# Light Bulb Calculator

Calculate recommended lumens, LED wattage, and number of bulbs for any room. Enter room size and type to get proper lighting recommendations.

## What this calculates

Is your room too dim or too bright? Enter the room dimensions and type, and this calculator tells you exactly how many lumens you need, the LED wattage to achieve it, and how many standard bulbs that translates to.

## Inputs

- **Room Length** (ft) — min 1, max 100 — Length of the room
- **Room Width** (ft) — min 1, max 100 — Width of the room
- **Room Type** — options: Living Room, Bedroom, Kitchen, Bathroom, Office / Study — Different rooms need different lighting levels

## Outputs

- **Room Area** (sq ft) — Total floor area of the room
- **Recommended Lumens** — Total light output needed for this room
- **Recommended Watts (LED)** — Total LED wattage needed (at ~80 lumens per watt)
- **Bulbs Needed (800 lumen each)** — Number of standard 9W LED / 60W-equivalent bulbs
- **Estimated Annual Cost** — formatted as currency — Yearly electricity cost at $0.13/kWh and 5 hours/day (LED)

## Details

Proper lighting depends on the room's purpose. Kitchens and offices need bright, even light for tasks (70-80 lumens per square foot), while bedrooms need softer ambient light (30-40 lumens per square foot). Living rooms fall in between at 40-50 lumens per square foot, and bathrooms need good task lighting at 60-70 lumens per square foot.

Modern LED bulbs produce about 80 lumens per watt, making them the most efficient choice. A standard 9-watt LED bulb produces approximately 800 lumens, equivalent to a traditional 60-watt incandescent bulb. The calculator divides your total lumen requirement by 800 to determine how many of these standard bulbs you need.

The annual cost estimate assumes LED bulbs used 5 hours per day at the US average electricity rate of $0.13 per kWh. Layered lighting (combining overhead, task, and accent lights) provides the most versatile and attractive illumination.

## Frequently Asked Questions

**Q: What are lumens?**

A: Lumens measure the total amount of visible light emitted by a source. More lumens means brighter light. Watts measure energy consumed, not brightness. A 9W LED and a 60W incandescent both produce about 800 lumens, but the LED uses far less energy.

**Q: How many lumens per square foot do I need?**

A: It depends on the room: kitchens and offices need 70-80 lumens/sq ft, bathrooms 60-70, living rooms 40-50, and bedrooms 30-40. These are general guidelines from the Illuminating Engineering Society.

**Q: Should I use one big light or several smaller ones?**

A: Multiple light sources (layered lighting) provide better, more even illumination. Combine overhead ambient light, task lighting (desk lamps, under-cabinet), and accent lights for the most functional and attractive result.

**Q: What color temperature should I choose?**

A: Warm white (2700-3000K) is best for bedrooms and living rooms. Neutral white (3500-4000K) works well in kitchens and bathrooms. Cool white or daylight (5000-6500K) is ideal for offices and task areas.

**Q: Do dimmer switches save electricity?**

A: Yes, dimming an LED bulb reduces its power consumption roughly proportionally. Dimming to 50% brightness saves about 40-50% of the energy. Make sure your LED bulbs and dimmer switch are compatible (look for 'dimmable' LEDs).

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Source: https://vastcalc.com/calculators/everyday/light-bulb
Category: Everyday Life
Last updated: 2026-04-21