Aquarium Capacity Calculator
Last updated: July 2026 · Free · No sign-up required
Enter values above and click Calculate to see your result instantly.
How the Aquarium Capacity Calculator works
Under the hood, this calculator applies US gallons = (L × W × H in inches) ÷ 231, so the aquarium capacity calculator result you see is genuine math, not a lookup table.
Scroll past the calculator for a quick-reference table, a step-by-step methodology with a fully worked example, and answers to the questions people most often ask about aquarium capacity calculator.
Quick reference
| Tank inches | US gallons |
|---|---|
| 10×10×12 | 5.2 gal |
| 20×10×12 | 10.4 gal |
| 24×12×16 | 20 gal |
| 36×18×18 | 50.5 gal |
| US gal divisor | in³ ÷ 231 |
functions Shows the working, not just the answer
For students and teachers, the final number is only half the value. Every math tool here exposes the formula it applied, the intermediate steps, and the rounding rule, so you can follow along, check your homework, or use the answer in a proof or report with confidence.
calculate Accurate to the spec
Calculations use 64-bit floating point with sensible rounding for the domain (currency to 2 decimals, percentages to 4 decimals, algebra to 6 significant figures). Where exact rational arithmetic matters — fractions, factorials, simplification — we use a dedicated BigNumber path so 1/3 + 1/6 returns ½, not 0.49999.
school Free for classroom use
Educators are welcome to link to any math calculator on CalcaTools from a class site, Google Classroom, or worksheet. The pages are mobile-friendly, free, ad-supported (so we can keep them free) and have no sign-up wall — students just click and use them in class or at home.
tips_and_updates Pair with the spoke articles
Below the calculator we link a small set of plain-English explainer pages — "What is a percentage?", "Why does PEMDAS matter?", and so on. They cover the underlying concept in 4–6 short paragraphs. Read those before the calculator if the topic is new, or after if you want the extra context.
Interpretation guide
| Note | Detail |
|---|---|
| Use inner dimensions | Glass thickness reduces volume |
| Substrate & rock | Displace ~10% of water |
| Fill line below rim | Actual water < full volume |
| Litres | in³ ÷ 61.02 |
Formula & methodology
Formula: US gallons = (L × W × H in inches) ÷ 231
How the result is calculated
A rectangular aquarium’s volume is length times width times height. With inches, dividing the cubic inches by 231 gives US gallons; real water capacity is a bit lower once you account for substrate, décor and the fill line.
- Measure inside length, width and height in inches.
- Multiply them for cubic inches, then divide by 231 for US gallons (or 61.02 for litres).
- Subtract roughly 10% for gravel, rocks and the gap below the rim to estimate true water volume.
Example
A 24 × 12 × 16 inch tank: 24 × 12 × 16 = 4,608 in³ ÷ 231 = 19.9 gallons (about 75 litres).