How Many Metres of LED Strip per Driver? Sizing With 20 % Headroom
A driver is not sized by the metres you ordered, but by the watts those metres draw — and then by the fifth you deliberately leave unused. At 14.4 W/m, a 100 W driver carries about 5.5 m comfortably. The 7 m it says on the label is what it carries in a lab, on a bench, in winter.
Why the 20 %
Three reasons, none of them marketing. A lightbox is a sealed box: a driver working at 100 % inside one sits in its own heat and derates, or fails early. Switch-on draws a brief inrush that a driver at full load has no room for. And cheap drivers do not deliver their rated watts continuously — the 100 W on the case is a peak figure with a tolerance behind it.
Comfortable metres per driver
14.4 W/m strip, 80 % of rated watts
Metres of 14.4 W/m strip per driver, at 80 % load
At 7.2 W/m strip the same drivers carry double: 40 W → 4.4 m, 100 W → 11.1 m. The arithmetic does not change with strip width, only with watts per metre.
The table to keep by the phone
| Driver | 80 % load | 14.4 W/m | 7.2 W/m | Typical job |
|---|---|---|---|---|
| 40 W | 32 W | 2.2 m | 4.4 m | small sign face |
| 60 W | 48 W | 3.3 m | 6.7 m | one small cabinet |
| 100 W | 80 W | 5.6 m | 11.1 m | one 2 m bay |
| 150 W | 120 W | 8.3 m | 16.7 m | a 2 x 3 m box |
| 200 W | 160 W | 11.1 m | 22.2 m | two bays |
Rounded to one decimal. If you are between two drivers, take the larger: the price gap is small, the heat gap is not.
Worked example: a 2 m × 3 m box
Say the layout uses two 3 m runs at 14.4 W/m: 43.2 W each, 86.4 W total. One 100 W driver would run at 86 % — technically inside its rating, practically too hot for a sealed box. Two 60 W drivers, one per run, sit at 72 % each and let you switch the two halves separately. A single 150 W driver at 58 % is the cheapest single-box answer and still leaves room for a third run.
Five ways owners cook a driver
Undersizing by the label. Buying 14 m of strip “because the driver says 100 W”. The strip draws 201 W; the driver runs hot from the first minute.
No air. A driver in a sealed box, in a shop window at 35 °C, is already derating before it is asked to do any work.
Chaining runs. Two jobs hung off one 60 W driver “because it had some left” — the leftover was the headroom, not spare capacity.
Cutting strip live. A live cut shorts the output; a surprising share of the failed drivers we are sent back died on the bench, not on site.
Ignoring the ambient. Sizing on a 25 °C lab when the box sits at 40 °C behind a shop front, where the fan cannot help.
Frequently Asked Questions
Can one driver feed two separate faces?
Yes, wired in parallel, as long as the total load stays inside the 80 % figure and both runs are the same voltage and same strip. Parallel is what keeps one face from dimming the other; series wiring of constant-voltage strip is not something to attempt.
Do I need a bigger driver for 12 V?
The watts are the same, so the driver rating does not change — but the current doubles, which is why 12 V runs need thicker cable and shorter lengths (see our voltage-drop note). Above about 4 m, 24 V is the cheaper answer overall.
Waterproof or indoor driver?
Match it to where the driver actually sits. Inside a dry lightbox an indoor driver is fine and cheaper; on a wet site, or anywhere condensation forms, use the sealed version and keep the enclosure ventilated.
Send us the face size and the strip you plan to use — we will come back with the run split, the driver rating and the cable gauge. See our constant-voltage LED drivers.
Products referenced
constant-voltage LED drivers, IP20 / IP65 · lightbox power supplies and wiring options