Measure what you want to light. You get the sets of lights and the nets to buy for each part of the house, and how many outlets and circuits they need.
Lights to buy
3 sets of 25 C9 bulbs and 3 net lights (4′ × 6′)about 90 W on LED · one 15-amp circuit · 2 runs from an outlet
Quick answer: outline the roofline with one C9 or C7 bulb a foot (12″ apart) plus 10%, so 60 ft of roofline takes 3 sets of 25 C9s. Cover each bush with a 4′ × 6′ net (one does a shrub up to 3 ft tall and wide), wrap a trunk every 4″ with mini lights, and give an evergreen about 50 lights a foot.
How to use the outdoor Christmas lights calculator
- Measure the roofline along the gutters and up each peak you want lit, and pick the bulb: C9 (the big classic bulb), C7 (a size smaller) or mini lights.
- Add the trim: the windows, doors and porch railings you want to outline, in feet. A 3 × 5 ft window is 16 ft all the way round.
- Count the bushes and give their height and width, and say whether they stand against the house (lit from the front) or on their own. A hedge takes its length.
- Add the trees: trunks you will wrap (how high, and the tape measure round the trunk) and evergreens you will cover (their height).
- You get the sets of lights and the nets to buy for each part, the watts on LED and on incandescent, how many runs from an outlet and how many 15-amp circuits, with a sketch of the plan.
The rules behind the numbers
Rooflines and trim. The Christmas Light Emporium’s planner counts “total linear feet of fascia × 1 bulb per foot for C9 at 12″ socket spacing” and tells you to “add 10% slack for corners and overlaps”; for mini strings, “match linear feet to string length and add 10%”. Its C7 and C9 sets “commonly use 12-inch spacing”, so a set of 25 bulbs covers 25 ft. A string of 100 mini lights “on 4″ spacing runs about 33 feet”.
Bushes and hedges. A standard 4′ × 6′ net covers about 24 square feet. Christmas Lights Etc says it “covers most standard shrubs up to about 3 feet tall and 3 feet wide”; for a bigger bush, the Christmas Light Emporium multiplies “the bush’s height and the distance around the widest point” and divides by the net’s 24 sq ft, rounding up. A bush against the house is lit from the front, so only half the way round counts. A hedge is its face: a 20 ft hedge 3 ft tall is 60 sq ft, “round up to 3 nets”.
Trunks and evergreens. A trunk takes the distance round it once for every wrap: the Emporium’s example wraps “one wrap every 3–4 inches of height”, so a 6 ft trunk 4 ft round takes 18 wraps, 72 ft of lights. This calculator wraps every 4″ with the lights 4″ apart and adds 10% for the drape. For a whole tree in the front yard, Homes & Gardens’ lighting expert Joel Worthington (Mr. Electric) suggests “around fifty bulbs per foot” of height: 25 for a softer look, 100 for a bright one.
Power. Incandescent mini lights draw “around 40 watts per 100-light string” and incandescent C9s “7 watts per bulb”; an LED C9 is “under 1 watt” and a 5mm LED string or net about 5 W (the Emporium’s circuit guide). A 15-amp, 120-volt circuit carries 1,800 W, and electricians plan lights left on for hours at 80% of it, 1,440 W. Energy.gov: “Up to 25 strings of LEDs can be connected end-to-end without overloading a wall socket.” The CPSC: “Use no more than three standard-size sets of lights per single extension cord.” Your set’s tag gives its own limit; it comes first.
