[Radioroslyn]

Hi Ken,
Perhaps this will shed some light on this issue.

1.2 Resistor Dissipation

If the flow of current through a resistor increases,  it heats up, and if the temperature exceeds a certain critical value, it can be damaged. The wattage rating of a resistor is the power it can dissipate over a long period of time.
Wattage rating is not identified on small resistors. The following diagrams show the size and wattage rating:

[Image: http://www.mikroe.com/old/books/keu/01/1-3.gif]

Fig. 1.3: Resistor dimensions

Most commonly used resistors in electronic circuits have a wattage rating of 1/2W or 1/4W. There are smaller resistors  (1/8W and 1/16W) and higher (1W, 2W, 5W, etc).
In place of a single resistor with specified dissipation, another one with the same resistance and higher rating may be used, but its larger dimensions increase the space taken on a printed circuit board as well as the added cost.

Power (in watts) can be calculated according to one of the following formulae, where U is the symbol for Voltage across the resistor (and is in Volts), I is the symbol for Current in Amps and R is the resistance in ohms:

They don't show a 5w resistor but it is about the same length as the 2w but is a bit fatter about 9mm or3/8 "

GL
Terry