Low-voltage planning
Transformer Size & Voltage Drop Calculator
Size a 12V landscape lighting transformer and check voltage drop for your wire gauge, run length and wiring method — with the tap setting to use.
Transformer & Voltage Drop
12V low-voltage systems · copper landscape cable
Fixtures on this run
Recommended transformer
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- Total LED load
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- Current on the run
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- Voltage drop
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- Suggested tap
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- Voltage at fixtures
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How the Calculator Works
Low-voltage landscape lighting steps 120V house power down to about 12V. Two numbers decide whether a system performs: transformer load and voltage drop.
- Transformer size: add up fixture wattage and divide by 0.8. Running a transformer at 80% or less keeps it cool and leaves room to add fixtures.
- Voltage drop: current flowing through cable loses voltage over distance. We use V = 2 × L × I × R ÷ 1,000, where L is run length in feet, I is amps (watts ÷ 12) and R is the cable resistance per 1,000 feet.
- Taps: multi-tap transformers offer 12, 13, 14 and 15V outputs, so you can push a little extra voltage down a long run and land near 11–12V at the fixtures.
| Wire gauge | Resistance (Ω per 1,000 ft) | Typical use |
|---|---|---|
| 16 AWG | 4.02 | Fixture leads, very short runs |
| 14 AWG | 2.53 | Light loads under ~60W, short runs |
| 12 AWG | 1.59 | The workhorse for most home runs |
| 10 AWG | 1.00 | Long runs and heavy loads |
| 8 AWG | 0.63 | Feeder runs to distant hubs |
Why Hub Wiring Matters
Daisy-chaining fixtures along one cable puts the full load at the far end, so the last lights are dimmer. Hub (or split-load) wiring runs a heavier cable to a central point and branches out with short, equal leads — every fixture sees nearly the same voltage. It is standard practice on Landscape Lighting Texas installations. Learn more in our low-voltage lighting guide.
FAQ
Frequently Asked Questions
What size transformer do I need?
Total your LED wattage and divide by 0.8, then round up to the next standard size (75W, 150W, 200W, 300W and so on). Leave room for future fixtures.
How much voltage drop is acceptable?
Aim for fixtures between about 10.8V and 12V. Most LEDs tolerate a wider range, but consistent voltage keeps brightness and color even.
Do I need an electrician?
Low-voltage cable work generally does not, but adding a new 120V outlet or circuit for the transformer should be done by a licensed electrician.
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