What each part of the house takes
| Part | Measure | Rule | Buy |
|---|---|---|---|
| Roofline, gutters, peaks | its length | one C9 or C7 a foot (12″ apart), + 10% | sets of 25 bulbs (25 ft) |
| Windows, doors, railings | the length you outline | mini lights by length, + 10% | strings of 100 (33 ft at 4″) |
| A round bush | how tall, how wide | one net up to 3 × 3 ft; bigger: tall × around ÷ 24 sq ft | 4′ × 6′ nets |
| A hedge | length × height | its face ÷ 24 sq ft, rounded up | 4′ × 6′ nets |
| A tree trunk | how high, how far round | a wrap every 4″, lights 4″ apart, + 10% | strings of 100 |
| An evergreen | its height | about 50 lights a foot | strings of 100 |
Watts per set
| Set | Lights | LED | Incandescent |
|---|---|---|---|
| C9, 25 bulbs | 25 | about 25 W | 175 W |
| C7, 25 bulbs | 25 | about 25 W | 125 W |
| Mini lights, 100 | 100 | about 5 W | 40 W |
| Net, 4′ × 6′ | 150 | about 5 W | 60 W |
Four worked examples
A ranch house. 68 ft of roofline in LED C9s, six 3 × 5 ft windows (96 ft), a 20 ft hedge 3 ft tall and a maple wrapped 8 ft up, 30″ round: 3 sets of 25 C9 bulbs, 7 strings of 100 mini lights (4 for the windows, 3 for the trunk) and 3 nets, about 125 W.
Four round bushes on their own, 4 ft tall and 4 ft wide. Each is about 50 sq ft (4 ft × 12.6 ft round), so it takes 3 nets: 12 nets in all.
120 ft of roofline in incandescent C9s. 6 sets (150 bulbs) draw 1,050 W: inside one circuit’s 1,440 W, but the CPSC’s three sets a cord makes it 2 runs. The same roofline in LED C9s is about 150 W.
Two 12 ft evergreens by the drive. At 50 lights a foot each takes 600 lights: 6 strings of 100, 12 strings for the pair.
Common mistakes
- Measuring the roofline and forgetting the run to the outlet. The 10% is for the corners, the overlaps and the cord’s way back.
- One net per bush, whatever its size. A net does a shrub up to about 3 × 3 ft; a 4 ft bush standing on its own needs three.
- Wrapping a trunk with the lights too far apart. The wraps go every 3–4″; wider and the trunk looks striped.
- Chaining incandescent sets end to end. No more than three sets on one cord (CPSC); LED sets go much further, but the tag sets the limit.
- Plugging a whole incandescent display into one circuit. Lights left on all evening are planned at 1,440 W on a 15-amp circuit, and the porch light shares it.
Lighting the tree inside too? The Christmas tree lights calculator gives its lights, ornaments and garland. Plan the porch and the front of the house in the free 2D planner.
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Outdoor Christmas lights questions
How many Christmas lights do I need for my house?
Add it up part by part: one C9 or C7 bulb a foot of roofline plus 10% (3 sets of 25 for 60 ft), a 4′ × 6′ net for each bush up to 3 ft, mini strings for the windows and railings by length, and about 50 lights a foot for an evergreen.
How many strands of Christmas lights can you connect?
What the tag says first. As a rule, up to 25 LED strings end to end (Energy.gov), and no more than three standard incandescent sets on one extension cord (CPSC).
How many Christmas lights can I plug into one outlet?
A 15-amp circuit is planned at 1,440 W for lights left on for hours, shared by everything else on it. That is about 36 strings of 100 incandescent minis, or hundreds of LED ones; with LEDs the string’s own end-to-end limit comes first.
How do you put Christmas lights on bushes?
With a net: hold it by the top corners, plug end toward the outlet, throw it over the bush and tuck the edges into the lower branches. A 4′ × 6′ net covers a shrub up to about 3 ft tall and wide.
How do you wrap a tree trunk with Christmas lights?
Start at the bottom near the outlet and spiral up, one wrap every 3–4″. Each wrap takes the distance round the trunk, so a trunk 2 ft round wrapped 6 ft up at 4″ takes 18 wraps, about 36 ft of lights.
C9 vs C7 Christmas lights: which for the roofline?
C9 is the bigger bulb and reads from the street, so it is the usual roofline bulb; C7 is a size smaller, for things seen up close: a porch, a railing, a tree. Both are commonly 12″ apart, one a foot, and they do not share a socket.
How many watts do LED Christmas lights use?
Little: an LED C9 is under 1 W a bulb and a 5mm LED string or net about 5 W, against 7 W a bulb for an incandescent C9 and about 40 W for 100 incandescent minis.