Aquarium Lighting Calculator
Plants and corals live on light. Tell us your tank size and setup type — we'll recommend the right LED wattage.
Calculate lighting wattage
How lighting sizing works
Modern LED aquarium lights are usually sized by watts per gallon, a rule of thumb carried over from the fluorescent era that still works well as a starting point:
- 0.3–0.6 W per gallon — fish-only tanks, light is just for viewing
- 1–1.5 W per gallon — low-tech planted tanks (easy plants, no CO₂)
- 2–3 W per gallon — high-tech planted tanks (CO₂ + fertilizers)
- 3–4.5 W per gallon — reef tanks with corals
These ranges assume full-spectrum LED fixtures. Deeper tanks need more punch to reach the bottom, so if your tank is over 18 inches tall, aim for the upper end of your range.
Lighting tips
- Start with a 6–8 hour photoperiod and only extend it once plants are clearly thriving.
- More light without matching CO₂ and nutrients grows algae, not plants — balance the three.
- A dimmable fixture or riser legs lets you dial intensity down instead of buying a new light.
- Put the light on a timer — consistent day length beats a longer, irregular one.
Frequently asked questions
How many watts do I need for a 20 gallon planted tank?
20–30W of LED for a low-tech setup, or 40–60W if you run CO₂ and want fast, demanding plant growth.
Is more light always better for plants?
No. Light is only one leg of the triangle — plants also need CO₂ and nutrients. Extra light without the other two just feeds algae.
LED vs fluorescent for aquariums?
LED wins on almost every count: more efficient, dimmable, no yearly bulb replacements, and better color control for reefs.
How long should aquarium lights be on per day?
6–8 hours for planted tanks, 8–10 for fish-only. Keep it consistent with a timer.