Outdoor Landscape Lighting Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 27, 2026Outdoor Landscape Lighting Calculator
Sizing a low-voltage landscape lighting transformer correctly means calculating total system wattage and building in a safety margin - undersizing leads to dim lights or transformer strain, while correctly sizing leaves room to grow.
Formula
Total Wattage = Number of Lights x Watts Per Light
Recommended Transformer Wattage = Total Wattage x 1.25 safety margin
Example
15 lights at 5 watts each:
Total Wattage = 75W → With Margin = 93.8W → Recommend a 100W transformer (next standard size up)
Why the 25% Safety Margin
A transformer sized right at the exact calculated load leaves no headroom for adding fixtures later, and running any transformer continuously at its absolute maximum rated capacity can shorten its operational lifespan - the 25% margin provides both future expansion room and more sustainable long-term operation.
Standard Transformer Sizes
Landscape lighting transformers come in standard wattage increments (commonly 45W, 60W, 100W, 150W, 200W, 300W, and 600W) - rounding your calculated need up to the next standard size is the practical way to translate this math into an actual equipment purchase.