Outdoor string lights turn a patio, deck or backyard into a place to linger in the evening. Planning the layout before buying avoids coming up a few feet short. This calculator handles the two most common layouts.
Perimeter or zigzag
- Around the edge: lights follow the perimeter of the patio, along a fence, a pergola or poles at the corners. Length = 2 × (length + width).
- Zigzag across: lights cross the space diagonally between anchor points on two opposite sides, making a canopy. Each run goes across the width and along one anchor spacing:
run length = √(width² + spacing²), total = number of runs × run length
For a 20 × 15 ft patio with anchors every 5 ft: 4 runs × √(15² + 5²) = 4 × 15.8 = 63.2 ft.
Allow for sag
Lights look best with a gentle drape, and you need slack to reach the anchors. Adding about 10% gives 69.6 ft. With 48 ft strands, you need 2 strands, carrying 48 bulbs at 2 ft spacing.
Power and connection
Most plug-in string lights can be connected end to end, up to a maximum number of strands stated on the package. LED strands of 1 W bulbs allow many more strands than incandescent bulbs of 7 to 11 W. Never exceed the manufacturer’s limit, use outdoor-rated extension cords and plug into a GFCI-protected outdoor outlet. A plug-in timer or smart plug turns the lights on at dusk.
Hanging them securely
- Use sturdy anchors: eye screws in fascia boards, fences or pergola posts, or dedicated light poles set in planters or footings.
- For long spans over about 20 ft, run a steel guide wire and clip the lights to it, so the wind does not stress the wire.
- Keep at least 7 to 8 ft of clearance overhead, more over walkways.
- The calculator counts anchors as one every spacing along the perimeter, or one per zigzag turn.
Choosing lights
Commercial-grade strands with shatterproof LED bulbs survive weather and last much longer than light-duty party strings. Warm white (about 2,200 to 2,700 K) gives the classic café look; a dimmer lets you set the mood.