Count Lights by Their Input Amps, Not Their Brightness

A standard 15-amp, 120-volt circuit can support 24 incandescent 60-watt bulbs running continuously, provided nothing else uses the circuit and the wiring and controls are suitable. There is no universal fixture count: the standard continuous-load allowance is 12 amps, so LED units rated at 0.10 amp each have a calculated limit of 120 on an otherwise unloaded circuit. Those are load calculations, not permission to install that many lights.

A continuous load is one expected to remain at maximum current for three hours or more. The standard sizing rule requires the breaker rating to cover 125% of continuous load plus 100% of noncontinuous load. For an entirely continuous load, 15 ÷ 1.25 = 12A. Eaton’s January 2026 application paper explains both the requirement and the three-hour definition.

Enter each light’s rated input amps and the loads sharing the breaker; the calculator treats the proposed lights as continuous.

The calculator uses a fixed 15A breaker rating. Its result is an arithmetic ceiling for identical lights, not a check of your wiring, dimmer, installation or local code. Use a light’s input-current rating specified for 120V. If that rating is missing, the calculator cannot establish it from an advertised watt-equivalent value.

A 12-Amp Allowance Gives These Calculated Light Counts

These examples assume an otherwise unloaded 120V circuit, all lights operating continuously, and suitable wiring and controls. The LED entries are examples of labeled input ratings—not claims about every LED bulb with a particular brightness.

Light Or Fixture Rating	Current At 120V	Count Within 12A
60W incandescent bulb	0.50A	24
100W incandescent bulb	About 0.83A	14
LED unit labeled 0.10A input	0.10A	120
LED unit labeled 0.20A input	0.20A	60
LED unit labeled 0.50A input	0.50A	24

For identical lights, light count equals available continuous-load amps divided by input amps per light, rounded down.

Rounding down matters because a partial fixture is not usable capacity. For the 100W incandescent example, calculate with 100 ÷ 120 rather than treating the displayed, rounded 0.83A as an exact rating. The resulting whole-light count is 14.

The unit you count must match the rating you use. If a fixture takes several separately rated bulbs, count every bulb. If you have the complete fixture’s input-current rating, count the fixture as one unit and use that rating. Do not use a whole-fixture rating and then multiply it by the number of bulbs inside the fixture; that would count the same load twice.

Likewise, do not assume that every recessed light, pendant or plug-in lamp draws the same current because it looks similar. The table only supports the stated ratings. A mixed collection of lights needs a total of their individual input currents rather than one count based on the smallest lamp.

Continuous Operation Changes The Breaker-Sizing Calculation

The 12A allowance comes from the continuous-load sizing rule, not from a claim that a 15A breaker becomes a 12A breaker. A load expected to stay at maximum current for three hours or more receives the continuous-load treatment. That can apply to lights left on throughout an evening or used for sustained work, depending on their expected operation.

For mixed loads, the standard breaker-sizing check is: 1.25 × continuous amps + noncontinuous amps ≤ 15A.

The distinction matters when lighting shares a circuit with equipment that does not operate continuously. Do not put every load into the continuous category simply because it is connected to the circuit. Conversely, do not classify a sustained lighting load as noncontinuous just to make the count larger. The categories should reflect the expected operation of the loads you are evaluating.

The calculator treats the proposed lights as continuous throughout. That makes its answer consistent with the 12A examples, while allowing you to enter other continuous loads and, optionally, noncontinuous loads separately. It is not a tool for determining whether a particular appliance qualifies as continuous.

The 80% rule is not a blanket limit for every short-duration load, and it does not mean the breaker trips precisely at 12A. Eaton explains the distinction between continuous and noncontinuous loading. A breaker that has not tripped is therefore not evidence that a proposed continuous lighting load meets the sizing rule.

LED Input Amps Matter More Than Watt Equivalents

At 120V, 15A corresponds to 1,800 volt-amperes (VA). The 12A continuous-load allowance corresponds to 1,440VA. For incandescent bulbs, whose power factor is approximately 1, that is also about 1,440 watts.

This is why dividing 1,440 by the wattage of an incandescent bulb gives a useful load-count example. It is not a universal method for counting LED fixtures. LED drivers can have a lower power factor, so dividing 1,440 by LED watts can overstate the number the circuit supports.

