Under Cabinet Lighting Calculator: LED Tape, Watts & Driver

Measure each stretch of wall cabinets that has counter under it. You get the LED tape for each one cut to its marks, the watts, the driver, the wire from the driver, and the lumens, from two makers' own data sheets. Or puck lights instead.

Your cabinet runs

in in

One box per stretch, inside the cabinets' side panels. A range hood, a window or the fridge ends a run: the next one starts past it. Round a corner? Two runs. Leave the rest blank.

The light

How bright

Volts

Wired

Driver to the lights ft

Wire gauge

The driver plugs in or is wired in a cabinet, often over the fridge or under the sink; the feed is the low-voltage wire from it to the first light.

Your under-cabinet lights

13′ 6″ of LED tape for your 4 runs1 leg · 28 W · a 36 W driver · 3,483 lumens

Your runs from the front.

From each maker

Draw your kitchen in the free 2D planner →

Quick answer: measure each run of wall cabinets inside its side panels, cut the tape only at its marks, and add the pieces up. On Armacost’s own chart, 13½–16 ft of its 12 V, 60 LEDs/m tape uses 28 W, so a 36 W driver. That tape runs 16.4 ft from one end; its 24 V twin runs 32.8 ft.

How to use the under-cabinet lighting planner

Measure each run of wall cabinets that has counter under it, inside the cabinets’ side panels. A range hood, a window or the fridge ends a run; the next one starts past it. A corner is two runs.
Pick the light: LED tape (a continuous line of light) or puck lights (round spots). For tape, pick how bright: soft glow, everyday or bright task, Armacost’s own three densities.

Pick 12 or 24 V and how the runs are wired: one run to the next with a short wire across each gap, or each run back to the driver on its own wire.
Enter the feed: how far the driver is from the first light, and the wire’s gauge. You get the tape for each run, the legs, the watts, the driver and the feed’s voltage drop, from Armacost and from Diode LED. Copy link to these lights keeps it all.

The tapes, side by side

Every figure is the maker’s own data sheet. A leg is tape fed from one end; past its longest run the far end dims.

Tape	Volts	Lumens a foot	Watts	Cut every	Longest run from one end
Armacost RibbonFlex Pro, 30 LEDs/m	12 V	129	4.5 W a metre	4″	32.8 ft (10 m)
Armacost RibbonFlex Pro, 60 LEDs/m	12 V	258	9 W a metre	2″	16.4 ft (5 m)
Armacost RibbonFlex Pro, 120 LEDs/m	12 V	427	15 W a metre	1″	16.4 ft (5 m)
Armacost RibbonFlex Pro, 30 LEDs/m	24 V	115	4.5 W a metre	6½″	65.6 ft (20 m)
Armacost RibbonFlex Pro, 60 LEDs/m	24 V	239	9 W a metre	4″	32.8 ft (10 m)
Armacost RibbonFlex Pro, 120 LEDs/m	24 V	402	15 W a metre	2″	32.8 ft (10 m)
Diode LED BLAZE, 100 lumen range	12 V	121	1.46 W a foot	2″	27 ft
Diode LED BLAZE, 200 lumen range	12 V	221	2.93 W a foot	1″	20 ft
Diode LED BLAZE, 100 lumen range	24 V	117	1.46 W a foot	4″	55 ft
Diode LED BLAZE, 200 lumen range	24 V	237	2.93 W a foot	2″	40 ft
Diode LED BLAZE, 300 lumen range	24 V	344	4.5 W a foot	2″	22 ft

Diode LED’s lumens are at 3000K. How bright, in Armacost’s words: 120 LEDs/m is “designed for task lighting”, 60 LEDs/m “bright enough for a broad range of undercabinet and accent lighting”, 30 LEDs/m “best for accent lighting applications”.

Watts and the driver, by length of tape

Armacost’s watts-used chart for one leg, read as it asks (“use the next longer length on the chart”), and the smallest of its standard drivers (12, 24, 36, 60 and 120 W) that carries it. A long leg uses fewer watts a metre than a short one.

Tape	12 V, 30 LEDs/m	12 V, 60 LEDs/m	12 V, 120 LEDs/m	24 V, 60 LEDs/m	24 V, 120 LEDs/m
4 ft	8.5 W → 12 W	16 W → 24 W	27 W → 36 W	16.9 W → 24 W	28.1 W → 36 W
8 ft	12 W → 12 W	22 W → 24 W	36 W → 36 W	24.6 W → 36 W	40.1 W → 60 W
12 ft	15 W → 24 W	25 W → 36 W	43 W → 60 W	31.2 W → 36 W	52.6 W → 60 W
16 ft	17.3 W → 24 W	28 W → 36 W	48 W → 60 W	37.5 W → 60 W	63.1 W → 120 W
20 ft	20.5 W → 24 W	2 legs, 50 W → 60 W	2 legs, 86 W → 120 W	47.1 W → 60 W	80 W → 120 W

Diode LED sizes its tape by its watts a foot: 13½ ft of the 200 lumen BLAZE is 39.6 W, and its dimmable driver “should be loaded to 80% maximum”, so it takes the 60 W one (48 W on it).

How long the feed wire can be, at 12 V

The low-voltage wire from the driver to the first light, before the drop passes Armacost’s 0.75 V or Diode LED’s 3% (0.36 V). Double these at 24 V.

