Aquaponics Fish-to-Plant Ratio Calculator

Aquaponics combines fish farming (aquaculture) with soilless plant growing (hydroponics) in a symbiotic system. Fish waste provides nutrients for plants, and plants filter the water for fish. Getting the fish-to-plant ratio right is essential for a healthy, balanced system.

The Fundamental Ratio: The most widely used guideline is the fish-to-grow-bed ratio: 1 lb of fish per 5–10 gallons of grow bed media or equivalently: 1 kg of fish per 40–80 liters of grow bed media

Fish Stocking Density: Maximum fish density = 1 lb per 5–10 gallons of fish tank water or 1 kg per 40–80 liters

Beginners should start at the lower density (1 lb per 10 gallons) and increase as they gain experience and their biofilter matures.

Feed Rate Ratio (more precise method): Daily fish feed (grams) = Grow bed volume (liters) × 0.5 to 1.0 Plant area (m²) = Daily feed (grams) / 60 to 100

This means for every 60–100 grams of fish food fed daily, you can support approximately 1 square meter (10.8 sq ft) of grow bed.

Common Aquaponics Fish Species:

Plant Capacity by System Size:

Grow bed volume here is 1:1 with the tank, which is the standard media-bed starting point and what the calculator uses. Mature systems often go further, to 1.5:1 or 2:1, because more media means more surface for the nitrifying bacteria and more buffer against a bad week. Going the other way, below 1:1, is where beginners get ammonia spikes.

Best Plants for Aquaponics:

• Easy (low nutrient): Lettuce, herbs (basil, mint), bok choy, Swiss chard, watercress
• Medium: Tomatoes, peppers, cucumbers, beans, peas
• Advanced (high nutrient): Melons, squash, large fruiting plants

Start with leafy greens until your system matures (3–6 months), then graduate to fruiting plants as nutrient levels stabilize.

The Nitrogen Cycle: Fish produce ammonia (NH3) through their gills and waste. Beneficial bacteria (Nitrosomonas) convert ammonia to nitrite (NO2), then other bacteria (Nitrobacter) convert nitrite to nitrate (NO3), which plants absorb as fertilizer.
Establishing that cycle in a new system takes 4 to 6 weeks, and the process is what everyone means when they say “cycling”.

Water Quality Parameters:

System Sizing Rule of Thumb: For a 1:1 ratio system (equal volume fish tank to grow bed), you need approximately 4–8 square feet (0.4–0.75 m²) of growing space per adult fish (tilapia-sized). The calculator works to the middle of that, 6 sq ft per fish.

A family of four can be substantially supplied with fresh produce from a 300-gallon (1,135 L) system. At an experienced stocking density that is 40 to 50 tilapia, which by the rule above wants roughly 250 to 300 sq ft (23 to 28 m²) of growing area. That is a lot of bed for a back garden, and it is the usual reason home builds end up stocked lighter than the tank could carry.

Common Mistakes: Overstocking fish, underfeeding or overfeeding, neglecting to test water, adding fish before the nitrogen cycle is established, and insufficient aeration. Test water at least weekly and maintain a log of readings.