny-tiny ones! To avoid having too many zeros you can use the SI prefixes (like metric units: mm, cm, m, km, …).

Here are the results of our code:

            123,460000 ->       123,460  w (1000)
            123,460000 ->       123,460  w (1024)
          1.234,560000 ->         1,235 kw (1000)
          1.234,560000 ->         1,206 kw (1024)
        123.456,000000 ->       123,456 kw (1000)
        123.456,000000 ->       120,563 kw (1024)
      1.234.567,000000 ->         1,235 Mw (1000)
      1.234.567,000000 ->         1,177 Mw (1024)
     12.345.678,000000 ->        12,346 Mw (1000)
     12.345.678,000000 ->        11,774 Mw (1024)
              0,012300 ->        12,300 mw (1000)
              0,012300 ->        12,595 mw (1024)
              0,000012 ->        12,300 µw (1000)
              0,000012 ->        12,897 µw (1024)

And here is the helper:

static void Main(string[] args)
{
    var unit = "w"; // To denote we are measuring "wathever"

    foreach (var example in new[] { 123.46, 1234.56, 123456, 1234567, 12345678, 0.0123, 0.0000123 })
    {
        foreach (var groupWeight in new[] { 1000 /* Decimal*/, 1024 /* Binary */ })
        {
            Console.WriteLine("{0,22:#,##0.000000} -> {1,16} ({2,4})",
                example, Format(example, unit, groupWeight), groupWeight);
        }
    }
    Console.ReadLine();
}

static string Format(
    double number, 
    string unitSymbol, 
    int groupWeight = 1000,
    string unitMultipliers = " kMGT",
        string unitDivider = " mµnp")
    {
        string formatted = null;
        var numberWeigth = (int)Math.Floor(Math.Log(number) / Math.Log(groupWeight));
        Nullable<char> unitWeigthSymbol = null;

        if (numberWeigth > 0)
        {
            numberWeigth = Math.Min(numberWeigth, unitMultipliers.Length - 1);
            unitWeigthSymbol = unitMultipliers[numberWeigth];
        }
        else
        {
            numberWeigth = -Math.Min(Math.Abs(numberWeigth), unitDivider.Length - 1);
            unitWeigthSymbol = unitDivider[-numberWeigth];
        }

        number = number / Math.Pow(groupWeight, numberWeigth);
        formatted = string.Format("{0:0.000} {1}{2}", number, unitWeigthSymbol, unitSymbol);

        return (formatted);
    }
}

Now if you need to specify the decimal separator as a dot or as a coma, please have a look at this article.

Happy coding^9 ! 😉