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Calcimator

Landscape Lighting Transformer Calculator

Size a low-voltage landscape lighting transformer and calculate voltage drop, maximum cable run, and recommended wire gauge.

Inputs

W
ft
AWG

Results

Transformer Size

150 W

≈ 15 LED bulbs

Voltage Drop

1.33 V

Total Wattage50 W
Max Run at 10% Drop90.6 ft
Recommended Gauge16 AWG
How to Use This Calculator
  1. List each fixture type and its wattage, then enter the total number of each fixture.
  2. Calculate the total wattage load across all landscape lights.
  3. Enter a 20% safety margin to avoid overloading the transformer.
  4. Review the recommended transformer VA rating and select the next standard size above your total.
  5. Keep total load below 80% of transformer capacity for reliable long-term performance.

What each input means

Number of Fixtures
Total number of landscape light fixtures on the circuit.
Watts per Fixture
Wattage of each fixture (LED typically 3-8W, halogen 20-50W).
Cable Run Length
Distance from transformer to the farthest fixture.
Cable Gauge (AWG)
Wire gauge: 10, 12, 14, or 16 AWG (lower = thicker = less voltage drop).

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Number of Fixtures = 10, Watts per Fixture = 5, Cable Run Length = 100, Cable Gauge (AWG) = 12 = 4 input(s) provided
  2. Calculate Transformer Size
    Transformer Size
    150 = 150
  3. Calculate Voltage Drop
    Voltage Drop
    1.33 = 1.33
  4. Calculate Total Wattage
    Total Wattage
    50 = 50
  5. Calculate Max Run at 10% Drop
    Max Run at 10% Drop
    90.6 = 90.6

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