How to use this string light calculator
Pick the tab that matches your project, type in a few measurements, and the results update as you type. Here's what each mode is for:
- Patio / Deck perimeter — for lights that run around the edge of a rectangular patio, deck, pergola, gazebo, or event tent (a 32 × 20 ft tent is 104 ft around the edge). Enter the length and width and choose how many sides you're lighting.
- Straight runs across yard — for lights strung in parallel lines between posts, a house and a fence, or across a backyard. Enter how many runs and how long each one is.
- Wrap a tree — for spiraling lights up a trunk (and optionally out onto branches). Enter the height you'll cover and the trunk circumference.
- Roofline / house — for outlining your roof edges, eaves, and gables with lights (great for Christmas displays). Enter the length of roofline you're covering and how many peaks it has.
How many string lights do I need? (quick reference)
If you just want a fast estimate before measuring, these are typical amounts. Your exact number depends on hang style, which the calculator handles for you.
| Space | Typical size | Feet of lights (gentle drape) |
|---|---|---|
| Small balcony / patio | 10 × 8 ft | ~40 ft |
| Average patio or deck | 16 × 12 ft | ~65 ft |
| Large patio / pergola | 20 × 16 ft | ~80 ft |
| Backyard (3 straight runs) | 3 × 25 ft | ~85 ft |
| Wrap one tree trunk | 8 ft high, 30 in around | ~60 ft |
| Outline a house roofline | ~120 ft of eaves + peaks | ~140 ft |
For a full breakdown by patio size — including three-sided layouts and crisscross patterns — see how many feet of string lights you need for a patio.
Hang styles: taut vs. draped vs. swag
The single biggest factor people forget is sag. Lights strung with a droop use noticeably more length than the straight-line distance:
- Taut / straight — pulled tight along a wall or edge. No extra length.
- Gentle drape (+15%) — the classic café look with a light curve between supports. The best all-round choice.
- Deep swag (+30%) — dramatic U-shaped dips. Beautiful, but budget noticeably more feet.
Can you connect several strands together?
Usually, but only up to the maximum printed on the box, and LED sets allow far more than incandescent ones. See how many strands you can safely connect for the limits by bulb type and how to work out yours.
Christmas lights
For a house, use the Roofline / house tab above. For a chart by house size and tips on measuring from the ground, see how many Christmas lights you need for a roofline. Decorating indoors? See how many lights you need for a Christmas tree, by tree height.
Frequently asked questions
How many string lights to wrap a tree?
It depends on trunk thickness and how tightly you wrap. Wrapping the first 8 feet of a trunk that's 30 inches around, with medium 4-inch spacing, takes about 60 feet of lights. Thicker trunks and tighter spacing use more — the "Wrap a tree" tab calculates it from your measurements. See the full tree wrapping chart by trunk size.
Should I add extra length just in case?
Yes. Buy the next strand up rather than cutting it close — you'll want slack to reach the outlet, to re-position after your first attempt, and to replace any dead section later. The calculator already rounds up to whole strands and shows your leftover feet.
What size string lights should I buy — bulb spacing?
Bulb spacing (the gap between bulbs) changes the look, not the length you need. Wider spacing (12–18 in) gives an airy café feel; tighter spacing (6 in) looks fuller and brighter. Set your spacing in the calculator to see the approximate bulb count.
Can I use indoor string lights outside?
No. Use lights rated for outdoor or wet/damp locations, plug into a GFCI-protected outlet, and use outdoor-rated extension cords. Indoor-only sets can fail or become a hazard when exposed to rain and humidity.
String light guides
- How many feet of string lights do I need for a patio? — size chart from balconies to large decks
- How many string lights to wrap a tree? — footage by trunk circumference and spacing
- How many Christmas lights for a roofline? — chart by house size, and measuring from the ground
- How many lights for a Christmas tree? — lights and strands by tree height
- How many strands can you safely connect? — LED vs incandescent limits, and how to calculate yours
- Choosing the right outdoor string lights — length, bulb type, spacing, and weather ratings