# Rock tumbling grit chart: grit size, amount and time for each stage

Source: https://tumblegrit.com/blog/rock-tumbling-grit-chart
Published: 2026-10-01
Publisher: Tumble Grit

**Short answer:** Rock tumbling uses four grits in order: coarse 60/90 silicon carbide (step 1), medium 150/220 (step 2), fine 500 or 600 pre-polish (step 3) and an aluminum oxide polish (step 4). In a rotary tumbler each step runs about 7 days and takes about 2 level tablespoons of grit per pound of rock. Only step 1 changes the shape, so it is often repeated.

The chart is written for a rotary tumbler and for hard rock around Mohs 7: agate, jasper, quartz and petrified wood. That covers most rough sold for tumbling. Brands name the steps differently and a few grit numbers differ too, so each row lists the common alternatives. Kit tumblers that ship with one packet per step follow the same order, with times printed in their own manual. Soft stones and vibratory bowls change the schedule, and both are covered below the chart.

## Rock tumbler grit chart: the four steps

Read the chart from top to bottom and do not skip a row. Each grit is finer than the one before it and only has to erase the scratches the previous grit left. Times are typical for a rotary barrel that is about 2/3 full and runs around the clock. The burnish row is optional.

| Step | Grit | What it does | Typical time | Done when |
| --- | --- | --- | --- | --- |
| 1 Coarse | 60/90 silicon carbide | Grinds off edges and pits. The only step that changes the shape | 7 days per run. Jagged rough often needs 2 to 4 runs | Every stone is rounded, with no pits, cracks or flat broken faces |
| 2 Medium | 150/220 silicon carbide (120/220 in some brands) | Removes the coarse scratches and smooths the surface | About 7 days | Smooth and evenly matte, no coarse scratches |
| 3 Fine (pre-polish) | 500 or 600 silicon carbide (1000 aluminum oxide in some kits) | Removes the medium scratches and readies the surface for polish | About 7 days | Dry stones look satin and feel silky |
| 4 Polish | Aluminum oxide polish (cerium oxide and tin oxide are also used) | Brings up the shine. Removes almost no rock | 7 to 10 days | Dry stones shine |
| 5 Burnish (optional) | No grit: grated plain bar soap or borax | Washes off polish film and brightens the shine | 1 hour to 1 day | Rinse water runs clear |

Rotary tumbler, hard rock around Mohs 7 (agate, jasper, quartz). Times are typical ranges from tumbler manuals and hobby references.

Note: Rinse the stones, barrel, lid and lid seal between every step. One grain of coarse grit carried into the polish barrel scratches the whole batch.

## How much grit to use in each stage

The amount is the same in steps 1 to 3 and for polish: about **2 level tablespoons per pound of rock**. A barrel's rating counts rock, water and grit together, so a 3 lb barrel holds about 2 lb of rock and takes about 4 tablespoons. Count ceramic media and plastic pellets as rock when you measure. Add water to just below the top layer of rocks. For other barrel sizes, the [grit calculator](https://tumblegrit.com/tools/rock-tumbler-grit-calculator) turns the weight of the load into tablespoons.

Fill level matters as much as the grit. Keep the barrel between 1/2 and 3/4 full at every step, with about 2/3 as the target. Below half the stones slam and chip, and above 3/4 they cannot tumble. Rocks lose volume in step 1, so top the load up with ceramic media before the later steps. Mix sizes from small to large so the load rolls instead of sliding.

## Rotary vs vibratory tumbler: how the chart changes

A vibratory tumbler does not shape rough, so there is no coarse step in the bowl. Jagged rock is rounded in a rotary barrel first. Steps 2 to 4 can then move to the bowl, where each takes about **2 to 3 days** with a daily check. The grit grades stay the same. What changes is how much goes in and how wet the load is.

| Setting | Rotary tumbler | Vibratory tumbler |
| --- | --- | --- |
| Coarse step | Yes. Shapes the rough | No. Shape in a rotary barrel first |
| Grit per pound of rock | About 2 level tablespoons | On the order of 1/2 tablespoon or less |
| Water | To just below the top layer of rocks | Only enough to wet the load into a thin slurry |
| Time per step | About 7 days, polish 7 to 10 days | About 2 to 3 days for steps 2 to 4 |
| How often to check | At the end of each run | Daily |

Typical figures. Vibratory amounts differ a lot by maker, so the bowl maker's chart is the final word.

