Sizing your Landscape Lighting Transformer:

 

Sizing: This is likely the most important calculation to make when choosing a transformer for your landscape lighting system, and luckily it a very simple calculation. To make the size calculation you simply add up the wattage of all the fixtures you intend to install and this is the total wattage of the system.  It's also recommend to multiply this number by 1.25, to ensure you have room to expand the system after the initial installation. 

Example: If you have 15 fixtures each with a wattage 4W and 8 fixtures with a wattage of 3W, your total wattage needs would be (4 x 15)+(8 x 3) x 1.25 = 105 Watts.  For this calculation you would likely choose a 150 W Transformer which would give you plenty of room for system expansion if needed.