Calculate aquarium capacity accurately to ensure proper fish stocking, medication dosing, and water changes. Therefore, our free tank volume calculator simplifies the process using proven formulas for all shapes.
Aquarium Capacity Calculator
Why Calculate Aquarium Capacity?
Aquarium capacity determines water volume in gallons or liters. Moreover, this guides safe fish numbers—typically 1 inch of fish per gallon. For instance, overstocking leads to poor water quality. Additionally, precise calculations help with salt mix, fertilizer dosing, and pump sizing.
Rectangular Tank Formula (Most Common)
For standard rectangular aquariums, use this simple formula:
Volume (cubic inches) = Length × Width × Height
Convert to gallons: divide by 231 (1 US gallon = 231 cubic inches).
To liters: multiply gallons by 3.785.
Example: 48″ L × 12″ W × 18″ H = 10,368 cu in ÷ 231 = 44.9 gallons (170 liters).
Measure inside dimensions only—subtract glass thickness for accuracy.
Formulas for Other Shapes
Different tanks require specific calculations. Use our calculator for instant results, or apply these:
- Bow Front: Height × Width × Length + 0.5 × r² × (α – sin(α)) × Height
- Cylinder: π × (Diameter/2)² × Height
- Half Cylinder: π × (Diameter/2)² × Height / 2
Pro Tip: Fill to 90% height for safety—never to the brim.
Common Tank Sizes Table
| Dimensions (inches) | Gallons | Liters (approx.) |
| 20 × 10 × 12 | 10 | 38 |
| 36 × 12 × 16 | 29 | 110 |
| 48 × 13 × 20 | 55 | 208 |
| 72 × 18 × 24 | 125 | 473 |
Furthermore, adjust for substrate (subtract 10-15%) and equipment displacement.
Use Our Free Calculator Now
Enter dimensions above for instant results—no downloads needed. Therefore, get gallons, liters, and stocking advice instantly. Perfect for beginners and pros alike.
Calculate your aquarium capacity today and maintain a thriving tank!