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Lighting Circuit Connected Load Calculator

Calculate a lighting circuit's total connected load and check it against the standard 80% continuous-load derating limit.

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 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Total connected lighting load

720 W

High confidence
Circuit current draw
6 A
Maximum continuous load (80% of breaker)
16 A

With the figures above, the total connected lighting load comes to 720 W. 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 — 720 W — 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

  • Connected load = fixture count × watts per fixture; per NEC 210.19/210.20, a continuously-loaded branch circuit's total load must not exceed 80% of the breaker's rating (equivalently, the breaker must be rated at least load ÷ 0.8)

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Frequently asked questions

Why is the 80% continuous-load rule applied?
Per NEC 210.19/210.20, when a branch circuit supplies a continuous load (on for 3 hours or more, which most lighting circuits are), its total load must not exceed 80% of the breaker's rating — equivalently, the breaker must be rated at least the load divided by 0.8. This calculator checks the circuit's actual current draw against that 80% threshold.
How is the connected load calculated?
Connected load in watts is simply the number of fixtures multiplied by the watts per fixture. Dividing that by the circuit voltage gives the circuit's current draw in amps, which is then compared to 80% of the breaker rating.
What if my circuit fails the 80% check?
A failing result means the connected load draws more current than the continuous-load limit allows for the breaker size entered. Reduce the number of fixtures or wattage per fixture on that circuit, or move to a higher-rated breaker and conductor sized to match.