How Much Gravel Do I Need for a Fish Tank? – A Detailed Guide

how much gravel do i need for a fish tank

It’s always challenging to do a tank setup for beginners, as there is a myriad of things to check and prepare. Among the most important steps for a good fish tank setup are picking substrate and calculating the right amount for your aquarium.

How much gravel do I need for a fish tank? In general, it is recommended to add one to 2 pounds of gravel per gallon. This rule indicates 10 gallons require 5 – 10 pounds of gravel, depending on the type.

Keep reading to know the exact amount.

How Many Pounds of Aquarium Gravel Do I Need?


Most aquarists use the thumb rule which is 1 – 2 pounds of substrate for every gallon of water to calculate the amount of gravel for aquarium.

Generally speaking, this rule means a 5 gallon tank will require about 3 – 5 pounds of gravel. Following that, you will need to purchase 15 – 20 pounds of gravel for 20 gallon tank.

However, this rule works well in theory and in a little tank! To choose the right substrate and work out the exact amount of gravel for a fish tank, there are many things that you need to take into consideration such as:

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  • The kind of fish you want to keep
  • The tank’s size and dimension
  • The plants you want to grow inside
  • Decorations


Since gravel is a very important component, it’s also crucial to choose the right type for your fish tank as each fish and plant requires different types of gravel.

Low-light plants, for example, often prefer crushed granite rock that helps top layers absorb water better and limit algae growth.

Besides, aquarium gravel comes with different advantages such as a substrate for plants, water evaporation reduction, and aesthetic appeal.

Calculate Gravel for Fish Tank


How much gravel do I need for an aquarium? To find out how many pounds or kg of gravel for a fish tank, you need to know exactly the tank’s dimensions and size.

It is said that each freshwater fish tank will require at least 2 inches of gravel. To estimate how much gravel for a 2-inch gravel depth in different tank sizes, here is the formula!

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  • [The tank length (inch) x The tank width(inch)]: 10 = The amount of gravel in pounds


Here is the detailed fish tank gravel calculation example!

Let’s say you have a 10 gallon tank, so the standard rectangle tank’s dimensions will be:

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  • The length: 20 (inches)
  • The width: 10 (inches)
  • The height: 12 (inches)


Following the formula, we got: (20 x 12): 10 = 20 (pounds)

The final answer of how much gravel is in a 10-gallon tank is 20 pounds.

To convert pounds to kg (kilograms), you need to divide the answer by 2.2.

For example: 20: 2.2 = 9.09 kg

How to calculate the amount of gravel in liters? To work out the quantity of gravel in liters, you need to measure the length and width of your fish tank in cm instead of inches and then carry on this formula!

So if you are looking for a formula to calculate the amount of gravel for a 40 litre fish tank, here is what you need:

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  • [Length (cm) x Width (cm) x 2] + 5% = Volume in liters


By using this formula, you can work out the amount of gravel for 100 litre fish tank, 60 litre, or any litre fish tank.

If you don’t want to use this formula, then try to convert litre to gallons.

Once you have analyzed all the above considerations and combined them with the formula, working out the amount of gravel for 30 litre fish tank or any tank size becomes much easier.

If you still find this aquarium gravel formula is so complex, you should use a gravel calculator.

Benefits of Gravel in the Aquarium

1. Aesthetic appeal

The aesthetic is one of the main reasons why fishkeepers add gravel to an aquarium. Gravel comes in a wide range of colors that can be used to create decorative patterns at the tank’s bottom.

2. Provide a home to beneficial bacteria


One of the most important functions of gravel is that it offers a home for beneficial bacteria to grow and spread. These bacteria play a crucial role in neutralizing fish food leftovers, fish waste, and decaying plant debris, which prevents the thriving of ammonia.

3. Filtration

A layer of gravel is greatly useful when it comes to collecting decomposed debris.

Small particles of decomposed debris or precipitates are supposed to get stuck in the gravel and give a visually cleaner tank. On the other hand, all the debris will float around the water if your tank had no substrate at all.

4. Beneficial to grow plants


Gravel is critical to keep aquatic plants for two main reasons:

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  • Firstly, a layer of gravel is a strong base to which aquatic plant roots attach.
  • Secondly, gravel is where these plants take nutrients for their growth.


Not only be a solid base for proper rooting activities, but this substrate layer also contains nutrients absorbed from fish waste and decaying organic matter, which is useful for the growth of plants

Important note:

Although gravel is good, never overused!

Too much gravel will lead to strong algae growth as it reduces the amount of water circulating through your tank. In contrast, the lack of gravel makes your plants not spread their roots out properly which leads to unnormal growth and even death.

What is more important? You should clean aquarium gravel frequently every month to prevent bacteria from growing.


Did you change the aquarium gravel?

In general, you don’t need to change the aquarium gravel frequently if you clean your fish tank gravel with a vacuum regularly and carefully. And it may be in your aquarium for several years with no problem.

It is recommended to clean the aquarium gravel at least once a month with a vacuum.

But if you notice the gravel substrate is getting dirty with detritus worms living inside, it’s time to change the gravel layer, or at least, you have to drain all of the water as well as remove and rinse the gravel thoroughly with clean water.

Why is the substrate used in aquariums?

When keeping fish, it is necessary to add a layer of substrate not only because of making an aquarium more attractive but also for other important purposes.

The substrate can be a home for good bacteria that helps keep the aquarium water safe and maintain a healthy fish.

The most common substrate is gravel, but it’s not just about buying the type of gravel you like and adding it to the tank. In fact, the type of fish you have in the aquarium is the main factor to determine which type of gravel you should purchase.

It’s always important to research everything first to choose the right gravel for your fish and plants as each type of them requires a specific substrate. Some fish species, for instance, flourish with finer gravel, while others may prefer digging into coarse gravel.

Things to Consider When Using Gravel in an Aquarium

1. Type of Fish

To determine the quality and quantity of substrate, you need to know what kind of finish you intend to add to your fish tank. This is because different fish species have their own gravel preference. Some of them love messing around with coarse gravel while others prefer digging in finer gravel.

2. Tank size

There is no doubt that the bigger the tank is, the more gravel you will need to build the base layer. So, knowing exactly the size of the aquarium helps you work out an accurate amount of gravel needed.

3. Plants

Not only fish, but the type of plants in your aquarium also affect the gravel. Plants without a root system get nutrients from the water so they tend to care less about gravel, whereas rooted plants will require a layer of finer gravel to thrive.


How much gravel do I need for a fish tank? Following the thumb rule, you should add 1 pound of gravel per gallon of water.

Adding gravel to a fish tank is important for filtration and maintenance. But it is necessary to keep the gravel layer and the aquarium as lean as possible by using vacuuming to avoid draining water and replacing gravel frequently.

Last but not least, no one can deny the important of gravel in a fish tank, you should do research and take all these above considerations before adding gravel into the aquarium.