Watt to Lumen Calculator
Convert watts (W) to lumens (lm): lm = W × η (lm/W). Free online tool — no sign-up. Clear formulas and worked examples. Runs locally in your browser.
Trust summary Engine tested · Specification checked · v1.1.0
- Input interpretation
- Enter values to calculate.
- Result
- —
- Model
- Luminous flux, electrical power, or luminous efficacy from any two of W, lm, and η.
- Scope
- η is constant for the chosen lamp / operating point
- Verification
- Engine tested · Specification checked · v1.1.0
- Named expert review
- Optional · Not performed
- Specification basis
- Φ (lm) = P (W) × η (lm/W)
Formulas
Core equations used by this calculator.
How to use
Choose direction
W → lm for brightness from wattage, lm → W for power from lumens, or η = lm ÷ W.
Enter watts (or lumens) and efficacy
Use package lm/W when listed, or a typical value for the lamp type.
Read lumens, watts, or efficacy
Shop by lumens for brightness; use watts for energy use.
Example calculations
Common configurations with formula and result.
10 W · LED 100 lm/W
Default
9 W · LED 90 lm/W
~60 W equivalent
60 W · incandescent 14 lm/W
Classic bulb
5 W · LED 90 lm/W
~40 W equivalent
16 W · LED 100 lm/W
~100 W equivalent
lm → W
800 lm · 90 lm/W
Typical luminous efficacy (guide)
Common values at a glance.
| Light source | Approx. η (lm/W) | Notes |
|---|---|---|
| Incandescent (tungsten) | 12–18 | Often ~13–15 |
| Halogen | 16–30 | — |
| CFL / fluorescent | 40–75 | Often ~55–60 compact |
| LED | 80–120+ | Often ~90–100 for lamps |
| Metal halide | 75–100 | HID |
| High-pressure sodium | 85–150 | Street / industrial |
Watt to Lumen calculator specification
Version 1.1.0 · Engine tested
- Engine tested 4 published cases
- Named expert review Not performed
- Calculation version 1.1.0
- Definition
- Watts (W) measure electrical power; lumens (lm) measure visible light output. Luminous efficacy η (lm/W) links them: lm = W × η and W = lm ÷ η. Higher η means more light per watt — a 9 W LED can match a 60 W incandescent in lumens.
- What it calculates
- Luminous flux, electrical power, or luminous efficacy from any two of W, lm, and η.
- Inputs
- Any two of: watts (W), lumens (lm), efficacy η (lm/W)
- Outputs
- Lumens, watts, or efficacy (lm/W)
- Formula
Φ=P·η; P=Φ/η; η=Φ/P- Assumptions
- η is constant for the chosen lamp / operating point
- Units
- W, lm/W → lm
- Boundary conditions
- η = 0 → undefined on lm → W (UI returns 0)
- Example
- 10 W, 100 lm/W → 1000 lm
- Validation cases
4 published on this page
- 10 W, 100 lm/W → 1000 lm
- 9 W, 90 lm/W → 810 lm
- 800 lm, 90 lm/W → W → ≈ 8.8889 W
- 800 lm, 9 W → η → ≈ 88.8889 lm/W
- Specification basis
- Φ (lm) = P (W) × η (lm/W)
- Calculation version
- 1.1.0
Background
Interpretation and common distinctions.
Convert watts (W) to lumens (lm) using luminous efficacy eta in lm/W.
Phi((lm)) = P((W)) × eta((lm/W)) P((W)) = (Phi((lm)))/(eta((lm/W)))
Default: 10 W · 100 lm/W → 1000 lm (typical LED-class estimate).
Watts vs lumens
| Quantity | Unit | Meaning |
|---|---|---|
| Power | W | How much electricity the lamp draws |
| Luminous flux | lm | How much visible light it emits |
| Luminous efficacy | lm/W | Light per watt — efficiency of making visible light |
Shop by lumens for brightness; use watts for energy use and circuit loading.
Brightness examples (approximate)
| Target brightness | Typical LED | Typical incandescent |
|---|---|---|
| ~450 lm | ~5 W | ~40 W |
| ~800 lm | ~9 W | ~60 W |
| ~1600 lm | ~16 W | ~100 W |
Exact wattage depends on the product’s rated η (often ~90–100 lm/W for LED, ~13–15 lm/W for incandescent).
Related tools
Other calculators in this family: Lumen to Watt, Watt to Lux, Lumen to Lux, Watts to Amps .
Frequently asked questions
Key distinctions behind the calculation.
How do I convert watts to lumens?
Multiply by luminous efficacy: lm = W × η (lm/W). Example: 10 W × 100 lm/W = 1000 lm.
What is luminous efficacy?
How many lumens you get per watt of electrical power (lm/W). Higher efficacy = more light for the same electricity.
Are watts and lumens the same?
No. Watts are power; lumens are visible light output. LEDs deliver similar lumens at much lower watts than old incandescent bulbs.
How many lumens is a 60 W bulb?
A classic 60 W incandescent is often ~700–900 lm (roughly 800 lm). An LED making ~800 lm usually draws about 8–10 W.
What LED replaces a 40 W / 60 W / 100 W bulb?
Match lumens: ~450 lm (~5 W LED), ~800 lm (~9 W LED), ~1600 lm (~16 W LED) are common approximations — check the package.
What efficacy should I enter for LED?
Use the package value if available. Otherwise start near 90–100 lm/W for common LED lamps.
Can I find efficacy from watts and lumens?
Yes: η = lm ÷ W. Example: 800 lm ÷ 9 W ≈ 88.9 lm/W.
Why do replacement charts disagree?
Efficacy ranges and marketing “equivalents” differ by brand. Prefer stated lumens over watt-equivalent claims alone.