How Many LED Cabinets and Amps for a 20 m² Wall?

Two questions arrive with almost every 20 m² enquiry: how many cabinets that buys, and what it draws. Both are arithmetic on numbers already printed on the datasheet, and both are routinely answered from the wrong column. Here is the full calculation, using our own cabinet dimensions and power figures, so it can be checked against any other quote.

Area decides the cabinet count. Pitch never does.

A cabinet is a box of a fixed size. The pitch decides how many LEDs sit inside it, not how large it is. So for a given square metreage the box count is identical whether the order is P2.5 or P3.91 on the same cabinet — worth holding on to when a supplier quotes "more cabinets" because the pitch is finer.

• Outdoor, 1000 × 1000 mm — 1.00 m² per cabinet, 26 kg
• Stadium, 960 × 960 mm — 0.92 m² per cabinet, 28 kg
• Rental, 500 × 1000 mm — 0.50 m² per cabinet, 11 kg indoor or 15.5 kg sealed
• Indoor 16:9, 600 × 337.5 mm — 0.20 m² per cabinet, 4.8 kg
• Indoor 4:3, 640 × 480 mm — 0.31 m² per cabinet, 6 kg
• Indoor 8:9, 480 × 540 mm — 0.26 m² per cabinet, 6.1 kg
• Poster, 640 × 1920 mm — 1.23 m², 48 kg, sold as a unit

The same 20 m², built six ways

Rounded up to whole cabinets, and to a layout that does not leave a part cabinet at the edge:

• Outdoor — 20 cabinets, 5 × 4, exactly 20.00 m², finished size 5.0 × 4.0 m
• Stadium — 22 cabinets is 20.28 m², but the grid that ships is 6 × 4 = 24 cabinets, 22.12 m², 5.76 × 3.84 m
• Rental — 40 cabinets, 10 × 4, exactly 20.00 m², 10.0 × 4.0 m
• Indoor 16:9 — 99 cabinets, 11 × 9, 20.05 m², 6.60 × 3.04 m
• Indoor 4:3 — 65 cabinets, 13 × 5, 19.97 m², 8.32 × 2.40 m
• Indoor 8:9 — 77 cabinets, 7 × 11, 19.96 m², 3.36 × 5.94 m

Two things fall out of that list. A 20 m² indoor wall is between 65 and 99 cabinets, not twenty — small cabinets mean more boxes, more seams and more installation time for the same area. And the outdoor and rental formats land on 20.00 m² with a clean grid, which is why quotes in those formats tend to come out on round numbers while indoor quotes do not.

What the same 20 m² actually resolves

Pixels are area divided by pitch squared, so the pixel count rises with the square of the pitch difference. On a 5.0 × 4.0 m wall:

• P6.25 — 800 × 640, 512,000 pixels
• P4 — 1,250 × 1,000, 1.25 million pixels
• P3.91 — 1,279 × 1,023, 1.31 million pixels
• P2.976 — 1,680 × 1,344, 2.26 million pixels
• P2.5 — 2,000 × 1,600, 3.2 million pixels
• P1.875 — 2,667 × 2,133, 5.69 million pixels

This is what a finer pitch actually buys at a fixed area: more LEDs, more driver channels, more cost per square metre — and a picture that survives a viewer standing closer. It does not buy more cabinets.

The average column pays the bill. The maximum sizes the circuit.

Every datasheet carries two power figures and they answer different questions. Average is what the wall draws over a working day, and it belongs in the energy calculation. Maximum is what it draws with every LED at full white and brightness at 100 percent, and it is the only figure a breaker, cable, generator or UPS should be sized on.

• Indoor 16:9 — 220 W/m² average, 650 W/m² maximum
• Indoor 4:3 — 170 W/m² average, 500 W/m² maximum
• Indoor 8:9 — 220 W/m² average, 650 W/m² maximum
• Rental 500 × 1000 — 260 W/m² average, 800 W/m² maximum
• Outdoor — 265 W/m² average, 800 W/m² maximum
• Stadium — 300 W/m² average, 900 W/m² maximum

The poster is the exception: 640 × 1920 is quoted at 265 W average and 800 W maximum per unit, not per square metre, because it is sold as one piece. Mixing the two conventions is the single most common error in a poster quote.

A worked example: 20 m² of outdoor at P4

20 m² at 265 W/m² average is 5,300 W. At 800 W/m² maximum it is 16,000 W. On a 400 V three-phase supply, before power factor, 16,000 W is 23.1 A per phase. On 230 V single phase it is 69.6 A. Those are the two numbers that decide whether the site needs one circuit or three.

• Step 1 — multiply area by the maximum column, not the average: 20 × 800 = 16,000 W
• Step 2 — divide by the supply: 400 V three-phase gives 16,000 ÷ (1.732 × 400) = 23.1 A per phase; 230 V single phase gives 16,000 ÷ 230 = 69.6 A
• Step 3 — divide again by the driver power factor from the PSU datasheet. It is below 1, so the real current is higher than the figure above
• Step 4 — apply the continuous-load rule the local code uses; commonly the circuit is rated at 125 percent of the load, which turns 23.1 A into about 29 A and a 32 A breaker
• Step 5 — add the controller, the video processor and any cooling. Small next to the wall, but not zero

Run the same five steps on an indoor 20 m² wall at 650 W/m² maximum — 13,000 W — and a single 230 V circuit is out of the question at 56.5 A. That is the practical reason indoor walls are usually quoted with two or three supplies rather than one.

Six things the datasheet does not tell you

• Power factor. It is a property of the driver, not the panel, and it decides how much of the current is real
• Inrush. A wall of switching supplies draws a spike at power-on that a thermal breaker tolerates and a fast electronic trip may not
• Dimming headroom. Indoor walls normally run well below 100 percent brightness, which is why average sits so far under maximum
• Voltage drop. A long run from the board to the wall changes the cable size, not the wall
• Binning. Cabinets from different production runs can differ slightly in colour, so order the spares in the same bin as the wall
• Structure. 20 m² of outdoor cabinet is 520 kg of panel before frame and ballast; the fixing question usually arrives after the power question

What to send instead of a question

Four numbers get a wall specified in one exchange: the finished width and height, or the area; the distance to the nearest viewer; the supply available on site, single or three phase and in amps; and whether the wall is indoors, outdoors or touring. Pitch, cabinet, brightness and protection all follow from those four.

The short version

• Cabinet count comes from area and cabinet size, never from pitch
• 20 m² is 20 outdoor cabinets, 40 rental cabinets, or 65 to 99 indoor cabinets depending on format
• Size the circuit on the maximum column and the driver power factor; cost the energy on the average
• Poster power is per unit, not per square metre — do not mix the two
• A finer pitch at the same area multiplies pixels and cost; it does not change the box count