How do I calculate aquarium volume?

Length x Width x Height in cm, divided by 1000 for liters. A 60x30x40 cm tank = 72 liters. Actual water volume is about 90% due to substrate and decorations.

How many fish can my tank hold?

Conservative rule: 1 inch of fish per gallon (2.5 cm per 3.78 L). A 72-liter tank: about 17 small fish (1.5 inches each). This is a maximum — fewer is healthier.

What size heater do I need?

3-5 watts per liter of water. A 72-liter tank needs a 200-360 watt heater. For rooms that stay warm, use 3W/L. For cold rooms, use 5W/L. We calculate at 3W/L.

What filter flow rate do I need?

The filter should turn over the entire tank volume 4x per hour. A 72-liter tank needs a filter rated at 288 liters/hour (76 GPH). This is the minimum — more is better.

How much substrate do I need?

For 5 cm depth: multiply length x width x 5, divide by 1000, then multiply by 1.6 (gravel density). A 60x30 cm base needs about 14-15 kg of gravel.

How much water do I change weekly?

25% weekly is standard. A 72-liter tank: 16 liters per week. Use a gravel vacuum to remove debris during water changes. Match temperature and treat with dechlorinator.

How do I convert gallons to liters?

1 US gallon = 3.785 liters. 1 liter = 0.264 gallons. A 20-gallon tank = 75.7 liters. A 55-gallon = 208 liters.

Aquarium Calculator - Tank Volume, Fish Capacity & Equipment (2026)

Tank Specifications

Volume, stocking, and equipment

Volume

72 L

Max Fish

Heater

216W

Filter

290 L/h

Common Tank Sizes

Tank	Dimensions (cm)	Volume	Fish Capacity

// Pets · ShashaTools

Aquarium

Length 60 cm

10200

Width (cm)

Height (cm)

Tank Shape

Tank Type

// Results

Volume

72 liters

Volume

72 L (19 gal), ~65 L actual

Fish Capacity

17 small, 5 medium, or 2 large

Heater

216W (3W per liter)

Filter

290 L/hr — 4x turnover

Substrate + Water

9 kg substrate + 16 L weekly change

60x30x40cm: 72L, 17 small fish, 216W heater

How to Use This Calculator

Size your aquarium equipment correctly

Step 1 Enter Dimensions

Measure your tank

Internal dimensions in cm: length, width, height. Measure inside the glass, not outside, for accurate volume.

Select tank shape

Rectangular (standard), bowfront (curved front, ~85% of rectangular volume), or cylinder. Shape affects actual water volume.

Select tank type

Freshwater, planted (needs more light), or saltwater/reef. Type affects lighting requirements. Fish capacity rules are the same.

Read specifications

Volume, fish capacity (small/medium/large), heater watts, filter flow rate, substrate weight, and weekly water change volume.

💡 Volume formula: L × W × H / 1000 = liters. Actual water is ~90% (substrate + decor displace 10%). Always buy equipment for full volume.

Step 2 Stocking Tips

Stock slowly

Add 2-3 fish at a time. Wait 2 weeks between additions. This lets the biological filter (bacteria) adjust to increasing waste load.

Cycle first

Run the tank 4-8 weeks before adding fish (nitrogen cycle). Add ammonia source. Test for 0 ammonia, 0 nitrite. Essential for fish survival.

Understock, not overstock

The fish capacity is a maximum. 70-80% of max is ideal. Fewer fish = better water quality, less disease, less maintenance, happier fish.

Match fish to tank

Active swimmers need long tanks. Bottom dwellers need floor space. Tall tanks suit angelfish. Research species needs before purchasing.

💡 Tip: The #1 beginner mistake is adding fish too soon. An uncycled tank has lethal ammonia levels. Be patient — cycle first, test water, then add fish slowly.

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// Complete Guide — Updated 2026

Aquarium Setup:
The Complete Guide

Setting up an aquarium is one of the most rewarding hobbies, but it requires proper planning. The most common mistakes are overstocking, undersized equipment, and skipping the nitrogen cycle. This guide covers tank sizing, equipment selection, and stocking for success.

