Watts to lumens calculator for replacing a bulb or lighting a room

How to go from watts to lumens

A 60-watt incandescent bulb is replaced by an LED of 800 lumens: that is the ENERGY STAR chart, which also gives 450 lumens for 40 W, 1,100 for 75 W and 1,600 for 100 W. Between two rows the calculator draws a straight line; below 40 W and above 150 W it goes in proportion. In metric units it uses the EU chart instead, where 60 W means 806 lumens, the figure printed on European boxes.

GU10 halogen spotlights follow a different row, the PAR16 reflector lamps of EU Regulation 1194/2012, which count the light inside a 90° cone: a 50 W spot equals 300 lumens, much less than a 50 W household bulb.

LED watts are lumens ÷ efficacy. The calculator uses 90 lumens per watt, taken from the FTC example (800 lumens for about 9 watts); under advanced options you can enter the efficacy of the bulb in your hand, which is its lumens divided by its watts.

For a room, start from the light level. A foot-candle is one lumen per square foot, so foot-candles × square feet = total lumens; then total lumens ÷ lumens per bulb, rounded up.

A worked example: a 60 W bulb and a 15 × 12 ft living room

The calculator opens with one 60 W A19 bulb with an E26 base, on 3 hours a day.

• Equivalent: 60 W = 800 lumens
• LED: 800 ÷ 90 = 8.9 W, so a 60 W equivalent LED of about 9 watts
• Before: 60 × 3 × 365 ÷ 1,000 = 65.7 kWh a year
• After: 9.73 kWh a year
• Savings: 56 kWh a year for each bulb

At an example price of $0.15 per kWh that is $8.40 a year per bulb; use the rate on your bill.

Pick "Living room" and a 15 × 12 ft room: 20 foot-candles × 180 sq ft = 3,600 lumens. With 60 W equivalent bulbs (800 lumens) you need 3,600 ÷ 800 = 4.5, so 5 A19 LED bulbs of 800 lumens, which save 280 kWh a year against five incandescent bulbs.

In the UK, with metric units, the same 60 W bulb becomes an E27 LED of 806 lumens and about 9 W, and a 5 × 4 m living room at 200 lux needs 4,000 lumens, again 5 bulbs.

Watts to lumens chart

Old bulb	Lumens (US)	LED at 90 lm/W
40 W	450	5.0 W
60 W	800	8.9 W
75 W	1,100	12.2 W
100 W	1,600	17.8 W
150 W	2,600	28.9 W

Light levels used for rooms, from the IES values quoted by Penn State: 20 foot-candles in living rooms and bedrooms (range 10-20), 40 in kitchens (30-40 general), 30 in bathrooms (20-50), 50 in a home office (20-50, about 50 for reading). With 800-lumen bulbs a 12 × 12 ft bedroom needs 4, a 12 × 10 ft kitchen 6, an 8 × 6 ft bathroom 2 and a 10 × 10 ft home office 7.

Bases and lumens on the box

Look for lumens first, then the base. In the US the standard screw base is E26 (medium), found on A19 bulbs in lamps and ceiling fixtures; E12 is the small candelabra base of chandeliers and sconces; GU10 has two pins with wide heads and fits recessed spotlights. In Europe the same bases are E27 and E14. ENERGY STAR notes that boxes often show the equivalent wattage next to the lumens, as in "60 watt replacement".

Foot-candles and lux are the light that reaches the floor or the countertop. Shades, frosted glass and dark walls hold some of it back: pick a bigger bulb size or raise the light level under advanced options. Kitchen counters and bathroom mirrors usually get their own task light on top.

Common mistakes

• Shopping by watts. Two 9 W LEDs can give very different light: the lumen count is what matters.
• Using the household bulb chart for spotlights. A 50 W halogen spot gives less light than a 50 W bulb, because it focuses it into a cone.
• Counting one bulb per fixture. A five-arm chandelier with 450-lumen bulbs gives 2,250 lumens, not 450.
• Forgetting hours of use. Savings grow with the hours: a closet light on half an hour a day saves little, the living room lamp on every evening saves much more.
• Mixing up bases. E26 and E12 do not swap, and some recessed GU10 cans have little room behind: check the length of the LED.