How to Size an LED Driver for Linear Lighting

Short answer

Multiply the lit length by the product’s watts per foot to get the connected load, then choose a driver rated so the load is no more than about 80% of the driver’s rated output (divide the load by 0.8). If one driver cannot carry it, split the run into zones with one driver each. For constant-voltage (24V or 48V) systems, also check voltage drop on the secondary wiring and the product’s maximum run per feed.

Key takeaways

Load (W) = lit length (ft) × W/ft.

Minimum driver rating (W) = load ÷ 0.8 (about 20% headroom).

Class 2 drivers are power-limited (typically 100 W per output; check the driver’s rating), so long low-voltage runs usually need several drivers.

Match the driver’s output type (constant voltage or constant current) and dimming protocol to the fixture.

Step 1: work out the connected load

load (W) = lit length (ft) × power (W/ft)

Use the lit length, not the housing length: end caps and unlit sections draw no power. If the product lists watts per metre, 1 ft = 0.3048 m.

Step 2: add headroom

minimum driver rating (W) = load (W) ÷ 0.8

This keeps the driver at or below about 80% of its rating. Where the manufacturer states a different maximum loading, use theirs.

Step 3: split into zones

A zone is the part of the run one driver powers. You need more than one zone when:

the load exceeds the largest suitable driver;
you are using Class 2 drivers, which are power-limited (typically 100 W per output; check the driver’s rating);
the product’s maximum run per feed is shorter than the run;
voltage drop on the low-voltage wiring would be too high (see 24V vs 48V).

Worked example 1: 24V linear in a cove, remote drivers

A 40 ft cove, 4.5 W/ft, 24V constant-voltage product, 96 W Class 2 drivers.

Step	Calculation	Result
Load	40 ft × 4.5 W/ft	180 W
Usable per driver	96 W × 0.8	76.8 W
Drivers needed	180 ÷ 76.8 = 2.34 → round up	3 drivers
Zones	40 ft ÷ 3	about 13 ft 4 in each, 60 W per driver (63% loaded)

Check the product’s maximum run per feed is at least 13 ft 4 in, then check voltage drop on each driver’s secondary wiring.

Worked example 2: suspended run with integral drivers

A 32 ft suspended run built from four 8 ft sections, 5 W/ft, one integral driver per section.

Step	Calculation	Result
Load per section	8 ft × 5 W/ft	40 W
Driver per section	chosen by the manufacturer for that section	e.g. a 50 W driver, 80% loaded
Total circuit load	4 × 40 W, plus driver losses	about 160 W plus losses (check input watts on the cut sheet)

With integral drivers the fixture manufacturer sizes the driver; your job is to check the input watts per section against the branch circuit and to confirm the driver’s dimming protocol.

Common mistakes

Sizing to 100% of the driver rating.
Using housing length instead of lit length.
Forgetting that several short runs on one driver may add up past its rating.
Mixing constant-voltage products with constant-current drivers.
Choosing a driver that does not support the project’s dimming protocol.

Frequently asked questions

Why not load a driver to 100%?

Drivers run hotter and age faster near full load, and real loads can be slightly higher than nominal. Loading to about 80% leaves margin for tolerance and heat. Some manufacturers publish their own maximum loading; follow it where it differs.

Constant voltage or constant current?

Match the fixture. LED tape and many flexible products are constant voltage (24V or 48V). Many linear fixtures with integral drivers use constant-current LED boards, and the driver is chosen by the fixture manufacturer. Never mix the two.

Does dimming change the driver size?

No, size for full output. But the driver must support the dimming protocol in the controls spec (0-10V, DALI, phase), and its minimum load may matter when very short runs are on one driver.

How to size an LED driver for linear lighting