The formula, in one line
Every patio string light estimate comes down to the same calculation:
(Perimeter you're lighting) × (1 + drape allowance) = feet of lights needed
For a rectangular patio lit on all four sides, the perimeter is 2 × (length + width). A 16 × 12 ft patio gives you 2 × (16 + 12) = 56 feet of straight-line distance. Add a gentle café drape of 15% and you land at roughly 65 feet.
That 15% is the part almost everyone forgets, and it's why so many people end up one strand short. Lights hung with a visible curve between supports cover less horizontal distance than their actual length.
Patio string light size chart
These figures assume a gentle café drape (+15%) and lights running around the full perimeter. Find the row closest to your space:
| Patio size | Perimeter | All 4 sides | 2 opposite sides |
|---|---|---|---|
| Small balcony | 10 × 8 ft | ~42 ft | ~23 ft |
| Compact patio | 12 × 10 ft | ~51 ft | ~28 ft |
| Average patio or deck | 16 × 12 ft | ~65 ft | ~37 ft |
| Standard pergola | 20 × 12 ft | ~74 ft | ~46 ft |
| Large patio | 20 × 16 ft | ~83 ft | ~46 ft |
| Extra-large deck | 24 × 20 ft | ~101 ft | ~55 ft |
| Wedding / party tent | 32 × 20 ft | ~120 ft | ~74 ft |
Round up to the next whole strand. If you need 65 feet and your strands are 48 ft, you're buying two strands (96 ft) — not one and a half.
Three things that change the number most
1. How deep you let the lights sag
Drape is the single biggest variable, and it swings your total by a third:
- Taut / straight (no extra) — pulled tight along a wall, fence, or pergola beam. Use this when lights are attached directly to a surface.
- Gentle drape (+15%) — the classic café look, a soft curve between posts. This is what most people picture, and it's the safest default.
- Deep swag (+30%) — dramatic U-shaped dips. Gorgeous over a dining area, but budget noticeably more feet.
On a 20 × 12 patio, that's the difference between 64 feet (taut) and 83 feet (deep swag) — a whole extra strand.
2. Whether you're lighting all four sides
Most patios only need lights on the sides people actually sit under. If one edge is against the house wall, you're often lighting three sides, not four. On a 20 × 12 patio:
- All 4 sides — 64 ft of perimeter → ~74 ft with drape
- 3 sides (house wall excluded) — 52 ft → ~60 ft with drape
- 2 opposite sides — 40 ft → ~46 ft with drape
3. The distance to your outlet
This one catches people out constantly. Your calculated footage covers the lit area — it does not include the run from the first bulb back to the power source. If your outlet is 15 feet from the corner where your lights start, you need either a longer lead or an outdoor-rated extension cord to cover it.
Tents, canopies, and gazebos
The same perimeter formula works for anything rectangular, including an event tent. Take a common wedding tent that measures 32 feet long by 20 feet wide, with lights running around the entire edge with no breaks:
- Length around the edge (perimeter): 2 × (32 + 20) = 2 × 52 = 104 feet.
- Minimum length of lights needed: also 104 feet, since the lights must cover the whole perimeter. That's the figure if the strand runs pulled taut.
- With a gentle drape: 104 × 1.15 ≈ 120 feet. Most tent lighting is swagged between the poles, so this is the number to actually buy.
In strands, 120 feet is three 48-ft strands (144 ft) or two 100-ft strands. For a round or square canopy, use the same idea: a square is 4 × one side, and a round gazebo is about 3.14 × its diameter.
Zig-zag and crisscross patterns
If you're running lights across a patio rather than around its edge — the crisscross or zig-zag look — the perimeter formula doesn't apply. Instead, measure each individual run and add them together.
A common setup is three parallel runs across a 25 ft wide patio: 3 × 25 = 75 feet of straight-line distance, plus 15% drape = about 86 feet, plus the vertical drop at each end from the wall or post down to the attachment point (usually 2–4 ft per end).
The calculator's "Straight runs across yard" tab handles this pattern including the end drops.
How many strands is that?
Retail string light strands are most commonly sold in 24, 48, and 100 ft lengths. Here's how the common patio sizes translate:
| Feet needed | 24-ft strands | 48-ft strands | 100-ft strands |
|---|---|---|---|
| ~42 ft | 2 | 1 | 1 |
| ~65 ft | 3 | 2 | 1 |
| ~83 ft | 4 | 2 | 1 |
| ~101 ft | 5 | 3 | 2 |
Should you buy extra?
Yes — and not just a little. Buy to the next whole strand rather than cutting it close, for three practical reasons:
- Your first hang is rarely your final hang. Most people re-position at least once, and repositioning usually means more slack, not less.
- String lights are frequently discontinued. A matching replacement strand two seasons from now may not exist.
- Leftover length lets you extend the run to a nearby tree or fence post later without re-buying the whole set.
Frequently asked questions
How many feet of string lights for a 20×12 patio?
About 74 feet for all four sides with a gentle drape — that's two 48-ft strands. Lighting only the two long opposite sides drops it to around 46 feet, which one 48-ft strand covers.
How many string lights for a 12×12 patio?
A 12 × 12 patio has a 48 ft perimeter. With a gentle 15% drape that's about 56 feet — so two 24-ft strands won't quite do it, and you'd want either three 24-ft strands or a single 100-ft run.
How many feet of string lights for a 32 × 20 ft wedding tent?
The edge of a 32 × 20 ft tent is 2 × (32 + 20) = 104 feet, so the minimum is 104 feet of lights pulled taut. With a gentle drape between poles, plan on about 120 feet: three 48-ft strands or two 100-ft strands.
Do I measure the patio or the roofline above it?
Measure the path the lights will actually travel. If you're attaching to posts at the patio corners, measure the patio. If you're running from the house eaves out to a pergola, measure that path instead — it's often longer than the patio itself.
How high should patio string lights hang?
Aim for 8 to 10 feet above the ground at the lowest point of the sag. Below 7 feet and taller guests will hit them; above 12 feet the light feels distant and the café ambience is lost.
Can I cut string lights to length?
Almost never. Standard plug-in string lights are a single wired circuit — cutting them breaks the strand and creates an electrical hazard. Only specific low-voltage cuttable rope-light products are designed for it, and they say so explicitly on the packaging.