Microwave Wattage Converter

Check the label inside the door or on the back of the unit. If no label is visible, use the water test: microwave 1 cup (240 mL) of cold tap water on full power and time how long it takes to boil. About 2 minutes points to 1,200 W, 2.5 minutes to 1,000 W, 3 minutes to 800 W, and 4 minutes to 600 W. Most countertop microwaves sold today are 900 to 1,200 W.

Microwave cooking time is inversely proportional to wattage. A recipe developed in a 1,000W microwave takes 43% longer in a 700W microwave (1,000/700 = 1.43x). Most published microwave recipes assume 1,000W. Always adjust time when your microwave differs from the recipe's assumed wattage.

If your microwave is lower wattage than the recipe, you cannot match it by lowering power: your only option is to cook longer at full power. The opposite works though: if your microwave is more powerful than the recipe, cooking at a reduced power level (say 70%) for the original time delivers about the same total energy and is gentler for foods like fish, casseroles, or sauces that scorch or split at full power.