Unit measurement and conrvesion

ProductID    Name      Rate   Unit          Baseunit   conversion
1            Item A    100    carton         Pcs             20  
2            item B    120    carton         Doz             10
3            item C    100    Kilogram       Gram             2 

Unit_id      Unit_Name      Parent_ID   Conversion 
1            Pcs              -       1
2            Doz              1       12
3            gram             -       1
4            Kilogram         3       1000

public enum Units
    {
        //Mass
        //Hectogram = 0,
        Grams = 1,
        KiloGrams = 2,
        Pounds = 3,
        //Ounces = 4,
        //Tonnes = 5,
        //MilliGram = 6,

        //Length
        Metres = 101,
        Millimetres = 102,
        Centimeters = 103,
        Feet = 106,
        Inches = 107,
        
        //Volume
        Litres = 201,
        Millilitres = 202,
        FluidOunces = 204,
        
        //Quantity
        Numbers = 401,
        Dozen = 402,
        Carton = 400
    }

    class UnitConverter
    {
        public static double CtnCount = 0;

        const int MassRange = 0;
        const int LengthRange = 100;
        const int VolumeRange = 200;
        const int Quantity = 400;

        static double[] ToBaseWeight = new double[7];
        static double[] ToBaseLength = new double[8];
        static double[] ToBaseVolume = new double[10];
        static double[] ToBaseQty = new double[7];


        static UnitConverter()
        {
            //ToBaseWeight[(int)Units.MilliGram] = 1 / 100;
            ToBaseWeight[(int)Units.Grams] = 1;
            //ToBaseWeight[(int)Units.Hectogram] = 100;
            ToBaseWeight[(int)Units.KiloGrams] = 1000;
            //ToBaseWeight[(int)Units.Ounces] = 28.3495231; 
            ToBaseWeight[(int)Units.Pounds] = 453.59237;
            //ToBaseWeight[(int)Units.Tonnes] = 1000000;
            ToBaseLength[(int)Units.Metres - LengthRange] = 1;
            ToBaseLength[(int)Units.Millimetres - LengthRange] = 0.001;
            ToBaseLength[(int)Units.Centimeters - LengthRange] = 0.01;
            ToBaseLength[(int)Units.Feet - LengthRange] = 0.3048;
            ToBaseLength[(int)Units.Inches - LengthRange] = 0.0254;
            ToBaseVolume[(int)Units.Litres - VolumeRange] = 1000;
            ToBaseVolume[(int)Units.Millilitres - VolumeRange] = 1;
            ToBaseVolume[(int)Units.FluidOunces - VolumeRange] = 29.5735296;
            ToBaseQty[(int)Units.Numbers - Quantity] = 1;
            ToBaseQty[(int)Units.Dozen - Quantity] = 12;
            ToBaseQty[(int)Units.Carton - Quantity] = 100;
        }


        public static string ConvertUnits(double amount, Units from, Units to,double cnt)
        {
            CtnCount = cnt;
            if (from == to) return amount.ToString();

            string msg = ValidateUnitMatch(from, to);
            if (msg != "")
            {
                return msg;
            }

            int range = GetConversionRange(from);

            double[] rateArray = GetConversionArray(range);

            double answer = 0;
            //Convert From to base,
            if (CtnCount>0)
            {
                rateArray[0] = CtnCount;
            }
            
            answer = rateArray[(int)from - range] * amount;

            //Convert base to To
            answer = answer * (1.0 / rateArray[(int)to - range]);
            return answer.ToString();
        }

        static string ValidateUnitMatch(Units from, Units to)
        {

            int frange = ((((int)from) / 100) * 100);
            int trange = ((((int)to) / 100) * 100);

            if (frange != trange)
            {
                return "The from unit and to unit are not compatible. They need to be of the same type (Volume/Area/Mass/Length)";

            }
            else
            {
                return "";
            }
        }
        static int GetConversionRange(Units unit)
        {
            int range = ((((int)unit) / 100) * 100);
            return range;
        }

        static double[] GetConversionArray(int range)
        {
            switch (range)
            {
                case VolumeRange: return ToBaseVolume;
                case LengthRange: return ToBaseLength;
                case MassRange: return ToBaseWeight;
                case Quantity: return ToBaseQty;
            }
            throw new ArgumentOutOfRangeException("Unknown unit type");
        }
    }