Countertop: These appliances sit on your countertop next to your cutting board and toaster. They don’t require any installation other than being plugged into a nearby electrical outlet.
Over-the-range: Also known as OTR, built-in, or microwave hood, these units are installed above your range, freeing up countertop space and providing a vent that sucks in and filters out smoke and odors from cooking. They require professional installation, as they will be attached to the cabinets or the wall behind them and hooked up to electrical wiring.
The most common size is just under 30 inches wide and about 16 inches deep. Most have a left to right door opening, but some high-end models may have a door that opens downward as on a conventional oven. Either way, check to ensure that any adjacent cabinet-door fittings will not block the microwave or make it awkward to open. Keep in mind. OTRs are less convenient to access, especially for children or anyone wheelchair-bound. Also, be aware that while they do provide ventilation, they don’t exhaust as well as a hood that vents to the outside.
Microwaves are rated by the number of watts that they give out. Wattage can vary from 500 to 1500. For the most part, the larger the oven, the higher the wattage and the faster the oven will cook. However, other factors, like the size and shape of the cavity, can also affect cooking time. You should find 800-1200 watts sufficient.
Be sure to measure both your space and the microwave you are considering purchasing, including its height to make sure it can fit under a countertop.
Microwave oven capacity is given in cubic feet but that number. doesn’t give you a realistic estimate of usable space. Virtually all microwaves have turntables and it’s more important to measure the turntable. Its diameter will affect how big a dish the oven will be able to hold. If you have a favorite microwavable baking dish, either measure it from handle end to handle end or bring it to the store to determine if it will be able to rotate on the turntable. There are a few models that give you the option of deactivating the turntable. However, microwaves heat more evenly with the turntable rotating so we only recommend that you plan on using that feature occasionally to warm up food on a large platter or cook a lasagna.