How to Calculate Aquarium Volume in Gallons & Liters
Calculating exact aquarium water capacity is essential for dosing water conditioners, sizing canister or hang-on-back filters, and choosing proper heater wattage. The fundamental conversion constant for liquid US gallons is 231 cubic inches per US liquid gallon.
Rectangular Tank Formula
Gallons = (L × W × H) ÷ 231
Multiply length, width, and height in inches, then divide by 231 cubic inches.
Cylinder Tank Formula
Gallons = (π × Radius² × H) ÷ 231
Multiply Pi (3.14159) by squared radius and height in inches, then divide by 231.
Standard Fish Tank Dimensions & Filled Weight Chart
| Standard Size | Dimensions (L × W × H) | Empty Weight | Filled Weight (Water + Gravel) |
|---|---|---|---|
| 10 Gallon Standard | 20" × 10" × 12" | 11 lbs | 111 lbs (50 kg) |
| 20 Gallon Long | 30" × 12" × 12" | 25 lbs | 225 lbs (102 kg) |
| 29 Gallon Standard | 30" × 12" × 18" | 40 lbs | 330 lbs (150 kg) |
| 40 Gallon Breeder | 36" × 18" × 16" | 58 lbs | 458 lbs (208 kg) |
| 55 Gallon Standard | 48" × 13" × 21" | 78 lbs | 624 lbs (283 kg) |
| 75 Gallon Heavy | 48" × 18" × 21" | 140 lbs | 850 lbs (386 kg) |
Frequently Asked Questions
How do I calculate the volume of a rectangular fish tank in US gallons?
To calculate the volume of a rectangular aquarium in US gallons, multiply length by width by height in inches (L x W x H), then divide the total cubic inches by 231. For example, a 30" x 12" x 12" tank equals 4,320 cubic inches / 231 = 18.7 US Gallons.
How much does a filled 55-gallon fish tank weigh?
A 55-gallon freshwater aquarium filled with water weighs approximately 458 lbs (208 kg) for the water alone. When including the glass tank frame, gravel substrate, and rocks, the total filled weight reaches 600 to 650 lbs (272 to 295 kg).
How much gravel or sand substrate do I need for my aquarium?
A general rule of thumb is 1.5 to 2 pounds of gravel per gallon of water, or approximately 0.08 pounds of substrate per square inch of bottom surface area to achieve a standard 2-inch (5 cm) deep substrate bed.
Can my wooden floor or second-floor room hold a 75-gallon aquarium?
A filled 75-gallon tank weighs around 850 to 900 lbs. Placing a tank of this weight parallel across multiple floor joists against a load-bearing wall is safe, but tanks over 100 gallons placed in the middle of a room may require floor joist reinforcement.
What size filter (GPH) and heater (Watts) do I need for my tank?
Choose an aquarium filter with a turnover rate of at least 5 times your tank volume per hour (e.g. a 20-gallon tank requires a 100 GPH filter). For heating, use 5 Watts per gallon of water in standard room temperatures.
What is the 1 inch of fish per gallon stocking rule?
The 1 inch of slender fish per 1 to 1.2 gallons rule applies to small community fish like neon tetras. Deep-bodied fish like goldfish or cichlids create much higher bio-loads and require 1 inch of fish per 2 to 3 gallons.