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Rock Tumbler Loading: How Much Grit & Rocks Do You Put In?

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Loading your rock tumbler with rocks and grit can be a challenging task. Let’s face it, we all want to put in as many specimens in there as possible, and perhaps some of you might want to save on the grit, but the truth is, you can save it differently.

If you know how much grit & rocks do you put in your rock tumbler to maximize your tumbler’s full potential, you will save a lot of time and grit. Always clean your rock tumbler barrel before you begin a new tumbling process. With that being said, let’s see precisely how much grit and rocks are needed for rock tumbling!

If you are interested in checking out the best tumbling grits you can find them by clicking here (Amazon links).

How Many Rocks Do You Put in A Rock Tumbler?

How Many Rocks Do You Put in A Rock Tumbler? (source)

The first step of the tumbling process is the loading of the barrel. First, you will need to add the rocks.

The rough should fill 3/4 of the barrel’s size, or at least 2/3. During the process, the rocks will lose about 15-20% of their size, so you need to make sure that the recipient is filled incorrectly. You can use different rock sizes but make sure they are no larger than 1/2 of the barrel’s diameter. How many you put in depends on your tumbler.

If you don’t have enough rocks, you can use plastic pellets or ceramic media to take up the extra space. The tumbler will be at the proper operating level. A more significant change might be too much for the device’s rotor.

Pay attention to the plastic pellets. Some of them float, so you will need to make sure you add enough pellets to appropriately fill the required volume of the barrel before adding water. Also, keep in mind that you must use new pellets for the polishing phases.

How Much Grit Do You Put in A Rock Tumbler?

How Much Grit Do You Put in A Rock Tumbler? (source)

Next, you should add the grit. Like the rocks, how much grit you put in your rock tumbler varies. Depending on the barrel size, the amount of grit will always differ. 

All rock tumblers come with a chart that indicates the amount of grit you should be using at every phase of the process. However, if you lose the chart or you don’t have it at hand, a rule of thumb says to use 2 to 2,5 tablespoons of grit per pound of a load. Usually, you will start with about 80 grams of coarse silicon carbide grit. 

Depending on the rock’s hardness, you may start with the 120/200 grit instead of the 60/90 one. As we were saying, if the rocks have a hardness of 6 or below on the Mohs scale, coarse grit might break or scratch them.

After you sprinkled the grit, you start to add water. If you wonder how much water you should add, the answer is simple – the water level must touch the bottom of the top layer of stones. 

Before starting the tumbler, inspect the device and make sure the barrel is charged within the weight allowance for the motor to be used. 

Also, the sealing surface and the lid are clean. And don’t forget to monitor the tumbler for a few minutes to ensure there are no leaks. 

To conclude, load your tumbler barrel 2/3 to 3/4 full with the rough materials you have chosen. The grit quantity is listed on the tumbler’s chart shipped with the device. In case of need, the rule is to add about 2 – 2.5 tablespoons per pound of a load.

TIP: It is always good to know what rocks can be tumbled together and how long it takes to tumble different types of rocks. Check out these two articles below and find out how to get better results when you tumble rocks:


What‌ ‌Rocks‌ ‌Can‌ ‌Be‌ ‌Tumbled‌ ‌Together:‌ ‌Complete‌ ‌List‌ ‌With‌ ‌Tips‌


How Long Does It Take To Tumble Rocks? Values For Various Rocks


Materials Used in the Tumbling Process

Rocks and grit are not the only materials you use during rock tumbling. Find a complete list of materials used in the tumbling below.

  • Rock Tumbler

Currently, there are two available types of rock tumblers on the market: rotary and vibratory tumblers. Rotary rock tumblers are far more common than the vibratory ones, and they are amateurs’ favorites. So, a rotary tumbler will do just fine.

If you want to start with rock tumbling I recommend trying this simple rock tumbler first (Amazon link). It is cheap and the package contains everything you need to start tumbling.

  • Rocks

The rocks you want to tumble should have approximately the same Mohs hardness in a load. Otherwise, the results will be disappointing. Also, make sure the rocks you want to tumble do not have cracks, protrusions, or voids that may trap the grit.

  • Plastic pellets

The plastic pellets are used to fill up the tumbler’s barrel when you don’t have enough rocks. Another role is to protect the rocks if they are fragile. I recommend using these plastic pellets (Amazon link).

  • Grits

The rock-tumbling grit is a silicon carbide abrasive used to smooth, shape, and polish rocks. This hard material is the common choice for tumbling rocks due to its low price and characteristics.