Use the luminaire’s rated input amps when available. Mike Holt’s load-calculation guidance, based on the 2020 NEC, specifies ampere ratings for LED-driver lighting loads rather than lamp wattage. Match that rating to the supply voltage: a current value specified for another voltage does not establish the unit’s current at 120V.

Also separate actual electrical consumption from brightness equivalence. A “60W-equivalent” LED is not necessarily a 60W electrical load. The Department of Energy’s lighting guide explains that watts measure electrical power while lumens measure brightness.

The words “60W equivalent” alone are therefore insufficient for this calculation. They do not tell you the LED’s input amps, and they should not be entered as actual watts. Look for the electrical input information on the product label or in the manufacturer’s specifications for that exact model.

If the information you have gives only actual LED watts and no input-current rating, the precise count remains unknown from that information alone. This article does not supply a generic LED power factor to fill the gap. Substituting an assumed value would make the result look more certain than the available product data supports.

Shared Loads Reduce The Number Of Lights You Can Add

Include existing lights, plug-in lamps, fans and appliances supplied by the same circuit—not just the room where you want another light. The relevant boundary is the circuit served by the breaker, not the room name or the wall switch controlling the proposed fixture.

For example, if other continuous loads total 3A, the remaining continuous allowance is 9A. Lights rated at 0.10A each would then have an arithmetic limit of 90, before control and installation limits. Using the unloaded-circuit count of 120 would ignore the current already committed to those other loads.

Keep the proposed lights separate from the shared-load entry. If you are calculating how many new lights can be added, enter existing continuous lighting under other continuous loads. If you are calculating the capacity for a complete group of identical lights, do not also enter that same group as an existing load.

Noncontinuous loads belong in their own part of the calculation. With proposed lights treated as continuous, available lighting amps equal (15 minus other noncontinuous amps) divided by 1.25, minus other continuous amps. Divide that remainder by the input amps of each proposed light and round down.

That formula is not the same as subtracting every load from 12A. The 125% multiplier applies to continuous loads, while noncontinuous loads enter the standard sizing check at 100%. Keeping the categories separate preserves that distinction.

An unknown shared load is not zero. If you do not know what else the breaker supplies, the unloaded-circuit result is only a hypothetical ceiling. Before adding permanent lighting, have an electrician verify the circuit capacity and locally adopted code requirements. The count calculation does not establish those conditions by itself.

A Dimmer Or Switch Can Set A Lower LED Limit

Even when the circuit-current calculation allows more lights, the control may not. Follow the dimmer or switch manufacturer’s LED load and lamp-count limits, not just its incandescent wattage rating. Those limits apply to the specific control and compatible lighting arrangement; a breaker calculation cannot replace them.

Lutron’s application note on LED load limits explains these control limitations and the current spikes associated with LED loads. LED current spikes can also cause nuisance breaker trips. A low steady input-current total does not, by itself, establish that every proposed group of drivers will operate properly on the selected controls.

This is a separate check from the continuous-load arithmetic. The calculator answers how many identical lights fit within the stated breaker-sizing allowance. It does not know your dimmer model, its LED rating, the lamp compatibility requirements or any manufacturer-specified lamp-count limit.

A control’s incandescent wattage rating should not be treated as an interchangeable LED rating. Nor should the table’s count of 120 units rated at 0.10A be read as a recommendation to connect that many units to one dimmer. The usable installation must satisfy the applicable circuit and control limits, not merely the largest number produced by one calculation.

Repeated Trips Need Investigation, Not A Larger Breaker

Do not replace a 15A breaker with a larger one to fit more lights. Breakers protect circuit conductors, and their sizing must match the wiring. Changing the breaker rating is not a way to make the existing lighting calculation acceptable.

Repeated trips need investigation, even if your estimated steady lighting current appears to fit. The estimate may omit shared loads, use an incorrect product rating or overlook a control or current-spike issue. The arithmetic alone cannot identify the cause of a trip. ESFI recommends a qualified electrician for frequent breaker trips.

While the circuit is off, use independent power-failure lights, flashlights or lanterns rather than relying on that circuit for safe movement. That gives you usable light without depending on the circuit being investigated.

For a proposed installation, the useful number to bring to an electrician is the calculated load along with the exact fixture ratings, the other loads sharing the breaker and the intended controls. A count such as 24 incandescent bulbs or 120 low-current LED units describes one set of assumptions. Your actual allowable installation depends on whether those assumptions match the equipment and circuit.