To find how many LED high bay lights you need, use this formula: fixtures = (square footage × footcandles × light loss factor) ÷ fixture lumens. For a 10,000 sq ft warehouse needing 30 footcandles with 30,000-lumen fixtures, that is (10,000 × 30 × 1.5) ÷ 30,000 = 15 fixtures. Most 10,000 sq ft warehouses need 12 to 20, depending on brightness, ceiling height, and fixture output.
Most people get a smaller number than they should, and the reason is one multiplier almost everyone forgets. Skip it and your room looks fine on paper but comes up dim in real life.
High Bay Count at a Glance:
The formula is square footage times footcandles times light loss factor, divided by fixture lumens. Always round up. The light loss factor (1.3 to 1.5) is the step people miss, and it is what keeps the room bright as fixtures age and gather dust.
What Is the LED High Bay Lighting Formula?
The math is simple once you have four numbers: your floor area, the brightness the space needs (in footcandles), a light loss factor, and the lumens each fixture puts out.
Fixtures = (square footage × footcandles × light loss factor) ÷ fixture lumens
Footcandles measure how much light lands on the floor, so a workshop needs more than a storage aisle. If the lumen and footcandle terms are new, our guide on what a lumen is explains the basics in plain words.
How Many Footcandles Does Your Space Need?
Brightness need depends on the task. Fine inspection work wants far more light than a storage room. Use this as your starting point.
Space Type | Footcandles | Fixtures per 1,000 sq ft |
|---|---|---|
Warehouse / storage | 20 to 30 | 1 to 2 |
Manufacturing / assembly | 30 to 50 | 2 to 3 |
Detailed assembly / inspection | 50 to 100 | 3 to 5 |
Auto repair shop | 50 to 75 | 3 to 4 |
Retail / showroom | 50 to 75 | 3 to 4 |
Gym / sports facility | 30 to 50 | 2 to 3 |
How Do You Calculate Fixture Count Step by Step?
Measure the floor area. Length times width for a rectangle. For odd shapes, split into rectangles and add. Subtract enclosed offices or restrooms that light themselves.
Pick a footcandle target. Use the chart above, leaning higher for detailed work. When unsure, aim for the middle of the range, since you can dim later.
Apply the light loss factor. Multiply by 1.3 to 1.5. This covers fixtures dimming with age, dust on the lenses, and dark walls soaking up light. Clean, bright rooms use 1.3, dusty or dark ones use 1.5.
Divide by fixture lumens. Divide the total by one fixture's output, then round up. For 20,000 sq ft at 50 fc with 36,000-lumen fixtures: (20,000 × 50 × 1.4) ÷ 36,000 = 38.9, so 40 fixtures.
Always round up. Too few fixtures leaves dark gaps between them that hurt safety and productivity.
How Should You Space and Lay Out High Bay Lights?
Getting the count right is only half the job. Even spacing is what stops bright pools under each light and shadows in between.
Space fixtures at 1.0 to 1.5 times the mounting height. At a 20-foot ceiling, that is 20 to 30 feet apart. Tighter spacing (1.0x) gives the most even light, while wider spacing (1.5x) uses fewer fixtures but shows more variation.
Lay them in a grid. For a 100 by 200 foot warehouse at 25-foot spacing: 100 ÷ 25 = 4 rows, 200 ÷ 25 = 8 columns, so 32 fixtures. Offset the first row from the wall by half the spacing, about 12.5 feet, so the edges are not dim. In racked warehouses, align fixtures over the aisles, not the rack tops.
How Does Mounting Height Change the Fixture You Need?
Higher ceilings need brighter fixtures, because light fades fast with distance. High bays suit ceilings of 15 to 45 feet, and the right wattage climbs with height.
Mounting Height | Fixture | Lumens |
|---|---|---|
15 to 20 ft | 150W | ~22,000 |
20 to 30 ft | 200 to 240W | 30,000 to 36,000 |
Above 30 ft | 300W+ | 45,000+ |
Planning a warehouse fit-out? See our picks for the best LED warehouse lights to match these numbers to real fixtures.
Conclusion:
Sizing high bay lighting comes down to floor area, footcandles, the light loss factor, and fixture lumens. Run the formula, round up, space fixtures at 1 to 1.5 times the ceiling height, and match wattage to your mounting height for bright, even light with no dark spots.
(FAQs):
Q1. How many LED high bays for a 5,000 sq ft workshop?
A: About 12. At 50 footcandles with 30,000-lumen fixtures: (5,000 × 50 × 1.4) ÷ 30,000 = 11.7, rounded to 12, in a 3 by 4 grid roughly 20 feet apart. A home garage of 400 to 600 sq ft needs just 2 to 4.
Q2. Can you use too many high bay lights?
A: Yes. Too much light wastes power and causes glare and eye strain. The smart way to add extra is dimmable fixtures with sensors, so you get even coverage and headroom but dim to the right level. For a garage, see the best LED garage lights.
Q3. Should you use 150W or 200W high bays?
A: It depends on height. At 15 to 20 feet, 150W fixtures are plenty. At 20 to 30 feet or wider spacing, step up to 200W. Fewer high-wattage fixtures cost less to install, but more low-wattage ones give more even light.
Q4. What is the light loss factor and why does it matter?
A: It is a multiplier of 1.3 to 1.5 that accounts for fixtures dimming over time, dust, and dark surfaces. Skip it and you install too few lights, leaving the space dimmer than planned once real-world losses set in.
