Aquarium Volume Calculator β Tank Size, Heater, Filter & Weight
An all-in-one aquarium calculator that computes tank volume in US/UK gallons and liters, water weight (critical for stand and floor load), recommended heater wattage, filter flow (GPH) and substrate weight. Supports six tank shapes β rectangular, cylindrical, hexagonal, bow-front, corner-pentagon and corner-quarter-cylinder. Verify floor load against the USDA floor-load guidance for residential structures before placing tanks over 75 gal on upper floors.
Calculator
Aquarium volume terms β quick reference
- Displacement volume
- The true water volume of a filled tank, accounting for glass thickness, substrate and rocks β usually 85-95% of advertised size.
- US vs UK gallon
- 1 US gallon = 3.785 L; 1 UK (imperial) gallon = 4.546 L. A 20 UK-gal tank holds 24 US gal.
- Filter GPH (gallons per hour)
- Filter flow rating. Aim for 4-10Γ tank volume per hour for community freshwater stocks.
- Substrate depth
- Recommended 1.5-2 inches for non-planted tanks, 2.5-3 inches for planted tanks rooted-plant species.
Common aquarium sizes
| Name | Dimensions (LΓWΓH) | Volume | Water weight |
|---|---|---|---|
| 10-gal standard | 20 Γ 10 Γ 12 in | 10 gal | 83 lb |
| 20-gal high | 24 Γ 12 Γ 16 in | 20 gal | 167 lb |
| 20-gal long | 30 Γ 12 Γ 12 in | 20 gal | 167 lb |
| 29-gal | 30 Γ 12 Γ 18 in | 29 gal | 242 lb |
| 55-gal | 48 Γ 13 Γ 21 in | 55 gal | 459 lb |
| 75-gal | 48 Γ 18 Γ 21 in | 75 gal | 626 lb |
| 125-gal | 72 Γ 18 Γ 21 in | 125 gal | 1 043 lb |
Frequently Asked Questions
How do I calculate aquarium volume?
Rectangular: length Γ width Γ height in inches, divided by 231 to get US gallons. Cylindrical: Ο Γ radiusΒ² Γ height Γ· 231. The calculator handles 6 common shapes (rectangular, cylindrical, hexagonal, bow-front, corner-pentagon, corner-quarter-cylinder).
How heavy is a full aquarium?
Water alone weighs 8.345 lb per US gallon. A 55-gallon tank holds ~459 lb of water, plus ~25 lb of glass and ~90 lb of substrate β roughly 575 lb total. Always verify your floor and stand can support it.
What wattage heater do I need for my tank?
The rule of thumb is 3β5 watts per US gallon. A 30-gallon tank needs 90β150 W; a 55-gallon tank needs 165β275 W. Use higher wattage in cold rooms or unheated basements.
What filter flow rate is ideal?
Aim for 4β10Γ tank volume per hour. A 30-gallon tank needs 120β300 GPH. Planted, low-bioload tanks can use the low end; high-bioload tanks (cichlids, goldfish) need the high end.
How much gravel do I need for my tank?
A 2-inch gravel bed requires about 1 lb per gallon per inch β so roughly 2 lb/gal. A 30-gallon tank needs ~60 lb of standard aquarium gravel. Planted substrates are lighter (~60 lb/ftΒ³ vs 100 lb/ftΒ³ for gravel).
Why is my calculated volume different from the advertised tank size?
Advertised size usually rounds up and includes a few inches of glass and rim. Actual usable water volume is 85β95 % of advertised. Our calculator gives the inside-glass volume based on dimensions you enter.
Can I use metric dimensions?
Yes β the calculator accepts inches or centimeters. Convert 1 inch = 2.54 cm. Output is given in US gallons, UK gallons and liters.
What's the difference between US and UK gallons?
US gallon = 3.785 L; UK (imperial) gallon = 4.546 L. Always check which unit a fish-stocking guide uses β a 20 UK gallon tank is actually 24 US gallons.
Sources & References
- [1]Aquarium Glass and Tank Size Reference β Aquarium Co-Op
- [2]Heater sizing for freshwater and saltwater aquariums β Petco Pet Care
- [3]Fishkeeping World β Tank Size Calculator Guide β Fishkeeping World
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