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Aquarium Volume Calculator

Calculate fish tank volume, water weight and fish stocking
Last updated: April 2026By the fixnow.tools team — verified seller fee data
Units
Quick Tank Presets
Tank Shape
Tank Dimensions
Length (cm)
Width (cm)
Height (cm)
Fill Level %
Fill level: 90% (typically 85–95%)
Gravel Depth (cm)
Substrate reduces effective water volume
65 L
Aquarium Volume (usable water)
65 L
60 × 30 × 36cm · 64.8L gross · 90% fill
US Gallons
0
usable volume
Water Weight
0kg
water only
Total Weight
0kg
est. with gravel
🐟 Fish Stocking Guide
Small fish (≤5cm) — 1cm per litre0 cm total
Medium fish (5–12cm) — 1cm per 2L0 cm total
Large fish (>12cm) — 1cm per 3L0 cm total
⚠️ These are rough guidelines. Real stocking depends on filtration, plant density, species compatibility and maintenance.

Frequently Asked Questions

How do I calculate aquarium volume? +

Rectangular tank: Length × Width × Height ÷ 1000 (in cm) = litres. Then multiply by your fill percentage and subtract water displaced by gravel.

How many fish per litre? +

A simple rule: 1cm of fish body length per litre for small fish. So a 65L tank can hold roughly 65cm of small fish — about 13 fish at 5cm each. Always consider fish behaviour, territorial needs and filtration capacity.

How heavy is a full aquarium? +

Water weighs 1kg/litre. A 65L tank of water alone = 65kg. Add tank glass (10–20kg), gravel (5–15kg), and equipment. Ensure your stand and floor can support 100–120kg for a medium tank.

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