A lot of microwave meals say on the packaging how long they need to heat up at a certain power, but what do you need to do if your microwave doesn't support that wattage?
This site helps you with microwave cooking time conversion, so you can easily convert the time a frozen dinner needs to defrost. Enter the time and the watt from the packaging and the power that your microwave supports. Your personal cooking time will be shown below the form.
There are no guarantees with this advice, but the experiences teach us that you'll have a tasty dish after the beep.