[Rotary vs vibratory: which to choose](https://tumblegrit.com/blog/rotary-vs-vibratory-rock-tumbler)

## What is rock tumbler grit made of?

Steps 1 to 3 use silicon carbide, a man-made abrasive of about Mohs 9 to 9.5. That is why it cuts quartz-family rock at Mohs 7, and why sand, which is mostly quartz, does not. The grains are sharp and brittle. They break down as they work, so after a week the coarse grit is spent mud and cannot be reused. Polish is a different material: a very fine oxide powder, most often aluminum oxide, that smooths the surface instead of cutting it.

| Step | Abrasive | Grade on the label | Looks like |
| --- | --- | --- | --- |
| 1 Coarse | Silicon carbide | 60/90 | Black or dark gray grains you can see and feel |
| 2 Medium | Silicon carbide | 150/220 or 120/220 | Dark gray, like very fine sand |
| 3 Fine (pre-polish) | Silicon carbide, or aluminum oxide in some kits | 500 or 600, or 1000 | Fine powder with no grains you can feel |
| 4 Polish | Aluminum oxide, cerium oxide or tin oxide | Sold by name, not by grit number | Very fine powder, often white |

What is in the bag or packet at each step. Useful when packets have lost their labels.

## What do rock tumbler grit sizes mean?

The number is a mesh size, tied to the number of openings per inch in the screen used to grade the grains. A higher number means a finer grit. A double number such as 60/90 is a graded mix, with grains that run from 60 mesh down to 90 mesh. Larger grains do the heavy cutting and smaller ones reach into hollows.

Read the step, not only the number. 120/220 and 150/220 are both medium grit. 500, 600 and 1000 are all sold as fine or pre-polish. A [four-step grit kit](https://tumblegrit.com/best/best-rock-tumbler-grit-kit) labels each bag by step, which removes the guesswork for a first batch.

## When the chart changes: soft stones and kit tumblers

The chart assumes one hardness in the barrel. Never mix hard and soft stones in one load, because the hard ones grind the soft ones away. Fluorite (Mohs 4), malachite (3.5 to 4) and calcite (3) need their own load and a gentler schedule, and many hobbyists skip coarse grit for them. Obsidian and glass, at about 5 to 5.5, chip easily and want a fuller barrel, cushioning media and more frequent checks. The [hardness chart](https://tumblegrit.com/blog/rock-tumbling-hardness-chart) lists common rocks by Mohs number.

Kit tumblers with grit packets, National Geographic and similar, are set up for one packet per step and often quote shorter times. Follow the kit manual for packets, and expect better shape from a longer step 1. The page on [National Geographic tumbler grit amounts and times](https://tumblegrit.com/blog/national-geographic-rock-tumbler-instructions) covers those kits.

## How to use the grit chart at the tumbler

Print the first table or save a screenshot and keep it next to the machine. The chart gives the order and the target for each step. The days are a starting point, and [how long to tumble rocks](https://tumblegrit.com/blog/how-long-to-tumble-rocks) explains what stretches each step.

- Go by the Done when column, not the calendar. A load that fails the check at day 7 gets another run with fresh grit.
- Dry a few stones before judging them. Wet stones look polished at every step and hide scratches and pits.
- Stones that fail stay in the same step or wait in a labeled bag for the next batch. Do not carry them forward.
- Write the start date, step and grit amount on a log sheet so you do not lose count of repeat coarse runs.

## Quick answers

Short answers to the most common grit questions, taken from the chart above. All figures are for a rotary tumbler and hard rock.

- **What is rock tumbler grit?** Silicon carbide abrasive sold in graded sizes. It is harder than quartz, so it grinds and smooths rock as the barrel turns.
- **What are the rock tumbling stages?** Coarse, medium, fine (pre-polish) and polish, in that order. A short soap run, called a burnish, is an optional fifth step. See [burnishing tumbled rocks](https://tumblegrit.com/blog/burnishing-tumbled-rocks).
- **What grit sizes does a rock tumbler use?** 60/90 for coarse, 150/220 for medium, 500 or 600 for fine, then a polish powder such as aluminum oxide.
- **How much grit goes in each stage?** About 2 level tablespoons per pound of rock, the same amount in all four steps of a rotary tumbler.

## Gear guides for this topic

- https://tumblegrit.com/best/best-rock-tumbler-grit-kit
- https://tumblegrit.com/best/best-coarse-rock-tumbler-grit
- https://tumblegrit.com/best/best-pre-polish-rock-tumbler-grit
- https://tumblegrit.com/best/best-rock-tumbling-polish

## Sources

- [RockTumbler.com: Rock Tumbler Instructions](https://rocktumbler.com/tips/rock-tumbler-instructions/)
- [Lortone: Rotary Tumbler Instructions and Parts List, Model 3A](https://lortone.com/cdn/shop/t/4/assets/3A_Tumbler_Instructions.pdf?v=13653966622304219831524508937)
- [Geology.com: Mohs Hardness Scale](https://geology.com/minerals/mohs-hardness-scale.shtml)