LED Wattage and Lumens Calculator
Convert lumens to watts, size any commercial space to IES light levels, and see your energy savings, payback, and CO2 reduction. Then get a free fixture plan from our team.
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Why LED wattage and lumen conversion matters
For decades you could pick a fixture by watts, because with metal halide, HPS, and fluorescent the wattage roughly tracked brightness. LED breaks that link. A 150-watt LED high bay can out-light a 400-watt metal halide, so sizing a project by the old wattage leads to over-buying fixtures and over-lighting the space. The number that actually matters is lumens, the light delivered to the work surface. This calculator converts between lumens and watts correctly, sizes your space to the recommended light level, and shows the energy, dollars, and CO2 you save by switching. See the methodology.
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How Many Lumens Do You Need?
Size your space to IES light-level targets, or find the LED that replaces your old fixture. Then get a free fixture plan from our team.
Estimates based on IES recommended light levels. We confirm the exact layout with a free photometric plan.
Methodology
How the calculator works
The formulas in plain terms, so you can check the math.
Lumens vs watts
Watts measure the power a fixture draws. Lumens measure the light it produces. Two fixtures can draw the same watts and produce very different light, which is why you size by lumens, not watts.
LED efficacy (lumens per watt)
Efficacy is lumens divided by watts. Go Green LED fixtures run roughly 110 to 170 lm/W. To find the wattage you need: watts = lumens needed / efficacy. Higher efficacy means fewer watts for the same light.
Lumens needed for a space
One foot-candle equals one lumen per square foot. Lumens needed = floor area (sq ft) x target foot-candles, using the IES recommended level for your space (about 25 fc for a warehouse, 30 to 50 for an office). We add a light-loss and fixture-utilization allowance so the real fixture count holds up in the field. Because light mounted higher loses more before it reaches the floor, the calculator lowers that allowance as your ceiling height rises, so a taller space returns more fixtures and, past about 20 feet, points you to a high bay.
Energy cost and savings
Annual cost = fixtures x watts / 1000 x hours per day x days per year x rate ($/kWh). Savings is the old annual cost minus the new. We adjust the old fixture's draw for ballast losses (metal halide adds about 15%, HPS 13%, fluorescent 10%) so the comparison is honest.
CO2 reduction
CO2 avoided = kWh saved x 0.855 lb/kWh (US average delivered grid, EIA and EPA), converted to metric tons.
Why LED drivers affect wattage
Every LED fixture has a driver that consumes a little power, just as the old fixtures had a ballast. We size to the real system wattage, not just the bare LED rating, so the equivalents and savings are not overstated.
Reference
LED wattage conversion chart
Typical wattage that produces a given light output, by technology. Approximate, for quick comparison.
| Light output (lumens) | LED watts | Fluorescent watts | Metal halide / HPS watts |
|---|---|---|---|
| ~5,000 | 35 to 45 W | ~100 W | 100 to 150 W |
| ~10,000 | 75 to 90 W | ~200 W | 175 to 250 W |
| ~16,500 | 120 to 150 W | ~320 W | 250 to 400 W |
| ~24,000 | 175 to 200 W | n/a | ~400 W |
| ~33,000 | 240 W | n/a | ~750 W |
| ~45,000 | 300 W | n/a | ~1,000 W |
Approximate equivalents assuming LED around 120 lm/W, fluorescent around 50 lm/W, and typical HID output before depreciation. Real numbers vary by fixture, optics, and age. Use the calculator above for your exact fixture and rate.
Quick Answers
Common conversions and light-level targets
The conversions we are asked about most, in one place. Use the calculator above for your exact space.
Metal halide and HPS to LED
- 1000W metal halide~300W LED
- 400W metal halide~150W LED
- 250W metal halide / HPS~100W LED
- 150W metal halide~60W LED
A 400W metal halide draws about 460W with its ballast; a 150W LED high bay matches its light and cuts energy roughly two thirds. Approximate, confirm with the calculator.
Lumens per square foot by space
- Warehouse / storage20 to 30
- Office / manufacturing30 to 50
- Retail50 to 100
- Auto / service bay~50
- Parking lot1 to 5
One foot-candle equals one lumen per square foot, so a 30 fc office target is 30 lumens per square foot of floor.
Savings by Industry
What a switch looks like in real spaces
Example retrofits at $0.13/kWh. Your numbers depend on rate, hours, and fixture count, which the calculator works out for you.
Warehouse
100 x 400W metal halide high bays to 150W LED, 12 hours a day. Roughly $15,000 saved per year and about 116,000 kWh, payback in about 16 months.
Office
75 x 4-lamp fluorescent troffers (128W) to 40W LED panels, 10 hours a day. Roughly $2,600 saved per year, payback in about 2.5 years, with better, flicker-free light.
Retail
40 x 250W metal halide to 80W LED, 14 hours a day. Roughly $5,400 saved per year, payback in about 13 months, plus higher color rendering on merchandise.
Parking lot and exterior
20 x 400W metal halide shoebox to 150W LED area lights, dusk to dawn. Roughly $3,200 saved per year, payback in about 1.8 years, with dark-sky-friendly optics.
Customer Results
Real savings from real switches
A sample of what businesses saved in their first year after moving to Go Green LED.
Results vary by facility size, operating hours, and utility rate. Use the calculator above to estimate yours.
The Real Story
Why lumens matter more than watts
LED efficiency. A modern LED turns far more of its watts into usable light than metal halide or fluorescent, so it hits the same light level on a fraction of the power.
Color temperature. A 5000K fixture reads brighter and crisper than a warm 3000K one at the same lumens. The right CCT can let you use less light, not more.
Beam angle. A focused beam puts more of the lumens where you need them. A wide flood spreads the same lumens thinner, so raw lumens alone do not tell the whole story.
Fixture optics. Lenses and reflectors decide how many lumens actually land on the floor instead of scattering. Good optics are why a lower-lumen LED can out-perform a higher-lumen fixture on paper.
For high ceilings, start with our LED high bays. For offices and interiors, see LED troffers and panels.
Common Questions
Lumens, watts, and savings FAQ
How do I convert lumens to watts?
How many lumens do I need for a warehouse?
How much can I save switching to LED?
What is the lifespan of LED fixtures?
Do LEDs reduce heat output?
What LED wattage replaces a 400-watt metal halide?
How many lumens per square foot do I need?
See what your space needs.
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