Tanks & LiquidsV_net = (L - 2t) × (W - 2t) × (Water Height - Substrate) / 231

Aquarium Volume & Water Weight Calculator

Compute net water volume and filled tank weight for rectangular, bowfront, cylinder, and hex fish tanks with substrate volume displacement.

Aquarium Volume & Net Water Solver

Gross vs net water • Total weight • Filter & heater sizing

Presets:

1. Tank Shape & Dimensionsrectangular or circular

Aquarium Shape

Length (L)

Width (W)

Height (H)

2. Water Level & Substratenet displacement

Top Water Gap

Substrate Bed Depth

3. Actual Water VolumeNet Space

Net Water Volume

Gross External Tank Volume54.08 US gal (204.7 L)

4. Total Weight & Equipment

Total Filled Tank Weight (Glass + Water + Sand)515 lbs (233 kg)

Recommended Filter Flow Rate (4-6× turnover)200 - 300 GPH

Recommended Aquarium Heater200 - 250 Watts

Formulas, calculation steps & FAQs below↓

Formulas & Calculation Guide

Sizing Aquariums & Net Water Volume

A common mistake in fishkeeping is dosing medications or stocking fish based on the exterior glass dimensions printed on the retail box. A nominal “55-gallon” aquarium rarely holds more than 44 to 47 gallons of actual water.

Calculation Breakdown

Exterior Gross Volume (US Gallons):
- Rectangular Tank: Gross Gallons = (Length_in × Width_in × Height_in) / 231
- Circular / Cylinder Tank: Gross Gallons = (π × (Diameter_in / 2)² × Height_in) / 231
Net Water Volume (Accounting for Substrate & Rim Gap):
- Net Water Height = Height_tank - Rim_Air_Gap - Substrate_Depth
- Rectangular: Net Gallons = (Length_in × Width_in × Net Water Height) / 231
- Circular: Net Gallons = (π × (Diameter_in / 2)² × Net Water Height) / 231
Structural Load / Total Filled Weight:
- Water Weight = Net Gallons × 8.344 lbs
- Substrate Weight ≈ Substrate Gallons × 12.5 lbs
- Total Floor Load = Water + Substrate + Glass/Acrylic Tank + Cabinet Stand

Aquarium setup – calculation example

Let’s size a standard 55-gallon tank (48” × 13” × 21”):

Enter tank dimensions: length = 48 in, width = 13 in, height = 21 in.
Enter the water line gap: rim gap = 1.5 in.
Enter the gravel depth: substrate = 2 in.
The calculation results are available for you: gross volume = 56.7 gal, net water volume = 44.8 gal, and total filled weight = 525 lbs.

💡 Standard aquarium glass weighs roughly 10–12 lbs per gallon when filled. Ensure your flooring joists can support this static load.

Standard Aquarium Dimensions Cheat Sheet

Nominal Tank Size	Outside Dimensions (L × W × H / Dia × H)	Empty Weight	Total Filled Weight
10 Gallon Leader	20” × 10” × 12” (Rectangular)	11 lbs	~111 lbs (50 kg)
15 Gallon Cylinder	18” Dia × 16” H (Circular)	18 lbs	~150 lbs (68 kg)
20 Gallon Long	30” × 12” × 12” (Rectangular)	25 lbs	~225 lbs (102 kg)
29 Gallon	30” × 12” × 18” (Rectangular)	40 lbs	~330 lbs (150 kg)
30 Gallon Column	20” Dia × 24” H (Circular)	35 lbs	~320 lbs (145 kg)
55 Gallon	48” × 13” × 21” (Rectangular)	78 lbs	~625 lbs (283 kg)
75 Gallon	48” × 18” × 21” (Rectangular)	140 lbs	~850 lbs (385 kg)
125 Gallon	72” × 18” × 21” (Rectangular)	206 lbs	~1,400 lbs (635 kg)

Frequently Asked Questions

Expert answers to common calculations, unit conversions, and dimensional requirements.

What is the difference between gross aquarium volume and net water volume?↓

Gross volume is the exterior boundary of the glass tank (Length × Width × Height / 231). Net volume is the actual water contained after subtracting the thickness of the glass panels, the 1-to-2 inch empty air gap between the water line and the rim, and the physical volume displaced by gravel, sand substrate, driftwood, and rocks (typically 10% to 15% less than gross volume).

How much does a filled aquarium weigh per gallon?↓

Freshwater weighs 8.34 pounds per US gallon (1.0 kg per liter), and saltwater weighs approximately 8.55 pounds per gallon. Once you add the weight of the glass tank itself, heavy gravel or sand, and equipment, a reliable rule of thumb is 10 to 12 pounds per gallon of total tank capacity.

What filter flow rate (GPH) do I need for my aquarium?↓

For freshwater community tanks, target a filter turnover rate of 4 to 5 times the tank volume per hour (e.g., a 30-gallon tank needs 120–150 GPH). For heavily stocked cichlid aquariums, goldfish tanks, or marine reef aquariums, target 8 to 10 times turnover per hour (240–300 GPH).

How many watts of aquarium heater do I need?↓

The standard rule is 3 to 5 Watts per gallon of water to maintain a temperature 5°F to 10°F above ambient room temperature. For example, a 50-gallon tank requires a 150W to 250W heater.