Outdoor Lighting Calculator
Plan low voltage landscape lighting. Enter your path length and fixtures, and get the transformer size, total watts, total lumens and the wire gauge for your cable run.
| Detail | Result |
|---|---|
| Total lumens | 1,400 lm |
| Current at 12 volts | 3.2 A |
| Wire gauge | 14 AWG |
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How Outdoor Lighting Calculator Works
Four quick steps happen behind the screen every time you change a number.
Counts the path lights
Path length is divided by the spacing and one more light is added for the end of the path.
Adds up the load
Watts of path lights and spot lights are added together to give the total load.
Leaves headroom
The load is raised by 25 percent, then the next standard transformer size is chosen.
Checks the cable
Current and run length are used to pick a wire gauge that keeps the voltage drop small.
How to Use Outdoor Lighting Calculator
Five quick steps take you from a tape measure to a usable result.
- Measure the pathWalk the route you want to light and note the length.
- Choose the spacingSix to eight feet gives pools of light that overlap softly.
- Enter the fixture wattsRead the watts and lumens from the box of each light.
- Add your spot lightsSpots light up trees, walls and entries. Enter the count and the watts for each.
- Enter the longest cable runMeasure from the transformer to the farthest light and read the wire gauge.
Formula Used in Outdoor Lighting Calculator
These are the standard formulas behind every result, so you can check the numbers yourself.
Total load
All values are in watts.
Transformer
A 25 percent margin keeps the transformer cool.
Current
Low voltage systems usually run at 12 volts.
Worked example
A 60 ft path with lights every 8 ft needs 8 lights at 3 W, which is 24 W. Two 7 W spots add 14 W for a total of 38 W. With the 25 percent margin that is 47.5 W, so a 60 W transformer fits, and 14 gauge wire suits a 50 ft run.
Transformer Size Chart
Standard low voltage transformer sizes and the working load they handle with a 25 percent margin.
| Transformer | Safe working load | Current at 12 V |
|---|---|---|
| 60 W | 48 W | 4.0 A |
| 100 W | 80 W | 6.7 A |
| 150 W | 120 W | 10.0 A |
| 200 W | 160 W | 13.3 A |
| 300 W | 240 W | 20.0 A |
| 600 W | 480 W | 40.0 A |
Keep your total fixture watts at or below the safe working load.
Lighting Load by Path Length
Path lights, watts and transformer for 3 W lights every 8 ft, with two 7 W spot lights.
| Size | Path lights | Total watts | Transformer |
|---|---|---|---|
| 20 ft path | 3 | 23 | 60 |
| 40 ft path | 6 | 32 | 60 |
| 60 ft path | 8 | 38 | 60 |
| 80 ft path | 11 | 47 | 60 |
| 100 ft path | 13 | 53 | 100 |
| 150 ft path | 19 | 71 | 100 |
Wire gauge depends on the cable run, so use the calculator for your own run.
Common Outdoor Lighting Mistakes
Four slips that throw off the result, and how to avoid them.
Choosing a transformer with no margin
A transformer run at its limit overheats. Choose a size at least 25 percent above the load.
Using thin wire on a long run
Voltage drops along thin cable, and lights at the end look dim. Use a thicker gauge for long runs.
Ignoring lumens
Watts show power, not brightness. Check lumens to make sure the light is bright enough for steps and paths.
Mixing light types without planning
Warm and cool light side by side looks uneven. Pick one colour temperature for the whole yard.
Tools You Must Know
One number is rarely enough for a yard project. These calculators pair well with this one.
Outdoor Lighting Calculator FAQs
Quick answers before you order materials.
How do I size a transformer for landscape lighting?
Add up the watts of every fixture, multiply by 1.25 and pick the next standard transformer size.
How many path lights do I need?
Divide the path length by the spacing and add one. Six to eight feet apart is typical.
What wire gauge should I use for outdoor lighting?
Short runs under 50 feet often use 14 gauge. Longer runs and higher loads need 12 or 10 gauge.
How many lumens does a path light need?
Path lights of 100 to 200 lumens are enough for safe walking. Spot lights need more.
Why do my last lights look dim?
Voltage drops along the cable. A thicker gauge or a second run from the transformer fixes this.
Is the Outdoor Lighting Calculator free?
Yes. It is free to use, with no signup.
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