Electronic Circuits and Projects Forum

For the most part it is a matter of size (diameter)

These are approximations, but fairly close estimations.

A resistor that has a diameter more or less the equivalent to the spray tube of an aerosol can is probably 1/8W.

Each successive doubling in size are 1/4, 1/2 and 1W.

Look up a similar physical size resistor and note its power rating. That will be the rating of your resistor.

Originally Posted by ronsimpson

The 1% resistors are usually one size bigger than 5% parts.

Good point.