Hi

The smaller the watt rating, the higher the likelihood that overheating during soldering can damage it.

The watt rating is unfortunately, to eyeball them. Match 2 different sized resistors you actually have to this image but scale it to life size, then you have an estimated watt scale.

From left to right, the wattage ratings are:7 watt, 10 watt, 2 watt, 1 watt, 1/2 watt, 1/4 watt and a 1/8 watt.

Neilm is right, in circuit measurement of a resistor is likely to be off, some older DMM have a low volt ohms capacity but the most reliable way unfortunately is to desolder it.