Formatting a number with a metric prefix? [duplicate]

Answer 1

Try this out. I haven't tested it, but it should be more or less correct.

public string ToSI(double d, string format = null)
{
    char[] incPrefixes = new[] { 'k', 'M', 'G', 'T', 'P', 'E', 'Z', 'Y' };
    char[] decPrefixes = new[] { 'm', '\u03bc', 'n', 'p', 'f', 'a', 'z', 'y' };

    int degree = (int)Math.Floor(Math.Log10(Math.Abs(d)) / 3);
    double scaled = d * Math.Pow(1000, -degree);

    char? prefix = null;
    switch (Math.Sign(degree))
    {
        case 1:  prefix = incPrefixes[degree - 1]; break;
        case -1: prefix = decPrefixes[-degree - 1]; break;
    }

    return scaled.ToString(format) + prefix;
}