Aquarium Measurement Charts: Choosing the Right Aquarium Size

Selecting the perfect aquarium for your home or office can be exciting yet challenging. With so many shapes, sizes, and styles, how do you know which is right for your needs? Properly measuring and calculating aquarium dimensions is key to finding the ideal tank size and avoiding issues. This comprehensive guide breaks down everything you need to know about aquarium sizes, from why it matters to how to measure, standard dimensions, size calculators, cost considerations, units of measurement, and frequently asked questions. With the help of detailed measurement charts and expert insights, you can select the perfect aquarium confidently. So, let’s dive right in!

Why Aquarium Size Matters

Aquarium size is much more than just aesthetics. Choosing the right tank volume for your setup has important implications for your fish’s and aquatic life’s health and well-being. Here’s an overview of why aquarium dimensions do matter:

  • Prevents Overcrowding – Fish need adequate swimming space to thrive. An overcrowded tank increases stress, aggression, poor water quality, disease transmission, and stunted growth. Adhering to gallon-per-inch rules prevents overstocking.
  • Dilutes Waste Buildup – More water volume dilutes metabolites like ammonia and nitrates, keeping levels in check between water changes. Small tanks are prone to dangerous chemical spikes.
  • Options for Aquascaping – Bigger tanks allow you to get more creative with hardscapes, plants, décor, and substrates. More real estate to work with can lead to more stunning aquascape designs.
  • Temperature Stability – Large water volumes resist fluctuations in temperature, keeping things stable for inhabitants. Sudden temperature swings can shock or kill fish.
  • Easier Maintenance – Larger aquariums require fewer water changes compared to smaller tanks. There’s more wiggle room between water parameter spikes. Less frequent maintenance is easier on you and your fish.

The takeaway? While a larger aquarium may cost more upfront, the long-term benefits for your fish make it well worth the investment. When in doubt, always opt for bigger rather than smaller.

How to Estimate the Size of Your Aquarium

If you’re purchasing a new tank, double checking used tank dimensions, or want to estimate an existing aquarium’s volume, knowing a few simple measurement techniques can be invaluable:

  • Inside vs Outside Dimensions – Most aquariums have significant glass thickness unlike a fish bowl. Always measure inside tank dimensions length x width x height for the most accurate volume estimate.
  • Use a Tape Measure – A simple metric or imperial measuring tape allows you to measure tank sides in inches or centimeters easily. Measure from the exact inner edges of each glass panel.
  • Fill with Known Quantities – Gradually filling with known volumes like gallon milk jugs can gauge overall size for odd shaped tanks. Mark fill levels and tally the amounts used.
  • Utilize Volume Calculators – Numerous aquarium volume calculators exist online. Input your interior L x W x H measurements to get estimated tank capacity.
  • Read Manufacturer Specs – For new purchases, check the listed dimensions and volume the manufacturer provides for exact tank capacity before buying.

Following these tips will ensure you know the true interior size and resulting water volume before making any decisions. Never rely solely on vague labels like “20 gallon” or outside measurements.

Standard Aquarium Sizes

While each brand varies slightly, most traditional rectangular aquariums adhere to general interior dimension standards correlated with their gallon capacity. Here are the typical lengths, widths, and heights for common aquarium sizes:

  • 10 Gallon Tank – 20 x 10 x 12 inches (50 x 25 x 30 cm)
  • 20 Gallon Tank – 24 x 12 x 16 inches (60 x 30 x 40 cm)
  • 29 Gallon Tank – 30 x 12 x 18 inches (75 x 30 x 45 cm)
  • 40 Gallon Breeder Tank – 36 x 18 x 16 inches (90 x 45 x 40 cm)
  • 55 Gallon Tank – 48 x 13 x 21 inches (120 x 33 x 53 cm)
  • 75 Gallon Tank – 48 x 18 x 21 inches (120 x 45 x 53 cm)
  • 90 Gallon Tank – 48 x 18 x 24 inches (120 x 45 x 60 cm)
  • 120 Gallon Tank – 48 x 24 x 24 inches (120 x 60 x 60 cm)
  • 150 Gallon Tank – 60 x 18 x 28 inches (150 x 45 x 70 cm)
  • 180 Gallon Tank – 72 x 18 x 25 inches (180 x 45 x 63 cm)

Keep in mind rimless tanks subtract 1⁄2 to 1 inch from the dimensions. And long tanks value length over height. As you can see, each incremental size increase offers significantly more swimming space!

