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Outdoor String Light Calculator

Estimate the total string light length and bulb count needed for a patio or backyard space.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.1.0

Market
Imperial · sales tax
49.21 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

String light length needed

54.13 linear ft of string lights

Check your inputs

Sag allowance varies with how tightly the lights are strung — a straighter, more taut installation needs less allowance than a deliberately draped, scalloped look.

Bulb count
55 bulbs

For the dimensions entered, expect a string light length needed of 54.1 linear ft of string lights. Note that total run length sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • String lights drape with some sag between mounting points, adding roughly 10% beyond a straight-line perimeter measurement

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Frequently asked questions

Why do string lights need extra length beyond the straight-line distance?
Lights strung between two points naturally sag in the middle (a catenary curve), and a deliberately scalloped or draped look adds even more length — budgeting extra avoids running short right before the last connection point.
How many strings can I connect end-to-end?
Check your specific product's maximum connectable run — many LED string lights can be connected end-to-end for a much longer combined run than incandescent strings, which are often limited to just a few connected together before voltage drop dims the far end.
Do I need a transformer for outdoor string lights?
Most plug-in string lights run directly on standard household voltage and don't need a separate transformer — that's mainly a consideration for low-voltage landscape lighting systems (see the Landscape Lighting Transformer Calculator), a different product category.