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Landscape Lighting Wire Calculator

Calculate voltage drop for a 12V landscape lighting run, to check if your wire gauge is adequate for the run length.

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 2026-08-25 · v1.0.0

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

Voltage drop

0.8 V drop

Check your inputs

Voltage drop is moderate — acceptable for most installs, but a thicker wire would improve brightness consistency.

Current draw
5 A
Voltage drop
6.64 %
Voltage at fixture
11.2 V

With the figures above, the voltage drop comes to 0.80 V drop. The method behind this is well established, though site conditions and material batches will move it somewhat. This is calculated for United States and cites IRC 2024. Building in another market? Change the selector above so the units and code reference follow.

Add the equipment this sizes

This result is a specification — 0.797 V drop — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

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

  • Voltage drop (round trip) = 2 x current (A) x resistance per foot x length (ft), using standard copper wire DC resistance tables
  • For 12V landscape lighting, keeping voltage drop under about 10% (1.2V) is a common guideline to avoid dim or flickering fixtures

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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 is this safe to calculate without an electrician, unlike household wiring?
12V landscape lighting operates at a low enough voltage that the worst-case outcome of a sizing mistake is dim or flickering lights, not a shock or fire hazard — a fundamentally different risk profile than household 120V/240V circuits.
What if my voltage drop is too high?
Use a thicker wire gauge (lower AWG number), shorten the run, split the fixtures across two shorter runs from the transformer, or reduce the number of fixtures on that run.
Does this apply to 120V household extension cords?
No — this is specific to 12V landscape lighting wire and transformers. Household extension cord and circuit sizing involves different safety codes and higher stakes; consult an electrician for that.