Landscape Lighting Transformer Calculator
Free transformer sizing tool for low-voltage landscape lighting. Enter wire runs in feet, AWG and fixture wattage — we recommend a size at 80% capacity and estimate voltage drop across your system.
Wire Run #1
Fixture #1
How to choose a landscape lighting transformer
Low-voltage landscape lighting (usually 12 V) needs a transformer sized for the total fixture load and the length of each wire run. Undersizing causes dim fixtures and early failures; oversizing wastes money and can still fail if wire gauge or voltage drop is ignored.
How this calculator works
Add each home run from the transformer, choose AWG, then list fixtures (or enter real wattage). We total the load, apply the 80% capacity rule, and estimate voltage drop so you can see whether a thicker cable or a multi-tap transformer is a better fit.
Wire gauge and run length (United States)
Thicker cable (lower AWG) carries power farther with less drop. As a practical guide for LED systems:
| Gauge | Typical max run | Best for |
|---|---|---|
| 12 AWG | Up to ~150–200 ft | Long paths, higher load runs |
| 14 AWG | Up to ~100–150 ft | Most residential layouts |
| 16 AWG | Up to ~65–100 ft | Short path/area runs |
| 18 AWG | Short only | Very short, low-wattage spurs |
If voltage drop is high, shorten the run, increase gauge, split into multiple home runs, or use a multi-tap transformer.
Why multi-tap transformers matter
Multi-tap units (12 V / 13 V / 14 V / 15 V) let you compensate for drop on longer US properties so fixtures at the end of the run stay bright. Pair the right tap with correct AWG after you calculate load.
Frequently asked questions
Why size a transformer at 80% capacity?
Manufacturers and pro installers leave headroom for heat, inrush, and future fixtures. Running near 100% shortens transformer life and leaves no margin if you add path lights later.
Can I daisy-chain fixtures on one wire run?
Yes, but the farthest fixtures see the most voltage drop. Keep total load and length within the calculator limits, or split long daisy chains into separate home runs from the transformer.
What if the calculated voltage drop is high?
Move to a thicker gauge (for example 14 → 12 AWG), shorten the run, add another home run, or use a higher multi-tap voltage. Recalculate after each change.
Should I use fixture “marketing” watts or measured LED watts?
Use the actual LED wattage on the fixture or lamp data sheet. Defaults in this tool are typical landscape LEDs and are only a starting point.
Do I need one transformer per wire run?
Not always. Smaller transformers often support one or two runs; larger units can feed several home runs if total load stays under 80% capacity. The calculator groups runs when that is practical.
Where can I buy transformers in the United States?
Browse our low-voltage transformers, request a quote via the Quote Center, or start from Tools & Support.
