How to Calculate the Volume of an Aquarium

It may sound like an easy question, but it can be complicated. To calculate the volume of an aquarium, you have to look at the shape of the fish tank. 

There are different formulas for rectangular, rounded, and cylindrical tanks. Your units will also change the equation for gallons. 

Here are some common equations you can use to find the volume of the aquarium.  

Calculating Volume for Rectangular or Square Aquariums

Rectangular or square aquariums are the most common type of tank. They are usually the largest tanks, and you see them everywhere. 

They are also some of the most straightforward tanks to calculate volume. All you have to do is multiply the height, width, and length of the tank. 

This calculation will give you cubed versions of whatever unit you used. So if you measure it in inches, it will be cubed inches. 

The equation is

H x W x L = volume. 

You can use any unit, but keep them all the same for each measurement. 

A square is a little easier.

The height, width, and length are all the same in a cube. You only need to measure one and then cube it. The equation for a cube is

L^3 = volume. 

If you’re not sure you have a cube, measure all three dimensions. If they are all the same, it’s a cube. If not, it’s a rectangle. 

If your aquarium is a strange shape, you can sometimes break it into multiple rectangles. All you have to do is take the measurements of each.

Multiple the individual pieces and add them up.  

Once you have the total volume of the aquariums, you can find the gallons. It takes one more step. 

Calculating Volume for Rounded Aquariums

Figuring out the volume of a rounded or bow-front aquarium can be a little more complicated. 

First, you’re going to calculate the rectangle area portion. Then you have to find the elliptical area. 

For the rectangle, you multiply width, and length. For the width, you only measure the distance to where the elliptical part starts. 

With the elliptical, you take the width from the furthest portion of the oval. Then subtract the rectangle width. Multiply the calculated width, length and divide them in half. Then multiple by Pi 3.16. 

Now add the two areas together and multiple by the height. You will get the entire tank volume. You will get the value in the cubic form of the measurement you used.  

The whole equation is:

(w x l) + π(((w-full w) x l)/2)x h = full volume. 

You can use any unit. Just make sure they are the same for each measurement. 

Calculating Volume for Cylindrical Aquariums 

If you have a cylindrical tank, there is a unique formula you need. Circles have their own math for aquariums. 

Make sure your tank is actually a cylinder though, if it is not, you may need another formula. To check, the measurement of the diameter should be the same. 

There shouldn’t be a change anywhere on the circle. If there is a difference, it may be an ellipse or an oval. 

To get the volume, you have to measure the diameter of the circle. Then divide it in half to get the radius. Square the radius, and multiply it with the height and Pi.  

The final equation is

r^2 x h x π. 

If you don’t have a calculator, Pi can equal 3.16 or 22/7. Both of these values will give you very close results.

Half Cylindrical Aquariums

If you have a half-cylindrical tank, you can use the same equation for cylindrical. Then divide it in half for your tank. When you measure the diameter for a half-cylinder, use the back length.  

That equation would be

(r^2 x h x π)/2

You can use 3.16 for Pi again. 

If you’re not sure the tank is a half-cylinder, find the radius. Then measure the radius on the back of the tank. Measure from the end of that radius to the edge. 

That length should be equal to the radius. If it’s not, you don’t have a half-cylinder. It is likely elliptical. 

Calculating Volume for Elliptical Aquarium 

An elliptical Aquarium can sometimes be a little more challenging to figure out. You have to find the radius of the long side and short side. 

Once you have those, measure the height, and multiply everything by Pi. The final equation is

rMajor x rMinor x h x π = Volume. 

Finding these measurements is often more challenging. It may be hard to get the precise value this way. 

Try to take both lengths at the exact center of the ellipse. This method gets the best results.

Other Shapes of Aquariums

You have the most common tank shapes covered above. However, there are some custom tanks and irregular-shaped tanks. If you don’t think these are your tank’s shapes, don’t worry. 

Often you will have to calculate two different shapes and add them together. Sometimes this can make getting measurements harder.

It helps to draw the tank on paper to keep track.  

If you can’t break it, there are other methods. Some unique shapes have formulas that mathematicians figured out. 

Check out how to get the shape’s volume on a math site. Once you have the volume, you can still figure out the gallons.

Make sure you convert the volume with the correct measurements. 

Figuring Out the Gallons 

Once you have the volume, it is easy to convert it to gallons. The measurement units you used will affect this step. That’s because the number of gallons that fit in different units varies. 

You can switch between volume and gallons if you know one and need the other. It is a simple conversion. 

If you use inches, you can divide by 231.

There are 231 cubic inches for every gallon. So the final equation for gallons in your tank is V/231= gallons. 

Being able to get the gallons of a tank can be crucial. It can make figuring out many additives easier.  

All the Different Measurements 

There are many other measurements you can use when figuring out your tank size. For huge tanks, feet may be better. In some countries, you may want centimeters or meters. 

If you use a measurement other than inches, you can still get the gallons. If you used cm, you could divide by 3,785. There is 3,785 cubic cm per gallon. So the equation is V/3,785= gallons.

When you use feet, there are more gallons per cubic foot of tank. So you have to multiply by 7.5 gallons. The equation is V x 7.5= gallons. 

If you prefer to use liters, you can easily convert the units. Gallons equal 3.9 liters. So once you have gallons or liters, you can change quickly. 

If you have gallons, you can multiply by 3.9 to get liters. If you have liters, divide by 3.9 to get gallons. It is easy to change your measurements into whatever unit you need. 

What If You Don’t Fill the Tank? 

In many cases, you might not fill the tank. Putting in less water will change the volume of the tank. You can come close to how much water you put in the tank. 

When you need to know how much water you added, change the height measurement. It should only be up to the top of the water, not the tank.  

Once you have the correct height, plug that number into the equation. You will get the right size of the water you use in the tank. 

If you almost fill the tank to the top, you probably don’t have to worry. When you use the tank for turtles or frogs, there could be a big difference. That’s when this step comes in handy. 

Remember that this number will change as you add or lose water. Using this method will mean you have to calculate every time. 

Why Do I Have to Know the Tank Volume? 

There are a lot of reasons you may have to know the volume of the tank. Some fish and plants need specific amounts of space to thrive. 

Often this number is calculated in the volume or gallons of the tank. 

It can help figure out how much salt to add to a saltwater aquarium. The exact amount can be vital for your fish.  

Some animals become more aggressive in smaller areas. If you know the size of the tank, you know what fish can live together. 

At times you may have to add chemicals to the tank. These can help maintain the balance of the water.

You may also have to add something to treat problems with the fish. 

Almost everything you need to add to a tank needs to know the volume. Once you figure it out, you might want to write it down. That will make it easier to find next time. 

Now That You Have the Measurements

The volume of your tank can be essential. It is necessary when you have to maintain the chemistry of the tank. If your measurements aren’t correct, it can be a problem.  

You may need to know the cubic volume or the number of gallons the tank holds. With these equations, you can get both answers. 

Now you can add the proper measurements to help take care of your tank. It will ensure the safety of your fish and plants in the aquarium.

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