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All calculatorsMethodology

Lumens to Watts Calculator

Convert watts to lumens or lumens to watts using the luminous efficacy on the bulb label, then compare yearly energy use and cost against another bulb type.

Interactive calculator · Method LUMENS-WATTS-1.0 · Last reviewed: 2026-11-04

Calculate your scenario

Lumens = watts × luminous efficacy (lm/W); watts = lumens ÷ efficacy.

Your inputs

Try an example

Default worked example. Edit the inputs to calculate your scenario.

Default worked example

Light output 840 lm
Power draw 60 W
Energy per year 65.7 kWh
Annual energy cost $9.86
Watts for same lumens at comparison efficacy 9.33 W at 90 lm/W
Annual saving with comparison bulb $8.32 (55.48 kWh)

60 W × 14 lm/W = 840 lm; 60 W × 3 h × 365 ÷ 1,000 = 65.7 kWh a year.

How to use the calculator

Choose the direction, enter watts or lumens, pick the current bulb type (or custom with the label efficacy), the bulb to compare with, daily hours and your electricity price.

What the result means

A 60 W bulb at an example 14 lm/W gives about 840 lm; an example 90 lm/W LED needs about 9.33 W for the same light, saving about $8.32 a year at 3 hours a day and $0.15/kWh.

Formula and units

Lumens = watts × luminous efficacy (lm/W); watts = lumens ÷ efficacy. Yearly energy = watts × hours per day × 365 ÷ 1,000 kWh, and cost = kWh × your electricity price. The comparison bulb needs lumens ÷ its efficacy watts for the same light, and the saving is the difference in yearly cost.

Worked examples

60 W incandescent compared with LED: Watts or lumens to convert: 60 W or lm; Custom efficacy for current bulb (from label): 100 lm/W; Custom efficacy for comparison bulb (from label): 120 lm/W; Hours on per day: 3 h/day; Electricity price (example): 0.15 $/kWh; Conversion: w2l; Current bulb efficacy: inc; Comparison bulb efficacy: led.
Example result: Light output: 840 lm; Power draw: 60 W; Energy per year: 65.7 kWh; Annual energy cost: $9.86; Watts for same lumens at comparison efficacy: 9.33 W at 90 lm/W; Annual saving with comparison bulb: $8.32 (55.48 kWh).

1,600 lm LED at 110 lm/W versus halogen: Watts or lumens to convert: 1600 W or lm; Custom efficacy for current bulb (from label): 110 lm/W; Custom efficacy for comparison bulb (from label): 120 lm/W; Hours on per day: 5 h/day; Electricity price (example): 0.22 $/kWh; Conversion: l2w; Current bulb efficacy: custom; Comparison bulb efficacy: hal.
Example result: Light output: 1,600 lm; Power draw: 14.55 W; Energy per year: 26.55 kWh; Annual energy cost: $5.84; Watts for same lumens at comparison efficacy: 88.89 W at 18 lm/W; Annual saving with comparison bulb: -$29.85 (-135.68 kWh).

Limitations and common mistakes

There is no universal watts-to-lumens factor: efficacy varies by product, color temperature and driver, so use the lumens and watts on the actual label (lm ÷ W). The preset efficacies are rough examples only. Brightness perception, beam angle and color quality are not modeled; electricity price is your own entry.

Buying by the “60 W equivalent” wording instead of the lumen figure; compare lumens directly.

Sources and assumptions

Method LUMENS-WATTS-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.