Roofline Light Calculator • Griswold Lights

Measure each straight run of your roofline, tell the planner which lights you’re using, and it works out how many sets, how many separate starting points (because every set has a limit on how many connect end to end), how many clips, how long an extension cord, and whether the whole thing is safe on one circuit.

1. Your roofline

One row per straight run: each gutter/eave, and each rake (the sloped edge up to a peak). Measure along the edge, in feet.

2. Your lights

Bulb style Color Light set

Lit length per set (ft) Watts per set Connect limit (sets end to end) Bulb spacing (in, optional)

3. Power and hanging

Outlet to where the lights start (ft) Circuit Other things on that circuit (W, optional) Clips

A planning estimate, not electrical advice. Check each set's own label for its wattage and connect limit, use outdoor-rated cords and GFCI-protected outlets, and ask an electrician if you're unsure about a circuit.

How the planner works

Sets: total roofline length divided by one set’s lit length, rounded up.
Starting points: sets divided by the set’s connect limit, rounded up. Each starting point needs its own plug.
Clips: one per bulb (from the bulb spacing) or one every 12 or 18 inches, your choice.
Extension cord: the distance to the outlet plus 10% slack, rounded up to 25, 50 or 100 ft.
Power: sets × watts per set, compared with 80% of the circuit: 1,440 W on a 15 A circuit, 1,920 W on 20 A, at 120 V.

Take the lit length, watts and connect limit from the box or the product listing; they vary a lot between sets. Verified sets will appear in the drop-down as we test them. Everything you type stays in your browser; the “link to this plan” puts it in the address so you can share it.