Chris is correct, there are various calculators available out there.

However, the reason that I have done one myself was that I have found that most of the "off the web" calculators are imperial not metric, so I have to do two sets of calculations. Also, some of the things that I work in are a mixture of the two.

As such, the

power loss calculator that I did does Feet*

AWG, Meters*

AWG and Meters*mm. If anyone does want this, you can get it here:

http://www.mmp.au.com/downloads/plc.zip
Additionally, this one actually takes the simple calculation of working out resistance (as you need a reference chart) and combines it with another calculation to work out the

power loss in a specific length of a specific diameter cable. For this fact, I recommend that you read the following post for the background reference, especially the one by DMXtools, as this describes the math and reasoning behind this. In fact, DMXtools has done all the work, I simply took his information and put it into an Excel spreadsheet.

http://www.controlbooth.com/ftopic-1239-0.html
For the purpose of simply calculating the resistance of a length of cable, all you need to fill out is the length of the cable and the diameter of the conductors.

In fact, the only reason that I mentioned the calculator on this forum was because I had already given it to Zac when I initially done it.