Volume Formula

// Tank Volume

Volume (L) = L × W × H (cm) ÷ 1000

60 × 30 × 40 = 72,000 cm³ ÷ 1000 = 72 liters (19 gallons)

Equipment Rules

Equipment	Rule	Example (72 L)
Heater	3W per liter	216 watts
Filter	4x turnover/hr	288 L/hr
Light (planted)	40W per m²	~7 watts
Substrate	5 cm depth	~9 kg
Water change	25% weekly	~16 liters

Real-World Scenarios

Scenario 1: First Tank. James buys a 60x30x40 cm tank (72 liters). Equipment: 200W heater, 300 L/hr filter, 9 kg gravel. He cycles for 6 weeks. Stocks with 6 neon tetras first, waits 2 weeks, adds 4 corydoras, waits 2 weeks, adds a pair of gourami. Total: 12 fish (70% of 17 capacity). Perfect stocking.

Scenario 2: Planted Tank. Maria wants a planted 90x35x45 cm tank (142 L). She needs higher light (planted type) and CO2. Filter: 570 L/hr. Heater: 425W. Plants reduce nitrate naturally, allowing slightly higher stocking. But plants need trimming, fertilizer, and CO2 maintenance.

Scenario 3: Overstocked Disaster. David put 30 fish in his 50-liter tank (capacity: ~12). Within weeks: cloudy water, ammonia spike, fish dying. The filter cannot handle the waste. He rehomes 18 fish, does 50% water changes for a week. Survivors recover. Lesson: capacity is a maximum, not a target.

Scenario 4: Saltwater Reef. Priya plans a 120x45x50 cm reef (270 L). Saltwater needs stronger filtration (protein skimmer), more stable temperature, and lower stocking (50% of freshwater capacity). Budget: 3-5x more than freshwater for the same volume. But the beauty is unmatched.

💡 Key insight: Bigger tanks are actually easier to maintain. A 100-liter tank has more stable water chemistry than a 20-liter. Small tanks are harder for beginners because parameters change rapidly. If this is your first aquarium, go as big as your space and budget allow. Minimum recommended: 50 liters.

Quick Rules

Heater	3W/liter
Filter	4x/hour
Stocking	1"/gallon
Water change	25%/week
Cycle time	4-8 weeks

// Frequently Asked Questions

Common Questions About Aquariums

How to calculate tank volume? +

L x W x H (cm) / 1000 = liters. 60x30x40 = 72 L. Actual water ~90% (substrate/decor). Divide liters by 3.785 for gallons.

How many fish in my tank? +

1 inch of fish per gallon (2.5cm/3.78L). 72L tank: ~17 small fish. This is maximum — stock to 70-80% for healthier fish.

What heater size? +

3-5 watts per liter. 72L = 216-360W. Warm rooms: 3W/L. Cold rooms: 5W/L. Two smaller heaters better than one large.

What filter flow rate? +

4x tank volume per hour minimum. 72L = 288 L/hr filter. More is better. Canister filters are quietest and most effective.

How much substrate? +

5 cm depth: L x W x 5 / 1000 x 1.6 kg/L. 60x30 base = ~14 kg gravel. Planted tanks may need nutrient-rich substrate.

How much water to change weekly? +

25% weekly. 72L tank = 16 liters. Use gravel vacuum. Match temp. Treat with dechlorinator. Consistent schedule is key.

What is the 1-inch-per-gallon rule? +

Rough stocking guide: 1 inch adult fish per gallon. Works for small slim fish. Not for large/messy/deep-bodied species.

Gallons to liters? +

1 US gallon = 3.785 liters. 20 gal = 75.7 L. 55 gal = 208 L. Use our Unit Converter for exact conversions.

Do I need a heater? +

For tropical fish: yes. They need 24-28°C. Room temp fluctuations stress fish. Even warm climates have nighttime drops.

What is the nitrogen cycle? +

Bacteria convert ammonia → nitrite → nitrate. Takes 4-8 weeks. Must complete before adding fish. Skipping = dead fish.

AquariumCalculator

Aquarium Setup:The Complete Guide

Volume Formula

Equipment Rules

Real-World Scenarios

Aquarium
Calculator

Aquarium Setup:
The Complete Guide