🐠 Aquarium Size Calculator
Calculate volume, weight, and stocking capacity
📏 How to Measure Your Tank
For the most accurate volume calculation, measure the internal dimensions of your tank. If you measure the outside, subtract the glass thickness (usually 1/4" to 1/2") from each measurement.
Common Standard Sizes
- 10 Gallon: 20" L x 10" W x 12" H
- 20 Gallon Long: 30" L x 12" W x 12" H
- 29 Gallon: 30" L x 12" W x 18" H
- 55 Gallon: 48" L x 13" W x 21" H
- 75 Gallon: 48" L x 18" W x 21" H
"Don't forget about displacement! A '55-gallon' tank rarely holds 55 gallons of water. Once you add 50 lbs of gravel, 30 lbs of rock, and leave an inch of space at the top, you might only have 40-45 gallons of actual water. This matters when you're dosing medication—always dose for the actual water volume, not the tank size, to avoid overdosing."
🐟 Stocking Guidelines
The "1 inch per gallon" rule is a popular but simplified guideline. It works okay for small, slim fish like Neon Tetras, but fails for larger fish.
Better Stocking Rules:
- Surface Area Rule: Fish need oxygen exchange at the surface. A wide, shallow tank supports more fish than a tall, narrow one of the same volume.
- The "Adult Size" Rule: Always calculate based on the fish's adult size, not the size they are at the store. That 1-inch Oscar will grow to 12 inches!
- Filtration Matters: A tank with a powerful canister filter can support a slightly higher bioload than one with a simple sponge filter.
⚠️ Common Mistakes
1. Overstocking immediately: New tanks need to "cycle" (build beneficial bacteria). Add only 1-2 hardy fish at first, then wait a few weeks.
2. Ignoring weight: Water is heavy (8.34 lbs/gal). A 55-gallon tank weighs over 600 lbs filled. Make sure your floor and stand can handle it.
3. Not accounting for substrate: If you want a deep sand bed (4+ inches), you lose significant water volume.
Alex Chen, Calcs.top
Professional Aquarist, 12 years experience