Consultant Rates

In my experience, market value, demographics determines the rate.
Review some rates in the area for reference.
Our area (SoCal) rates span 150 to 300 per hour.

It really depends on the job, local resource constraints etc. The 3 times rule doesn't always apply. If you are an independent working for yourself or a small company, it's more like the 1.5 to 2 times rule. If there is a shortage of talent in the market place like Oracle DBA's or MS SLQ 7, then the 3 times rule works, but it's a hard sell, at least in Minnesota (MPLS/ST. Paul).
Experience also will play a large role in being able to set the rate. If you have a seasoned DBA, who stays current, it's possible to get 4 times a salaried rate.
So the bottom line is:
3 times the salaried position works about 80% of the time. Always try to get as much as you can, but be aware of your potential customers thresholds. It's easier to negotiate down that it is up.
I hope that helps.

Although the 3X approach may work I use a more in depth approach so that I can determine what my 'real' marketability will be.

You need to determine your bottom dollar and then the acceptable industry range for your particular skill set. To do this add up your living expenses and that means everything - your car, insurance, medical, dental etc. You should know what salary will support your current lifestyle.

Then you need to determine how many days you will be on the bench. This means vacations, training, downtime, business development, holidays etc.

Now you are ready to compute your rate as follows:

subtract the number of 'bench' days from the total working days in the year. This will be the maximum number of 'billable' days you can work.

Figuring on an 8 hour day you can now compute your hourly rate to maintain your standard of living.

Of course, you modify this method as needs be (and if I left something out you get the point anyway) but you will be surprised what you need to charge by the hour to meet your expenses. Maybe that's why the big guys charge so much. Also, if you are doing project based work then this method will not be used.

Keep in mind that the rate you charge must be in line with the acceptable rates for your skill set. That is determined by knowing your market.

This is the method I've used and it's worked well for me. I got it from a book I was reading when I had the same question you did but I can't remember the book.

Good Luck,

- D