The total of those wattage ratings will help you determine which gauge size you will need. Follow these additional safety tips when using extension cords with power tools and garden appliances. Look for the UL Mark on extension cords you purchase. The UL Mark means that representative samples of the cord have been tested for foreseeable safety hazards. Store all cords indoors when not in use.
Outdoor conditions can deteriorate a cord over time.
Never keep an extension cord plugged in when not in use. The cord will still conduct electricity until it is unplugged from the outlet. Most newer, indoor cords with more than one outlet have covers for the unused openings - use them. Children and pets face serious injury if they chew on unused outlets or stick sharp metal objects into the openings. Do not use extension cords that are cut or damaged.