Load	18 AWG	16 AWG	14 AWG
12 W	58 ft · 28 ft	93 ft · 44 ft	148 ft · 71 ft
24 W	29 ft · 14 ft	46 ft · 22 ft	74 ft · 35 ft
36 W	19 ft · 9 ft	31 ft · 14 ft	49 ft · 23 ft
48 W	14 ft · 7 ft	23 ft · 11 ft	37 ft · 17 ft
60 W	11 ft · 5 ft	18 ft · 8 ft	29 ft · 14 ft

Each pair is Armacost’s limit, then Diode LED’s. The sum: 2 × the amps × the wire’s ohms a foot × the feet, as Armacost’s calculator works it; Diode LED’s own chart gives the same feet.

Four kitchens, measured

An L-shaped kitchen, the Kitchen Renovation Planner’s own: runs of 30, 24, 48 and 60″. 13′ 6″ of Armacost’s 12 V, 60 LEDs/m tape, cut at its 2″ marks with nothing left dark, wired run to run on one leg: 28 W on a 36 W driver, 3,483 lumens. Diode LED’s 200 lumen BLAZE is 39.6 W, which needs its 60 W dimmable driver. On 6 ft of 18 AWG the feed drops 0.18 V and 0.25 V, inside both limits.

A long galley for cooking: runs of 8, 10 and 6 ft, the brightest tape. At 12 V, Armacost’s 120 LEDs/m takes two legs, 8 ft and 16 ft (36 + 48 W): 84 W on a 120 W driver. At 24 V the same tape runs all 24 ft from one end, one leg at 86.4 W. Diode LED’s 300 lumen BLAZE (24 V only) still needs two legs: 108 W on its 150 W driver.

The same L with puck lights about 18″ apart. 9 pucks: 2, 1, 3 and 3 a run. Nine Armacost PureVue (4 W, 375 lumens each) make 36 W, on its 36 W driver, and 250 lumens a foot of counter, close to the 60 LEDs/m tape’s 258. Nine Diode LED TRIANT 2 make 29.7 W, on its 40 W dimmable driver.

The driver over the fridge, 40 ft of wire away. The L’s 28 W loses 1.19 V on 18 AWG, over Armacost’s 0.75 V: use 14 AWG wire (0.47 V) or keep the feed under 25 ft. For Diode LED’s BLAZE, no wire up to 14 AWG stays within 3%; move the driver within 8 ft.

Common mistakes

Sizing the driver from the data sheet’s watts a metre. 16 ft of Armacost’s 12 V, 60 LEDs/m tape at 9 W a metre reads 44 W; its own chart says 28 W is used, because “longer lengths of LED tape will use fewer watts per meter than shorter lengths”.
A 20% buffer, or none, by habit. Follow the driver’s maker. Armacost’s drivers “do not require a 20% de-rating ‘buffer’”; Diode LED’s dimmable driver “should be loaded to 80% maximum (i.e. 80w for 100w model)”.
One leg past the tape’s longest run. Armacost: past it, the “LEDs farthest from the power supply” look dimmer, and “Using a higher wattage power supply will not reduce the effect of voltage drop.” Feed it as two legs, or use 24 V.

Cutting between the marks. Cut “directly in the center of the copper pad”. A tape with far-apart marks leaves the ends dark: Armacost’s 24 V, 30 LEDs/m cuts every 6½″, so a 24″ run lights 19½″.
A long, thin feed. Armacost: “18 gauge or heavier wire is generally recommended. Do not coil excess wire; shorter lengths and thicker wire will mean less voltage drop and higher brightness.”
Two drivers on one run, or 12 V and 24 V mixed. “Never connect more than one power supply to a run of LED lighting.” A second driver takes its own legs.

Under-cabinet lighting: questions people ask

How much LED strip do I need for under-cabinet lighting?

The length of each run of wall cabinets, inside its side panels, cut down to the tape’s marks (1–6½″ apart), added up. The L-shaped kitchen above, runs of 30, 24, 48 and 60″, takes 13′ 6″.

What size driver do I need for under-cabinet LED strip?

One rated for the watts the tape uses, by the driver maker’s rule. Armacost: no buffer, so 28 W takes its 36 W driver. Diode LED’s dimmable driver is loaded to 80%, so 39.6 W takes its 60 W one.

Should I use 12V or 24V under-cabinet lighting?

Either, for most kitchens: 12 V tape at 60 or 120 LEDs/m runs 16.4 ft from one end. Longer than that, 24 V runs twice as far on one leg (32.8 ft), or feed the 12 V tape as two legs.

How many lumens per foot for under-cabinet lighting?

Armacost’s three tapes give 129, 258 and 427 lumens a foot at 12 V, for accent, everyday and task lighting in its own words. Neither maker prints a light level for a counter, so the planner gives lumens.

How far apart should puck lights be under cabinets?

Neither Armacost nor Diode LED prints a spacing, so it is your choice; closer is more even. At about 18″, 375-lumen pucks give about 250 lumens a foot of counter, close to a 60 LEDs/m tape.

What gauge wire for under-cabinet LED lights?

18 gauge or heavier, as Armacost advises, and thicker for a long feed: the drop must stay under 0.75 V at 12 V (Armacost) or 3% (Diode LED). The table above gives the feet for each gauge.

How do I get the lights past a range hood or a window?

Jump the gap with wire. Armacost: “connect a length of wire to the two strips of LED tape light” with its connectors. Count only the tape for the watts and the leg’s length, not the wire.

Can one driver run all my under-cabinet lights?

Yes, if its rating (or 80% of it, for Diode LED’s dimmable one) holds all the watts and no leg is longer than the tape’s longest run. Each leg is wired to the driver; a second driver takes its own legs.

Planning the whole kitchen? The kitchen renovation planner lays out the wall cabinets and hands their runs here, or draw your kitchen in the free 2D planner. Lighting the ceiling too? The recessed lighting and lumens calculator spaces the cans.

Under-Cabinet Lighting Planner