Measuring your CCFL correctly is the most critical aspect of finding the right replacement lamp. There are many ways in which one can be measured but only one method is the excepted industry standard. It is important that you use only this method to ensure that when referring to a lamps length or diameter we all have the same points of reference.
Lamps are measured from the end of the glass to the end of the glass, excluding the electrodes solder joints or wires. In most cases it may be necessary to expose the lamp entirely by sliding back the small silicone end cap that covers the end of the lamp in order to get a proper end of glass to end of glass measurement. For further reference, refer below:
With the silicone cap slid back you can see the lamp above measures 290mm from the end of glass to the end of glass.
Using a caliper you can accurately measure the diameter of your lamp.
Wiring a CCFL Backlight Example Video: