Quick answer
Lumens needed = room area × target foot-candles. A 200 ft² room at 30 foot-candles needs 6,000 lumens in total.
Enter the room area and the target light level. The calculator returns the total lumens needed. It tells you how many lumens of lighting a room needs.
Related tools: Appliance Energy Cost Calculator: Electricity cost of running an appliance. Pool Fill Time Calculator: Hours to fill a pool at a flow rate. Room Area Calculator: Floor area of a rectangular room.
How to use the Lighting Lumens Calculator
- Enter room area (ft²) (above 0).
- Enter target light level (foot-candles) (above 0).
- Optionally, enter lamp efficacy (optional) (lm/W) (above 0).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Room area | A number, in ft² | > 0 |
| Target light level | A number, in foot-candles. 1 foot-candle = 1 lumen per ft²; recommended levels depend on the task | > 0 |
| Lamp efficacy (optional) (optional) | A number, in lm/W | > 0 |
Formula and method
Formula
lumens = area × foot-candles
IEEE-754 double precision; shown to the decimals indicated.
1 foot-candle equals 1 lumen per square foot. Recommended levels depend on the use of the room.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Room area = 200; Target light level = 30.
| Result | Value |
|---|---|
| Lumens needed | 6,000 lumens |
| Electrical power needed | — |
Example 2
Inputs: Room area = 150; Target light level = 50; Lamp efficacy (optional) = 80.
| Result | Value |
|---|---|
| Lumens needed | 7,500 lumens |
| Electrical power needed | 93.8 W |
Example 3
Inputs: Room area = 400; Target light level = 20; Lamp efficacy (optional) = 100.
| Result | Value |
|---|---|
| Lumens needed | 8,000 lumens |
| Electrical power needed | 80 W |
The first line is the headline result (lumens needed). Below it the lighting Lumens Calculator lists electrical power needed, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Foot-candles by room
Recommendations vary by task: about 10 to 20 foot-candles for living areas and hallways, 30 to 50 for kitchens and bathrooms, and 50 or more for detailed tasks like reading or workshops.
From lumens to bulbs
Divide total lumens by the lumens per bulb. A 800-lumen bulb (about 60 W equivalent) means 7.5, so eight bulbs would be needed for 6,000 lumens. Walls, colours and fixtures affect how much light reaches the work surface.
How the result changes with room area
Holding every other input at the first worked example, this table changes only room area. It shows how sensitive the answer is to that one value; each row was produced by running this calculator.
| Room area | Lumens needed | Electrical power needed |
|---|---|---|
| 100 | 3,000 lumens | — |
| 200 | 6,000 lumens | — |
| 400 | 12,000 lumens | — |
| 800 | 24,000 lumens | — |
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Room area: entering "0" shows "Room area must be greater than 0." beside that field and no result.
- Target light level: entering "0" shows "Target light level must be greater than 0." beside that field and no result.
Choosing between the Lighting Lumens Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Appliance Energy Cost Calculator](/lifestyle/appliance-energy-cost-calculator/) | power, hours used per day and electricity price | Cost per day |
| [Pool Fill Time Calculator](/lifestyle/pool-fill-time-calculator/) | pool volume and flow rate | Fill time |
| [Room Area Calculator](/lifestyle/room-area-calculator/) | length and width | Room area |
| [Wall Area Calculator](/lifestyle/wall-area-calculator/) | room length, room width and ceiling height | Wall area |
| [Water Bill Calculator](/lifestyle/water-bill-calculator/) | water used, rate per unit and fixed monthly charge | Estimated bill |
Assumptions and limitations
- Fixtures lose some light
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for room area and target light level to confirm this.
Frequently asked questions
What is a foot-candle?
One lumen per square foot.
How do I convert to lux?
Multiply foot-candles by 10.764.
Does bulb type matter?
Lumens matter, not watts.
What does the Lighting Lumens Calculator calculate?
Lumens needed for a room at a light level you choose. It returns Lumens needed and Electrical power needed.
What formula does the Lighting Lumens Calculator use?
lumens = area × foot-candles. 1 foot-candle equals 1 lumen per square foot.
What do I need to enter in the lighting Lumens Calculator?
You enter Room area (ft²) and Target light level (foot-candles). Optional: Lamp efficacy (optional) (lm/W).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Fixtures lose some light.
What is an example of a lighting Lumens result?
With room area 200 and target light level 30, the lumens needed is 6,000 lumens.
Where does the method come from?
The method follows: Definition of the foot-candle (1 lm/ft²).
Related calculators
- Appliance Energy Cost Calculator — Electricity cost of running an appliance.
- Pool Fill Time Calculator — Hours to fill a pool at a flow rate.
- Room Area Calculator — Floor area of a rectangular room.
- Wall Area Calculator — Wall area of a rectangular room after openings.
- Water Bill Calculator — Water bill from usage, rate and a base charge you enter.
- Water Usage Calculator — Household water use from people and use per person.
Sources
- Definition of the foot-candle (1 lm/ft²)
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.