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How Much Gravel Do I Need For My Aquarium? Facts & FAQs

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By Lindsey Stanton

aquarium with plants and gravel

The substrate in your aquarium is much more important than you might think. The substrate is that layer at the bottom of the tank which can be sand, some kind of aquarium soil, rocks, or usually gravel. Putting together a nice aquarium is not all that difficult, but there are some tricky aspects and points of interest that you need to know about.

One of these conundrums is deciding exactly how much gravel should be in your aquarium. So, how much gravel do I need for my aquarium? First, let’s talk about some important factors that you need to think about.

tropical fish 2 divider Factors to Think About

When it comes to deciding the type of gravel you need for an aquarium, as well as the amount of it, there are a few different things that you should keep in mind. Let’s go over the different factors that will work towards deciding what kind of gravel and how much of it you are going to put in your tank. If you do need some good substrate suggestions then check out this article.

Image Credit: Mirek Kijewski, Shutterstock


Your fish are going to help you decide what kind of gravel you need and how much of it. Some fish prefer really coarse gravel which they can mess around in and others prefer finer gravel which they can dig around and forage in. To determine the type and amount of gravel you use, you should first figure out what fish are going to be in the aquarium and what their preferences are.


Another big determining factor here is what kind of plants you want to have in your aquarium. Plants that do not have any root systems could care less about the amount and type of gravel because they get their nutrients from the water. However, rooted plants are definitely going to care.

Really big rooted plants are going to require finer gravel and they will need a deeper layer of it. This is because large plants will be top-heavy and they need a lot of nutrients, which means that they need a fairly thick and compact layer of gravel. Smaller plants with smaller root systems can do with coarser gravel and a shallower layer of it.

fish-tank gravel
Image Credit: Jeon Sang-O from Pixabay

Size & Decorations

Of course, the size of your aquarium is going to determine how much gravel you need to have at the bottom of the tank. On a side note, the type of decorations you have present in the tank will also determine how much gravel you need.

From an aesthetic viewpoint, if you have lots of large decorations, more gravel will look better. Also, if you have decorations that need to be anchored down, they will require a fair amount of gravel. (you can also get cool different colored gravel, we have covered our top 5 here).

So, How Much Gravel Do I Need for My Aquarium?

Once you have taken all of the above considerations into account, calculating how much gravel you will need for your aquarium is pretty straightforward. A good place to start is with 2 inches of gravel as a substrate for any freshwater aquarium. 2 inches is what most people would consider to be the minimum.

You need to use the tank’s dimensions and size to determine the exact amount. For example, a tank of 55 gallons that is 49 by 12 inches will need around 30 pounds of gravel for a 1-inch bed. After you have figured this out, you can then multiply the depth in inches by the amount of gravel you calculated for 1 inch.

For example, the above calculation would require 60 pounds of gravel for a 2-inch bed in that same aquarium.

fish in tank gravel
Image Credit: Pixabay

Aquarium Gravel Calculator

Your best bet is to use a gravel calculator online like this one.

fish divider FAQs

How Much Gravel for a 5-Gallon Tank?

Generally speaking, around 1 pound of substrate per gallon of water is what you want to go for. So, for a 5-gallon tank, this means you should be using about 5 pounds of gravel substrate.

If you are unsure of exactly how much gravel you need, using a simple fish tank gravel calculator will do the trick.

How Much Gravel Do I Need for a 20-Gallon Fish Tank?

Based on our previous requirement of 1 pound of gravel per gallon of water, this means that you will need roughly 20 pounds of gravel substrate for a 20-gallon fish tank.

What Can I Use Instead of Gravel In My Fish Tank?

Instead of gravel, some people choose to use much finer aquarium rocks, more smooth pebbles than anything else. Sand is also another good option to go with, especially for marine environments.

If you have a heavily planted tank or want to make one, and are not too concerned about cleanup time, aquarium soil is another option you can go with. Some people do not use substrate at all, although this is not recommended.

powered gravel cleaner in aquarium
Image Credit: Dmitri Ma, Shutterstock

Can You Put Gravel In Fish Tank After Water?

Technically sure, you can put gravel in a fish tank after water, but it’s just going to make much more of a mess than if you put it in first.

Some gravel can be a bit floaty, and getting it to the right position can be hard, plus it will really loosen up all of the debris on it if you do it this way.

By all means, it’s much easier to put the gravel in the tank before you add the water.

How Often Should You Change Gravel In Fish Tank?

If you get high-quality gravel, you vacuum it often, and you wash it every now and then too, you really should never have to replace the gravel in your aquarium.

Some cheaper options may begin to break down after a year or so, but this should not be a problem if you purchase high-quality aquarium gravel.

tropical fish 2 divider Conclusion

The bottom line is that while the gravel may seem like a minute point to keep in mind, it is actually quite important. So, be sure to take all of the factors into account and make the proper calculations before adding the gravel into your tank.

Featured Image Credit: Pixabay

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