# Lighting Energy Calculator

> Lighting Energy: kWh = fixtures × watts × hours per day × days ÷ 1,000. Methodology stated, your own inputs only.

Page: https://freecalculator.tech/tools/lighting-energy-calculator
Last reviewed: 2026-10-20

## Formula

kWh = fixtures × watts × hours per day × days ÷ 1,000. Cost = kWh × price.

- Methodology: energy = power × time (OpenStax College Physics, power).
- Use system watts including the driver or ballast.
- Dimming and occupancy controls reduce hours or watts — enter the effective figures.
- kWh = fixtures × watts × hours per day × days ÷ 1,000. Cost = kWh × price.
- Inputs used: Currency (symbol only, never converted), Number of fixtures, Power per fixture incl. driver, Hours on per day, Days in the period, Your energy price per kWh (blank = energy only).

## Inputs

- Currency (symbol only, never converted)
- Number of fixtures
- Power per fixture incl. driver
- Hours on per day
- Days in the period
- Your energy price per kWh (blank = energy only)

## Worked example: An office floor

120 fixtures at 36 W, 10 hours a day, 250 days.
1. 120 × 36 = 4.32 kW.
2. 4.32 × 10 × 250 = 10,800 kWh.

## Common questions

### Why isn't an electricity or fuel price filled in?

Prices differ by country, supplier, tariff and time of use, so there is no universal figure. Enter the rate from your bill or contract, or pick a dated saved rate if one is listed on the page.

### Lamp or system watts?

System watts — the lamp plus its driver or ballast — from the product data sheet. Check the formula, example, and limitations on this page before using the result for a real facilities decision.

### How do controls fit in?

Reduce the hours (occupancy sensors) or watts (dimming) to the effective average. Check the formula, example, and limitations on this page before using the result for a real facilities decision.

### How do I use the Lighting Energy Calculator?

Enter the required values for Currency (symbol only, never converted), Number of fixtures, Power per fixture incl. driver, Hours on per day, Days in the period, and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Lighting Energy Calculator use?

kWh = fixtures × watts × hours per day × days ÷ 1,000. Cost = kWh × price. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.

### Can the Lighting Energy Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Uniform hours for every fixture.
- No cooling-load interaction.
- Results are estimates built only from the figures you enter. No electricity, fuel or gas price, equipment efficiency or benchmark is built in — tariffs vary by supplier, region and time, and equipment data must come from the manufacturer. Designs and installations must be checked by a qualified professional.
- The result depends on the values you enter for this lighting energy calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- OpenStax — https://openstax.org/books/college-physics-2e/pages/7-7-power

## Cite this page

- APA: Free Calculator. (2026, October 20). Lighting Energy Calculator. https://freecalculator.tech/tools/lighting-energy-calculator
- MLA: "Lighting Energy Calculator." Free Calculator, 20 Oct. 2026, https://freecalculator.tech/tools/lighting-energy-calculator.
- Link: Lighting Energy Calculator — Free Calculator, https://freecalculator.tech/tools/lighting-energy-calculator