What size transformer do you need?

To determine the size of a transformer you need, consider the total wattage of the devices you intend to power, as well as any potential peak loads. Calculate the required wattage by adding up the wattage of all connected devices, then add a safety margin (typically 20-25%). It's also important to consider the voltage requirements and type of load (resistive or inductive) to ensure compatibility. Consulting the manufacturer's specifications or a professional can help ensure you select the correct transformer size.