Aquarium Light Calculator
What is the Aquarium Light Calculator?
This calculator suggests the right light level for your tank size. We give you a PAR range (what plants and corals actually use) and a watts-per-gallon range for LED fixtures.
Choose low, medium, or high light based on your plants or reef goals. Tank depth matters—deeper tanks need more powerful lights to reach the substrate.
How to Use This Calculator
- Enter your tank dimensions or volume.
- Select your goal: low, medium, or high light (planted or reef).
- Use the PAR and wattage ranges when shopping for LED or other lights.
- Run lights 6–10 hours per day on a timer for consistency.
How would you like to enter your tank info?
Tank dimensions
What's your tank shape?
Enter Your Tank Dimensions
Light level
Refinements
Salt and tannins absorb more light; effective PAR at depth is lower than in clear freshwater.
Pendants give higher center PAR but less even coverage; strips spread more evenly.
Need Help Measuring Your Tank?
How to Measure Your Aquarium →
Not sure how to measure your tank dimensions? We have a complete visual guide with step by step instructions.
Click to see the full measuring guide
What's Next?
Complete your aquarium setup with these helpful calculators:
What is the Aquarium Light Calculator?
This calculator suggests the right light level for your tank size. We give you a PAR range (what plants and corals actually use) and a watts-per-gallon range for LED fixtures.
Choose low, medium, or high light based on your plants or reef goals. Tank depth matters—deeper tanks need more powerful lights to reach the substrate.
How to Use This Calculator
- Enter your tank dimensions or volume.
- Select your goal: low, medium, or high light (planted or reef).
- Use the PAR and wattage ranges when shopping for LED or other lights.
- Run lights 6–10 hours per day on a timer for consistency.
Aquarium Lighting: PAR, Lumens, and What Actually Grows Plants
Aquarium lighting has moved from watts and lumens to PAR—Photosynthetically Active Radiation. PAR measures the light that plants and corals use for photosynthesis (roughly 400–700 nm). So when we say “30 PAR at the substrate,” we mean 30 µmol/m²/s of useful light reaching the bottom of the tank.
Why Watts Per Gallon Is Outdated
The old “watts per gallon” rule was for T12 fluorescents. High-efficiency LEDs (e.g. Radion, Kessil) need far fewer watts: roughly 0.25–0.5 W/gal for low light, 0.5–0.75 for medium, 0.75–1.25 for high. Budget LEDs need more total watts for the same PAR. Overdriving wattage on premium fixtures can bleach corals or cause algae—PAR is what you should compare when buying.
Depth, Water Type, and Mounting Height
Tank depth matters most: a 24-inch-deep tank needs more power than a 12-inch one for the same PAR at the substrate. Water type matters too: saltwater and blackwater absorb more light (~0.9× and ~0.7× effective PAR vs clear freshwater). Mounting height: lights 8" or more above the water lose significant PAR at the bottom. Strip LEDs give even spread; pendants give higher center PAR but less coverage.
Photoperiod and Consistency
Most aquariums do best with 6–10 hours of light per day. Use a timer so the schedule is consistent. Ramping up and down (dimmer or sunrise/sunset) can reduce stress and algae. Start at the lower end of the recommended range and increase only if plants or corals need more.