  • Polishing compounds

The best choice for polishing the rocks is aluminum oxide, a cheap polish that works great on many types of rocks. It gives an excellent luster to agates, jasper, and many more.

  • Water

Make sure you add the right amount of water to the barrel. Too much liquid will affect the tumbling process as tumblers are very sensitive and require the right balance to work properly.

TIP: Do you know what to do then your rock tumbler starts to leak? It happens to everyone from time to time. Read more about the most common reasons why your tumbler leaks and how to fix it in the article below:


6 Reasons Why Your Rock Tumbler Leaks and How to Fix it


Rock Tumbler Loading

Before starting to load your tumbler barrel, make sure it is clean. This is an essential step in the tumbling process as it assures optimum results. 

Any grit or fragments of rocks left from the previous tumble will ruin the aspect of the stones. Also, during the tumbling process, you will use different types of grit. Coarse grit used during the medium grit phase can scratch the rocks, and you will have to repeat this phase.  

Another type of contamination is caused by the brittle rocks that might mix into the rough. Make sure you inspect the rocks before tossing them into the tumbler barrel.

Types of grit

Grit is the material that is used to shape your rocks. It is made from silicon carbide, a material with a 9 – 9.5 hardness on the Mohs scale. 

Different tumbling machines use different types of grit, different types of graded silicon carbide, to be more specific. Always check what type of grit your tumbler uses.

  • Coarse rock tumbler grit

During the first phase of the tumbling process, the coarse 60/90 silicon carbide is also called coarse grit. Its purpose is to grind rough rocks, and it is usually used during the first phase of the tumbling process.

  • Medium (120/200) fine grit

Made from the same material, silicon carbide, this type of grit is used for smoothing the surface of rocks after the initial shaping.

  • Pre-polish aluminum oxide grit

This type of grit is much finer than the previous ones, and it is used for the final polish of rocks.

  • Polish aluminum oxide grit

This grit has a similar granularity to the flour and, it is used to do the final polishing of the rocks.

If you are interested in checking out the best grit for rock tumbling, try to use this grit kit (Amazon link).

FAQ about Rock Tumbling Grits

Still did not find the answer to your answers about rock tumbling grits? Find frequently asked questions in the section below:

Can I reuse grit from a tumbler?

No, you cannot reuse grit. During the tumbling process, the grit breaks down and should not be used anymore, especially for the polishing stages. It will scratch your tumbled rocks. The rocks and the barrel must be thoroughly cleaned before passing to the next phase of the tumbling process. Polish can be reused several times though.

Find out more about reusing grit in this article.

Can I make my own grit?

Rock tumbler grit cannot be made at home if you do not have access to the compounds required to obtain silicon carbide. The common myth that sand or river silt might replace silicon carbide is just a myth. These common materials round up quickly during the tumbling process and become inefficient.

Can you tumble rocks without grit?

The whole tumbling process might take longer without grit, and the results are not as satisfactory as when you use proper grit. Sand or silica sand are among the alternatives used by most rockhounds. Sinterblast, an economic sintered aluminum oxide blasting grit, is also gaining popularity due to its low price and the fact that it is recyclable.

Do rock tumblers use a lot of electricity?

Rock tumbling is an expensive hobby. Depending on the area you live in and the tumbler’s motor’s size, the electricity bill can be high. Common models of rock tumblers consume exactly one kilowatt-hour of electricity per day and run continuously for 24 hours. If you don’t have a permissive budget, a better option would be to buy polished rocks.

TIP: Have you ever thought about using sand as grit? It sounds like a great and cheap idea but it is not so easy. Find out more about using sand during the rocks tumbling process in the article below:


Can You Tumble Rocks with Sand? Everything You Need to Know


Final Thoughts

Knowing the exact amount of rocks and grit that you should add to your rock tumbler barrel is not an exact science. The results depend on different factors like rock size, hardness, or quality. The amount of grit is also important. 

Although there are charts and articles on that matter, nothing compares to your experience. Getting the right amount of grit depends on what you observed in previous tumbles. Keep records of what works and what doesn’t. 

Polished stones can be easily purchased, but they will not look as beautiful as the ones you tumbled and polished yourself.

TIP: You need to find good rocks for tumbling before you start. Check out my guides with the best rockhounding locations in different states across the United States.


Where to Find Rocks & Minerals in the Different States in the US