Tank Size, Weight, and Gravel Calculators for Fishkeepers

Not sure how many gallons your fish tank is?

Wondering just how heavy your full fish tank will be?

Need to buy substrate for your aquarium but not sure just how much to buy?

These are important calculations that will both help keep your aquarium healthy AND save you money.

Choose a calculator below, enter the numbers, and the results will automatically be populated!

Fish Tank Size Calculator

Now that you know how big your tank is, it’s time to choose the fish!

Here are three guides to give you an idea of where to start:

  1. A List of the Best Freshwater Aquarium Fish for Beginners
  2. A List of the Best Saltwater Aquarium Fish for Beginners
  3. The 14 Most Colorful and Beautiful Aquarium Fish

How To Calculate Fish Tank Size

If you’re interested in the details behind the tank size calculator above, the equation is very simple.

If you measure in inches, here’s the formula:

  • (L*W*H)*0.0043290 = Gallons

If you measure in centimeters, here’s the formula:

  • (L*W*H)*0.00026417 = Gallons

Basically, you’re calculating cubic inches or cubic centimeters, first.

Then, you’re doing a conversion between cubic inches/centimeters and gallons.

Note that we’re using US Gallons in these equations.


Fish Tank Weight Calculator

Now that you know how heavy your aquarium will be when full, you can make the right choice when it comes to deciding where it goes and what kind of stand you need.

How To Calculate Fish Tank Weight

First, calculate the volume of your tank, using our calculator above. Then, multiply that number by 8.345 pounds for freshwater aquariums or 8.554 for saltwater tanks.

  • Gallons*8.345 = Weight of water in freshwater aquariums (in pounds)
  • Gallons*8.554 = Weight of water in saltwater aquariums (in pounds)

You’ll also want to know how heavy your aquarium is without water in it. Here are some rough estimations for glass tanks:

  • 5 gallons: 5-8 pounds
  • 10 gallons: 10-13 pounds
  • 20 gallons: 23-27 pounds
  • 40 gallons: 52-58 pounds
  • 75 gallons: 100-150 pounds
  • 150 gallons: 300-350 pounds

Substrate Quantity Calculator

For a standard, fish-only tank, you’re probably looking at around 2 inches of gravel or sand.

However, if you want a planted tank (which we recommend in most cases), you’ll want to factor in an additional 1 inch of nutrient layer below the sand or gravel.

Therefore, if you have a planted tank, use the calculator twice. Once for sand or gravel, and then once again for a base substrate (use the value in the wet sand column as a rough guide for nutrient substrate).

Further reading:

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