Aquarium Size Calculators

Rather than memorizing standard tank dimensions, one shortcut is to turn to an online aquarium capacity calculator. These handy web-based tools allow you to input your interior aquarium measurements in inches or centimeters and instantly determine the estimated gallon or liter volume.

Most calculators follow a basic formula:

  • Gallons = (Length in inches x Width in inches x Height in inches) / 231
  • Liters = (Length in cm x Width in cm x Height in cm) / 1000

So for example, inputting a tank measuring 36” Long x 18” Wide x 24” High would calculate:

(36 x 18 x 24) / 231 = 75.4 gallons

These calculators provide quick, reliable volume estimates without any math on your part. Just be sure to use precise interior tank measurements. Common calculators include:

  • Aquarium Volume Calculator by Inch Calculator
  • Aquarium Capacity Calculator by
  • Aquarium Size Calculator by Allpondsolutions

Having access to these tools makes determining tank sizes a breeze. Just input dimensions and instantly get the volume for any regular, corner, bowfront or oddly-shaped tank.

Aquarium Size and Price Comparison

One major factor to weigh when deciding on aquarium size is how it affects the overall setup cost. As a general rule of thumb:

  • Small aquariums under 29 gallons offer the most affordable options.
  • Midsize tanks from 40 to 75 gallons have moderate prices.
  • Large aquariums over 90 gallons come with a premium price tag.

But larger aquariums may provide more value over time, considering:

  • Bigger tanks allow for more fish, corals, plants or invertebrates. Spreading out costs across more livestock.
  • Large volumes dilute expenses like electricity, filtration, heaters. Items can be lower wattage/capacity.
  • Maintenance costs are lower over time. Fewer water changes, equipment replacements needed.

Here’s a breakdown of how aquarium size typically correlates to price:

Aquarium SizeTypical Price Range
10 Gallon$50 – $100
20 Gallon$100 – $250
40 Gallon$200 – $400
60 Gallon$300 – $600
90 Gallon$500 – $1000
120 Gallon$800 – $1500
150+ Gallons$1200+

While bigger tanks have a larger upfront investment, mature aquarists agree their long-term value outweighs initial setup costs.

Understanding Aquarium Measurements

With aquariums sized in both imperial and metric units, it’s helpful to understand conversions between inches, feet, centimeters, and meters to interpret dimensions best:

  • 1 inch = 2.54 centimeters
  • 1 foot = 12 inches = 30.48 centimeters
  • 1 meter = 100 centimeters = 39.37 inches
  • 1 gallon = 3.785 liters

Common measurements like tank lengths can be converted as follows:

  • 24 inches = 61 centimeters
  • 36 inches = 91.4 centimeters
  • 48 inches = 121.9 centimeters
  • 4 feet = 121.9 centimeters

Knowing these unit conversions lets you quickly compare aquarium sizes across any measuring system. While imperial units like gallons and inches are often used for tank volumes and dimensions in the aquarium hobby, being well-versed in metric units can be beneficial when researching international products or communicating with metric-based countries.

Frequently Asked Questions

What are the standard fish tank sizes?

The most common fish tank sizes are 10, 20, 29, 40, 55, 75, and 90 gallons. Tanks in this range offer versatile freshwater and saltwater setup options. Larger tanks of 120, 150, 180+ gallons are less widespread but allow advanced reef systems.

How do you measure the size of a fish tank?

Use a tape measure to measure the tank’s inner length, width, and height in inches or centimeters. Input these dimensions into an online aquarium capacity calculator to estimate the total gallon or liter volume. Only use interior tank measurements for accuracy.

How many gallons is a 24 x 12 x 12-inch tank?

A tank with interior dimensions of 24 x 12 x 12 inches equates to 24 x 12 x 12 = 3456 cubic inches

3456 cubic inches / 231 cubic inches per gallon = 15 gallons

So, a tank measuring 24 inches long x 12 inches wide x 12 inches tall contains approximately 15 gallons.


Selecting the perfect aquarium for your needs requires careful consideration of size and dimensions. Armed with this knowledge, you can confidently shop for your new tank. Refer to the detailed measurement charts and size comparisons as a guideline.

And don’t forget to double-check manufacturer-stated volumes against your interior measurements. Investing in the largest reasonably-sized aquarium your space allows provides the healthiest, most stable environment for your aquatic life to thrive.