--data
declare @t table (postcode varchar(7))
insert @t
          select 'K1A 0B1'
union all select 'H0H 0H0'
union all select 'K0H 1T3'
union all select 'H4H 5T5'

--calculation
select postcode, dbo.NTODEC(replace(postcode, ' ', ''), 36) from @t

/*results
postcode             
-------- ----------- 
K1A 0B1  1211470093
H0H 0H0  1028718756
K0H 1T3  1210119015
H4H 5T5  1035444137
/*

--NTODEC function
GO
CREATE function NTODEC(@s VARCHAR(255), @b int) returns int as
BEGIN
    DECLARE @i int, @temp char(1), @result int
    SET @i = 1
    SET @result = 0
    WHILE (@i<=LEN(@s))
    BEGIN
        SET @temp = UPPER(SUBSTRING(@s, @i, 1))
        IF (@temp >= '0') AND (@temp <= '9') 
        	SELECT @result = @result + (ASCII(@temp)-48) * POWER(@b, LEN(@s)-@i)
        ELSE
        	SELECT @result = @result + (ASCII(@temp)-55) * POWER(@b, LEN(@s)-@i)
        SET @i = @i+1
    END
    return @result
END