Measure the space available. This means the width of the space, depth and the height in the area where the microwave will sit. Allow 1 or 2 inches of clearance on the back of the appliance to allow for ventilation when the unit is operating. If you have a casserole or other type of dish that you use frequently, measure it as well to ensure it fits in the appliance.
Write down the measurements and take them with you when shopping for the microwave.
Pick a microwave with the highest amount of wattage -- typically 1350 watts -- if speed is an important factor in your busy lifestyle or you have a large family. Most recipe directions are for a 600- to 700-watt microwave. Larger amounts of food require longer cooking time; therefore, if you cook big quantities at a time, a higher wattage on the microwave is necessary if speed is an important factor.