Aquarium calculator: volume, stocking, and dosing in one tool
Updated October 2026
This aquarium calculator runs on the page: tank volume from dimensions, stocking estimates from gallons, and EI dosing scaled to your water change. Type your numbers and every result updates as you go.
Tank volume from dimensions
Measure length, width, and water-line height in centimeters, inside the glass. The tool multiplies them out to liters and US gallons, and you should treat the result as a ceiling, because substrate, wood, and rock displace real volume.
Tank volume, inside dimensions in cm
Length Enter all three dimensions
Stocking and dosing, from your gallons
Tank size Enter your tank gallons
Enter your tank gallons
Video: African Cichlid Hub
The stocking side
The shrimp figure comes from our guide on how many shrimp fit per gallon: start around two to three per gallon and let the colony grow into the space. The betta figure applies the five-gallon minimum for a single betta and divides your gallons by it.
| Number the tool shows | Rule behind it | Covered in depth |
|---|---|---|
| Shrimp count | 2 to 3 shrimp per gallon to start | How many shrimp per gallon guide |
| Betta count | 1 betta per 5 gallons, heated and filtered | Betta tank size guide |
| EI factor and water change | 50 percent weekly change; recipes scale per 10 gallons | EI dosing guide |
Dosing with your real volume
Enter the gallons you actually fill, not the box rating of the tank. The EI factor multiplies any recipe written per ten gallons, and the change figure is half your volume, matching the day-one water change in the EI dosing schedule.
Where the math breaks
Bow-front, corner, and cylindrical tanks cannot use the box formula, since curved glass makes straight-walled math overestimate. Measured outside dimensions also include the glass itself, which on rimless tanks eats a surprising slice of every wall.
Stocking rules here assume small-bodied stock. A heavy-bodied fish carries far more bioload per centimeter than a shrimp, so species-specific planning beats any per-gallon multiplier.
Questions readers ask
How do you calculate gallons from inch measurements?
Multiply length by width by height in inches and divide by 231, the cubic inches in a US gallon. That gives the volume of a rectangular tank at the water line.
Why does my tank hold less than the box rating says?
Substrate, hardscape, filter hardware, and the air gap below the rim all take up space the label never subtracts.
Can I use the stocking numbers for any fish?
No. The shrimp rule is scaled for neocaridina-size bioload, and the betta rule assumes one betta in heated, filtered water. Anything heavy-bodied or territorial needs its own research before you trust a per-gallon multiplier.
