How to size a C9 Christmas light install kit

Step 1 — Measure linear feet

Walk the roofline and measure every run you intend to light: primary rooflines, gable edges, secondary architectural lines (window frames, columns, entry arches), and any auxiliary runs (fascia returns, deck railings, garden borders). A 100-foot tape works for smaller residential jobs; a wheel measure is faster on commercial jobs.

Include the vertical drops at gables and hip returns — installers commonly under-measure vertical runs because they don't read as continuous roofline from the ground. Include any planned secondary lighting even if the primary contract is roofline-only, because a homeowner add-on request on install day is common and having spare spool footage saves a re-trip.

For estimation on a job you can't walk, satellite imagery on Google Maps at maximum zoom gives usable linear footage on rectangular residential rooflines. Multiply by 1.15 to account for gable pitches that satellite view flattens.

Step 2 — Pick bulb spacing

Bulb spacing determines the look and the parts count. Standard installs use 12-inch spacing, which reads as a continuous line of light from the ground and gives a balanced look on most residential and commercial architecture. 15-inch spacing gives a slightly wider look with fewer parts (and a slightly lower total cost). 6-inch and 9-inch spacings are used for dense luxury installs and high-visibility commercial work where the runs need to read as a solid ribbon of light rather than distinct bulb points.

24-inch, 36-inch, and 48-inch spacings are used on long-run applications like driveway edge lighting, market lights, and low-density commercial perimeter runs where distinct bulb-point lighting is the design brief.

Step 3 — Pick the wire gauge

Residential installs use SPT-1 (18 AWG standard insulation). Commercial installs use SPT-2 (18 AWG heavier insulation) — many commercial jurisdictions require SPT-2 by electrical code. Confirm with the property's electrical inspection authority before speccing on a commercial job.

Step 4 — Calculate spool count, bulb count, and clip count

Total bulbs = (linear feet × 12) / bulb spacing inches. Add 8 percent overage to cover install-and-take-down breakage. Round up to the nearest 25-count pack.

Spool count = round-up-to-stock-length. Christmas Light Supplier stocks spools in 250-ft, 500-ft, 1,000-ft, 2,000-ft, and 4,000-ft lengths. For a job under 250 feet, one 250-ft spool. For a 1,000-ft job, one 1,000-ft spool. For a 1,200-ft job, one 1,000-ft plus one 250-ft spool (some slack on the 250-ft — normal).

Clip count = same as bulb count plus 8 percent overage, rounded to 25-count packs.

Plugs = one male-plus-female pair per spool (line-in and end-of-run). Photocell timer = one per install line.

The Kit Builder tool at /kit-builder runs this exact math live for any feet + spacing + wire + clip combination.

Rules of thumb from job experience

On a first-year contract, order 15 percent extra bulbs and clips rather than 8 percent — first-year installs tend to have more breakage as the crew learns the property. Reduce overage in subsequent years once the crew is dialed in.

On a job with a homeowner or property manager who may request add-ons mid-install (deck lights, tree wraps, wreath backlighting), pack one extra 250-ft spool and one extra 25-count bulb pack in the van as opt-in inventory. The margin on same-visit add-ons is high and the extra parts are cheap insurance against needing to leave the job for supplies.